applications of redispersible powders

329

13

Applications of Redispersible Powders

Hermann Lutz and Christoph Hahner

13.1

Introduction

The building/construction industry is the main industry for redispersible powders.Over the years the usage of dry mortar technology has been developed dramaticallyand modernized the way mortars are being used on a job-site. The invention of re-dispersible powders enabled the industry for the first time to produce pre-packed,polymer modified building materials that needed only the addition of water beforeapplication. These materials, known as dry mortar mixes guarantee defined and con-sistent performance of construction materials.

In the past up until to the 1950s mortars were exclusively used and applied as job-site mixed mortars, where the mineral binder (mostly cement) and the aggregates(mostly silica sand) were transported separately to the job-site. The aggregates andthe mineral binders were then mixed together by hand in the appropriate ratio andwere gauged with water in order to obtain the fresh mortar ready to apply.

During the 1950s and 1960s both in Western Europe and the US, but especially inGermany, there was a fast growing demand in the construction industry for newbuilding materials and technologies. Several reasons, like shortage of skilled work-men, the need of shorter construction time together with cost reduction, increasinglabor costs, the diversification of building materials suitable for specific applications,the request for new materials and an increased demand for better quality of con-structions were supporting a movement towards dry mix mortar technology.

The job-site mix mortar technology is not able to meet adequately all these re-quirements. As a practical consequence, the development of the modern construc-tion and building chemical industry in the countries of the West from the 1960s on-wards was influenced mainly by two important trends, which can be seen nowadaysin the whole world. First there was a replacement of the job-site mixed mortars bypremixed and pre-packed dry mix mortars, which are more and more applied withmachines. Secondly mortars started to be modified with polymer binders in order toimprove the product quality and to meet the requirements of the modern buildingindustry. As a consequence the two-pack systems (mortar + dispersion) as well as

Polymer Dispersions and Their Industrial Applications. Edited by Dieter Urban and Koichi TakamuraCopyright © 2002 Wiley-VCH Verlag GmbH & Co. KGaA

ISBNs: 3-527-30286-7 (Hardback); 3-527-60058-2 (Electronic)

330 13 Applications of Redispersible Powders

ready to use products (liquid or paste) were substituted by one-pack systems, whichare modified with redispersible powders, pre-mixed and pre-packed dry mix mortars.

13.2

Manufacturing of Redispersible Powders

A redispersible powder is by definition a polymer in a powdered form that can beredispersed by adding water to it. The resulting emulsion will fulfill the functionali-ty of a polymeric dispersion binder, normally within a cementitious or gypsum basedsystem. Redispersible powders are manufactured by spray drying an emulsion (Fig. 13-1).

Over 90 % of all industrial manufactured polymer dispersions are produced byemulsion polymerization. The most important monomers, which are being used forapplications in the building/construction industry, are vinyl acetate, ethylene, versa-tic acid esters, vinyl chloride, styrene and acrylics. Especially the use of ethylene as aco-monomer offers some extraordinary advantages:– environmentally safe,– no saponification,– UV-resistant (no yellowing),– very hydrophobic,– ideal for co-polymerization with vinyl acetate,– very low glass transition temperature, Tg, of –93 °C,– very flexible, and– good adhesion to most of the substrates.

To guarantee the performance of a redispersible powder in its final application aprotective colloid is added to the emulsion before the spraying process. The colloidprotects the polymer particles from film forming during the spray drying process

Fig. 13-1 Spray-driedpolymer particle.

13.2 Manufacturing of Redispersible Powders 331

and is also responsible for that the powder will redisperse in water again (Figs 13-2and 13-3).

Fig. 13-2 Dispersion/redispersion – comparison of particle size distribution.

Fig. 13-3 The spray-dry process.

dispersion protective�colloid

redispersible�powder

redispersion

spray�drying

adding�water

drying

dispersion

redispersion

particle concentration particle concentration

particle concentration particle concentration

particle size (diameter)

particle size (diameter)

0 2 4 6

69ppm

69ppm

92ppm

92ppm

0 2 4 6

wei

ght

dis

trib

utio

n cu

rve

wei

ght

dis

trib

utio

n cu

rve

1 1 10

1 1 10

100%

80

60

40

20

0

100%

80

60

40

20

0


Over the years poly vinyl alcohol (abbreviated PVOH or PVAl) proofed to be themost preferred protective colloid for that purpose. In a cementitious environmentPVOH will be partly saponified and also absorbed of fine particles within a mortar,i.e. cement and fillers. This results in a film forming of the dispersed polymer and fi-nally the polymer film is not redispersible any more. Since the polymer film (actingas a binder) is distributed throughout the cement matrix it improves dramatically theadhesion, abrasion resistance, flexural strength, flexibility, water impermeability/wa-ter repellency (hydrophobicity) and workability of a cementitious system.

13.3

Dry Mortar Technology

The invention of redispersible powders by Wacker-Chemie in 1953 made for the firsttime the production of polymer modified dry mix mortars possible, which are nowa-days referred to as one pack or one component system (“bagged” materials). Newconstruction methods and building materials, which had the need for more safety,reliability, durability, efficiency and economy, have been achieved by using modernmethods like the dry mix mortar technology. As a consequence worldwide the “job-site mix technology” and the modification of mortars with liquid polymers on job-sites were and are substituted by polymer modified dry mix mortars. The productcharacteristics are very well adapted to the requirements of modern constructiontechnologies, materials and climates.

Pre-mixed and pre-packed dry mix mortars not only increase significantly the pro-duction performance and the productivity on construction sites, but guarantee alsothat high and constant quality binder, aggregates, and additives are being mixed ex-actly in the same ratio, thus ensuring a consistent high quality level within dry mixmortars. Furthermore, dry mix mortars offer solutions to specific problems that areprecisely tailored to certain types of construction/material specifications. Especiallyin the USA, the legal aspect of a reliable, properly conducted construction job is veryimportant to each manufacturer of construction materials.

The use of redispersible powders and therefore also the use of polymer modifiedpowdered mortars is already for many decades standard in the construction industryin Europe and North America (predominantly in the USA). Other marketplaces allover the world like South America, Asia, Africa and Australia are in the process fol-lowing that example. More and more environmental reasons ask also for the usage ofdry mortars, since the recycling of buckets becomes more and more an issue. Drymortars are also easy to store, transport and do not require biocides.

Typically dry mortar mixes contain the components listed in Tab. 13-1 and aredefined according to German standard DIN 18557.

The application areas of dry mix mortars are:– ceramic tile adhesive,– tile grouts,– E.I.F.S. (exterior insulation and finish systems)/E.T.I.C.S. (exterior thermal insu-

lation compounds),

13.4 Markets and Application Areas of Redispersible Powders 333

– self-leveling over- and underlayments, screeds,– stucco, skim coat,– topcoat/finish coat,– patch and repair mortar,– adhesive mortars (for all kind of substrates),– crack isolation membrane,– powder paints,– gypsum based compounds (joint fillers),– waterproof membranes/sealant slurry,– pool decking, and– stamped concrete.

The following paragraphs will describe the most important and most developedapplication areas for redispersible powders as they are ceramic tile adhesives/ tilegrouts, thermal insulation systems (E.I.F.S.), self-leveling underlayments, patch andrepair mortars, as well as water proof membranes (sealant slurries).

13.4

Markets and Application Areas of Redispersible Powders

To meet today’s technical requirements, almost all dry mix mortars require polymermodification. Many cementitious mortars contain cellulose ethers as an additive toimprove water retention and workability. However, after setting and drying they willadhere poorly or not at all to most of the substrates used in modern constructiontechnology such as polystyrene panels, fiber panels, wood panels, closed and non-ab-sorbent substrates or old tiles. In addition, cementitious mortars are very hard, brit-tle and inflexible materials, whereas for many applications flexible and deformablecementitious materials are essential. As a consequence for almost all applications inmodern construction, the modification of cementitious mortars with polymers is amust. In dry mix mortars the mineral binder, cement, and the polymer binder, re-dispersible powder, are ideal partners. The combination of both in a dry mix mortar

Tab. 13-1 Dry mortar mixes.

Mineral binders Aggregates fillers Polymer binder Additives

Portland cement (OPC) Silica sand Redispersible powder Cellulose etherHigh Alumina Cement (HAC) Hydrated lime PigmentSpecial cement Dolomite sand DefoamerHydrated lime Marble sand Air-entraining agentGypsum, Lightweight fillers Retarderanhydrite Special and functional fillers Accelerator

ThickenerHydrophobing agentsPlasticizers


provides outstanding synergistic properties and characteristics, which cannot beachieved by either of the binders alone.

13.4.1

Adhesives for Ceramic Tiles

Ceramic tiles as well as natural stone were previously installed exclusively by usingthe thick bed mortar technique. Silica sand and cement were mixed together on thejob-site, in order to produce a simple cement mortar with a cement/sand ratio of ap-proximately 1:4 to 1:5. In some countries only cement is still used in order to settiles. After having applied (“buttered”) the mortar at a thickness of 15 to 30 mm (0.6to 1.2 inch) on the reverse side of the water-soaked or pre-wet tile, the tile is pressedinto the pre-wet surface. The tiles have to be tapped to ensure uniformity and flat-ness of the tile surface, thus obtaining a final mortar bed of 10 to 25 mm (0.4 to 0.8inch). This procedure causes not only compaction of the mortar, but leads in addi-tion to the migration of the fine cement particles into the porous back side of the tilesand the porous substrate as well. This process assures the mechanical fixing of thetile in the mortar bed. This type of mortar has no slip resistance. Therefore tiling ofa vertical substrate has to be started at the bottom and distance splinters becomenecessary. The described procedure shows very clearly that the thick bed method is avery time, cost and material consuming process. More significantly, there are tech-nical restrictions using this technique. One of the examples is that only small,porous tiles can be applied over porous, solid and strong mineral surfaces. The ap-plication of tiles over wood would be almost impossible, since a mortar without anypolymer modification would not only be not flexible enough to withstand the move-ment of a wood substrate over an extended period of time, it would also have no suf-ficient adhesion to the substrate. Consequently severe damage could occur andtherefore the thin bed mortar technique has replaced the thick bed mortar techniquein most industrial countries.

It started in the USA in the early 1950s by adding a polymeric binder in form of aliquid latex dispersion to a job-site mixed mortar (see Chapter 8). Nowadays dry mixmortars modified with redispersible powders dominate this market segment moreand more. After gauging the polymer modified dry mix mortar with water, it can beapplied with a notched trowel, producing a ribbed mortar bed of uniform thickness.Due to the good water retention capacity of the thin bed mortar, neither the tiles northe substrate have to be pre-wet. The tiles are pressed into the thin layered mortarwith a slightly twisting movement of the tile. An anti-sag ceramic tile adhesive allowsinstalling tiles on vertical substrates without using distance splinters between thetiles. The tile installer can also start from the top of the wall instead of the bottom.The mortar bed, which fixes the tiles, has a thickness of approximately 2 to 4 mm (upto 0.25 inch). Since this method clearly uses less material, it is more cost effective,can be used more universally; its execution is clearly simpler, faster and safer. Theclear advantages of dry mix mortars modified with redispersible powders, which ap-ply also for tile grouts, are:


– good workability, fast and easy to use, creamy consistency,– good water retention, which results in a long open time and good adjustability

even at high temperatures, and– substantial anti-sag properties, if required.

As far as the formulations for ceramic tile adhesives go there is a high variety ofmortars offered in the market place in order to meet all the specific requirements. Amajor difference, for example, between Europe and the United States is the usage ofwood as a substrate in the USA. Differences in the formulation are also determinedby requirements of specifications or application circumstances like interior or exteri-or, wall tile or floor tile, vitrified tile or more porous tile, fast setting or regularsetting, flexible or even highly flexible. The availability of certain raw materials i.e.silica sand determines very often how a formulation will perform.

The two most important specifications worldwide are the European Norms “EN”and the American Standards ANSI 118.1-1999. The biggest difference between thetwo standards is the principal test setup. The European Standards require mostlytensile bond adhesion testing where else the American Standard uses shear bondtesting. The other difference is clearly the storage conditions for the specimen beforetesting. A listing of both standards is shown in Tab. 13-2.

Cement-based standard tile adhesives can be classified in very simple (low quality)tile adhesives, which do not contain any polymeric binder. They do not meet Euro-pean or American Standards. Such tile adhesives, providing a pure mechanical fixa-tion can only be used for fixing small, very porous tiles. The substrate is supposed tobe dimensionally stable, sound and solid as well as not showing any shrinkage ormovement. If exposed to higher temperature or frost, there is a higher risk of failure.Non-modified mortars show for the most part no long-term performance.

Simple tile adhesives have already a polymer modification of 1 to 1.5 % of a redis-persible powder (calculated on total formulation). Such tile adhesives meet someparts of the mentioned national standards, but usually fulfill not all requirements.Only the usage of tiles with a medium porosity and small size could result in accept-able results with these types of adhesives.

Tab. 13-2 EN and ANSI standards for CTAs.

European standardsEN 12004 Definitions and specificationsEN 1308 Anti-sagEN 1347 Wetting capability (coverage)EN 1346 Open timeEN 1348 Tensile adhesion testing, including heat and freeze-thaw storageEN 1324 Shear-strength for masticsEN 12002 Deformability of cementitious CTA

US standardsANSI A 118.4 Specifications for Latex Portland cement mortarANSI A 118.11 Specifications for EGP (exterior glue plywood) Latex–Portland cement mortar


Standard ceramic tile adhesives of good quality need approximately 1.5 to 3 % ofredispersible powder on total dry mix. They meet the new European Norm for tile ad-hesives (mostly only C1 level) and pass also the ANSI specification 118.4 and 118.11.Larger formatted tiles can be applied with these materials over porous or less porous,dimensionally stable substrates. They are suitable for interior as well as exterior ap-plication. For standard applications these modified mortars provide higher qualitysecurity and a certain long-term stability, very much depending on the factors likeclimate conditions, weight traffic etc.

Finally flexible (5 to 8 % of redispersible powder) and very flexible ceramic tilemortars with a polymer modification beyond 8 % up to even 25 %, guarantee the bestperformance over all, very good adhesion on all types of substrates with all types andsizes of tiles. These adhesives are used more universally and offer a much greater ap-plication variety, safety, as well as long-term durability and reliability. Nowadaysthese mortars are more and more used to fix the very popular highly vitrified tiles(water absorption <0.1 %) and natural stone tiles (like marble) in any format. Thesubstrate can be non-porous and inorganic as well as wood. Even if the substrate stillshows to a certain degree of shrinkage or expansion, including other types of move-ments or vibrations, these quality adhesives could be used to set tiles in a safe anddurable way. Typical application examples for flexible ceramic tile mortars are:– floor heat system within the substrate,– to heat exposed surfaces, like i.e. tiles on a porch exposed to sunlight,– tiles over tiles,– over gypsum boards,– over backer boards,– over wood,– on water proof membranes,– on thermal and sound insulation panels, and– on light-weight concrete blocks.

Tests conducted by international research and test institutes have proved that it isof high importance that cementitious adhesives provide a sufficient deformabilityand a certain degree of plasticity [1–4]. Only in that way, long-term durability andfunctionality can be guaranteed. Adhesive mortars have to be able to absorb stressesthat occur between two materials as tiles and substrate in order to prevent damages.Typical damages are cracking or even delaminating of the tiles. Irreversible differen-tial movement, such as shrinkage causes always stress between tile and substrate(fresh concrete is always likely to shrink). Reversible movements of the substrate likevibrations and thermal movements due to heat or cold are also sources of stress be-tween substrate, adhesive and tile. The different modulus of elasticity of tiles andsubstrate is also enhancing the stress within a ceramic tile mortar (Fig. 13-4).

European Norm EN 1348 addresses this issue in a heat test as well as in a freeze/thaw test. Shear stress between substrate and tile normally concentrates in the pe-ripheral zones of a tile. That means, the bigger the tile the higher the flexibility of theadhesive has to be in order to avoid cracking or delaminating of the tile. The flexibil-ity (deformation capability) of a ceramic tile adhesive depends on the polymer/ce-ment ratio. It is one of the two most important ratios to be determined in a ceramic


tile mortar (the other one is the water/cement ratio). The German test DIN 18156/3,as well as EN 12002, measures the flexibility of ceramic tile adhesives. As a result ofthese tests it can clearly be shown, that the higher the polymer/cement ratio thehigher the flexibility of a mortar system (Fig. 13-5).

It is very important to mention that the deformation capability of a given cementi-tious system also depends to a large extent on the degree of hydration of the cement.Consequently, the flexibility of different adhesives can only be compared at identical

Fig. 13-4 The stress between substrate and tile.

initialdimension

initialdimension

initialdimension

initialdimension

shrinkage of substrateeg. shrinkage of concrete

expansion of tileseg. thermal expansion

tiles

deformableadhesive mortar

substrateeg. concrete

tiles

rigid, non-deformableadhesive mortar



tiles

tiles

substratreeg. concrete

Fig. 13-5 The flexibility of ceramic tile adhesives.


degrees of hydration of the cement. Unfortunately this is very often not consideredwithin the storage conditions of different standards, that deal with the testing of flex-ibility (Fig. 13-6).

The relative humidity of approximately 95 % at the beginning is not kept constantduring storage and is not sufficient for a full hydration of the cement. Over the timecementitious adhesives will reach their full hydration thus resulting in sometimesvery low flexibility of the mortar. For example, the use of additives and/or polymerswith a strong retardation effect on the cement will cause an incomplete hydration ofthe cement and will lead temporarily to a higher polymer-to-cement ratio. The flexi-bility measured at this point will not reflect the real flexibility of the system after fullhydration of the cement phase. After complete hydration of the cement, “soft” poly-mers (lower glass transition temperature, Tg) will perform at an appropriate dosagelevel better compared to polymers with a higher Tg, especially if used and tested atlower temperatures (Fig. 13-7). (The glass transition temperature describes the flexi-bility of a polymer. The “rule of thumb” is the lower the Tg the higher the flexibility.Tg is determined from the ratio of different monomers and their individual Tg in apolymer, by use of the Fox equation [5]).

The adhesion of tiles to the substrate is certainly as important for a ceramic tile ad-hesive as the flexibility. The European Norm uses a “pull off test” to determine theadhesion, where as the US standard ANSI 118.1 – 1999 prefers the shear bond test.A simple ceramic tile mortar with no polymer modification will fail in the adhesiontest especially after heat aging or over wood (ANSI 118.11 – 1999). The same mortarmodified with only 2 % of redispersible powder will pass both tests. With the pull-off

Fig. 13-6 EN 12002 results on flexibility.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

50% Portland Cement 40% Portland Cement 35% Portland Cement 30% Portland Cement

Traverse deformation test according to EN 12002 - 5% polymer modification at different cement levels

Fle

xio

n/d

efo

rmat

ion

[m

m]

standard conditions water storage (full hydration) 7d sc/ 14d in water/ 21d sc


test, it can be demonstrated that a ceramic tile adhesive without polymer or with alow polymer level will only be able to pass, if wall tiles (very porous, high absorptivetiles) are used. In addition, it can be demonstrated that only a sufficient amount ofredispersible powder provides a significant adhesion on critical substrates like PVC,wood or tiles (Fig. 13-8).

A sufficient high polymer modification of the ceramic tile adhesive is necessary es-pecially when non-porous, highly vitrified tiles (low to no water absorption) are used.In this case, there will be no mechanical anchoring like described earlier for poroustiles. The redispersible powder (chemical bonding), in this case, only provides the ad-hesion. This is, besides the outlined reasons for sufficient flexibility, another impor-tant factor for a higher polymer modification.

A ceramic tile adhesive that performs very well over almost all substrates, with alltypes of tiles (size, water absorption) should contain at least 6 % of redispersiblepowder and the cement content should be limited to 30 to 35 %. An adhesive formu-lation that considers these two important components at the right amount is verylikely to pass all international standards. However, in an adhesive formulation hasmore to be considered than only the polymer and cement level.

Fig. 13-7 Flexibility at lower temperatures.


13.4.2

Tile Grouts

Tile grouts, which are used to fill the joints in between the tiles, are very similar to ce-ramic tile adhesives in their formulations. They are expected to be water repellent(hydrophobic), to have good adhesion to the substrate and the edges of the tile, suffi-cient hardness, a low tendency for staining, cohesion strength, abrasion resistanceand flexibility. In the USA the field of tile grouts is much more diversified than, forexample, in Germany, because US manufacturers offer a much greater variety of col-ors. Therefore, color consistency is of high importance as well. Redispersible pow-ders with a hydrophobic effect are normally used to achieve all requirements of a tilegrout. They reduce the risk of efflorescence as well as staining of the grout. The stan-dards in the US and Europe are summarized in Tab. 13-3.

The fields of ceramic tile mortars and tile grouts are certainly the most developedfor redispersible powders in cementitious applications. The use of redispersiblepowder improves adhesion bond strength to all types of substrates, the deformabili-ty (flexibility), the cohesive and flexural strength, the open time the wetting capabili-ty as well as the workability within dry mix mortars.

Fig. 13-8 Adhesion of ceramic tile adhesives to different substrates.


13.4.3

Exterior Insulation and Finish Systems and Top Coats

With the beginning of the 1970s exterior insulation and finish systems (E.I.F.S) wereused in Germany. (E.I.F.S. is predominantly used in North America. The abbrevia-tion used in Europe is ETICS – exterior thermal insulation compounds.) The first oilcrisis in Germany 1973 together with financial support of the government for home-owners had helped tremendously to promote the system. Some of the advantages ofE.I.F.S. are saving energy, healthier climate condition inside the house, less dam-ages of facades and possible savings at the over all building costs. Between 1973 and1993 approximately 300 million square meters of E.I.F.S. were applied on facades inGermany. As a consequence more than 18 billion liters of oil were saved (approxi-mately 113 million barrels). This also means considerably less CO2 was released intothe atmosphere, that also emphasizing a positive environmental aspect of E.I.F.S.

After Germany, the country with the most usage of E.I.F.S. is the United States.However, the use of E.I.F.S. in the past within the United States has been more foroptical reason. Recently more and more the energy saving aspect of the system hasbecome a more considered aspect for homeowners. In both countries, organizationsexist representing the E.I.F.S. industry and its interest: representative of Germany isthe “Fachverband Waermedaemm-Verbundsysteme” and of the USA the “ExteriorInsulation Manufacturer Association, EIMA”.

The technology used in both countries is predominantly based on the usage ofpolystyrene as an insulating material. In the early 1970s, the materials for E.I.F.S. of-fered in Germany were shipped to a construction site as ready to use systems (pastyconsistency). They had to be mixed with cement before usage. Mistakes occurred bynot meeting the polymer cement ratio according to the manufacturers’ requirement,resulting in damages and complaints. The industry shifted almost completely to drymix systems in order to avoid the mentioned problems. The use of machines alsopromoted dry mix mortars modified with redispersible powders. The time and costsavings remain tremendous. In the US, reliability and control over the formulationout of production as well as time and cost savings of machine applicable systems,

Tab. 13-3 EN and ANSI standards for tile grouts.

European standards*EN 12808-1 Determination of chemical resistanceEN 12808-2 Determination of abrasion resistanceEN 12808-3 Determination of flexural and compressive strengthEN 12808-4 Determination of shrinkageEN 12808-5 Determination of water absorptionEN 12002 Determination of deformability

US standardsANSI A 118.6 Specification for standard cement grouts for tile installationANSI A 118.7 Specifications for polymer modified cement grouts for tile installation

* There is also a draft of “Tile grout mortars for tiles, definitions and requirements”


has clearly set the trend over the last 5–10 years towards more and more usage of thedry mortar technology and, therefore, towards redispersible powders/polymers.

Because of the use of redispersible powders, the application of E.I.F.S. has reachedsuch a high level of reliability and quality consistency that manufacturers in Ger-many normally allow a 30-year warranty for their systems. So far this level of war-ranty is not yet achieved in the US.

In Europe, as well as in the US several technical tests are conducted in order toprove the performance of E.I.F.S. under different test conditions. The testing of suchsystems is very severe. Some of the most important types of tests conducted on anE.I.F. system are:– stability and flammability,– insulation properties,– adhesion of cementitious materials on polystyrene,– water absorption,– impact resistance, and– flexural and compressive strength.

Most of the tests are still very much depending on the country (Europe). In the USthere are different authorities (regional and city codes) like the “American Society forTesting and Materials – ASTM”, the “Building Officials and Code Administrators –BOCA”, the “International Conference of Building Officials – ICBO” and the “South-ern Building Code Congress – SBCC”. Information on test procedures is also avail-able through EIMA. More specific information can be gathered through the differentorganizations. In Europe the entire E.I.F. system needs even a technical approvalgranted by testing institutes according to the “European Organization for TechnicalApproval, EOTA”. The principle layers of an E.I.F. system are shown in Fig. 13-9.

Substrates might vary. In the US it is normally plywood. Normally one will findconcrete/brick as a substrate. Right on top of the substrate the insulation board isglued with an adhesive. In addition sometimes mechanical fasteners are use as well.

1. Substrate2. EPS-Adhesive

3. EPS-Board4. Base Coat

5. Top Coat/Finish

Fig. 13-9 The principle structure of an E.I.F. system.


85 % of the insulation material used in Germany is Extruded Polystyrene “EPS”. TheEPS adhesive is normally the same material as the base coat. The functionality of thebase coat is protection and reinforcement of the EPS panel. Without polymer modi-fication there would be no adhesion of the EPS to the substrate and no adhesion ofthe base coat to the EPS panel. Besides adhesion, the right polymer modification be-comes also very important when impact resistance, water absorption or deformationcapability (flexibility) is tested. The base coat has an important functionality withinthe entire system. The right modification of the base coat with at least 3 to 6 % redis-persible powder will finally guarantee good performance values and as a conse-quence contribute to an excellent weather stability of the entire system. The integrityof the base coat, meaning a crack free base coat, is a precondition for good technicalperformance. For that purpose the polymer-to-cement ratio should be as high aspossible. This is one of the main differences between Europe and US . Normally thecement content in US systems is higher than in Europe. Assuming the polymercontent is very similar, this results in a higher polymer-to-cement ratio in Europeansystems compared to US systems. This has to do with the fact that the preference inEurope is towards more flexible system where else in the US a hard surface appear-ance of the base coat is preferred by contractors.

Certainly as important as the base coat is the topcoat for the entire system. Herewe find probably the biggest difference between, for example, Germany and theUnited States. In the US cementitious topcoats are almost not used at all. They aresynthetic, cement free systems that are very often ready to use and based on emul-sion technology. In Europe, as with Germany, topcoats are cement based as well.

Top/finish coats must meet certain critical physical and technical requirements.These include:– good adhesion to the substrate (tensile adhesion strength),– low water absorption or water repellency (hydrophobicity),– good drying characteristic (high water vapor permeability),– low susceptibility to cracking (good relaxation properties, flexibility),– the modulus of elasticity of the top coat should be lower than the modulus of elas-

ticity of the substrate (layer below),– resistance to weathering,– mechanical stability (high impact resistance),– low dirt pick up,– very low flammability.

(Finish or topcoats can also be named render, plaster or stucco. Normally slightdifferences apply, for example in thickness of the coating depending on the technol-ogy used. As far as the use of redispersible powder is concerned, they can be consid-ered equivalent.)

The addition of organic polymeric binders in form of redispersible powders tomineral plasters and stuccos can significantly enhance certain properties, such asadhesion to the substrate, mechanical resistance, low water absorption (hydrophobiceffect by using special redispersible powders) and long-term durability. In order tomeet these requirements the preferred redispersible powders used in topcoats arevinyl acetate/ethylene copolymers. Especially when it comes to flammability vinyl


chloride containing systems perform the best closely followed by vinyl acetate ethyl-ene containing polymers. Topcoats/E.I.F.S based on acrylics and acrylates, likestyrene acrylics, perform the worst in this respect.

The addition of approximately 0.5 to 2 % special hydrophobic redispersible pow-ders to dry mortars additionally imparts uniform water repellency throughout with-out effecting the water vapor permeability.

Mineral topcoats are composed of lime and cement as mineral binders, aggregates(fillers like silica sand), pigments and additives, such as cellulose ethers, starchethers, lightweight fillers, fibers, thickener, hydrophobic agents, wetting agents andsometimes even surfactants. With the exception of any mineral binder this list applies also to synthetic topcoat which are almost exclusively used in the US. Table13-4 shows some of the specifications for topcoats in Europe (Germany) and the US.

One aspect that is very important to the E.I.F.S. industry as well as to topcoat man-ufacturers is certainly the hydrophobicity of their base coats and/or topcoats.

What is the mechanism behind a hydrophobic effect achieved by using a hy-drophobic redispersible powder?

When water is added to the dry mix topcoat, the polymeric binder in the form of aredispersible powder is very quickly redispersed. Then the polymer particles accu-mulate mainly in the pores, forming a film that coats the pores without actuallyblocking them [6–8]. Because the pores (capillaries) are coated with a water repellentpolymer film with good adhesion to the cement, the capillary water absorption is re-duced. Thus a permanent effect is achieved throughout the mortar. If the amount ofredispersible powder stays within 3 to 6 % there is no loss of water vapor permeabil-ity. This, of course, depends also very much on the hydrophobicity of the used redis-persible powder. Because of the mentioned adhesion of the polymer to the cementpores the adhesion as well as the flexural strength and toughness of the material isimproved also. Scanning electron micrographs are shown in Fig. 13-10 and demon-strate the formation of the polymer film within the cement matrix.

The SEM technology was also used to demonstrate that the redispersible powderscontinue to fulfil their functionality over an extended period of time. This is alsoshown by experiments to determine physical factors such as water absorption andwater vapor permeability on defined test specimen after long-term exposure to out-door weathering conditions. Figure 13-11 shows the capillary water absorption of testspecimen after up to 6 years outdoor exposure at different polymer levels.

Tab. 13-4 Specifications for topcoats.

German-US standardsDIN 18555/ASTM C 109 Compressive strengthDIN 18555-6/* Tensile bond adhesionDIN 52617/ASTM C 413 Water absorptionDIN 52615/ASTM E 96 Water-vapor permeabilityDIN 18555/ASTM C 231 Air contentDIN/EN 196/ASTM C 580 Flexural strength

*ASTM E 2134-01 for E.I.F.S.


13.4.4

Self-leveling Underlayments

The area of self-leveling underlayments (SLU) is out of a technical perspective prob-ably the most complex one if it comes to applications of redispersible powders. On agiven uneven substrate (i.e. screed or surface to be refurbished), self-leveling mor-tars have to provide a suitable, smooth and solid substrate in order to apply all kindof flooring materials like carpets, wood parquet, PVC, tiles etc. Self-leveling under-layments should be applicable in an easy and efficient manner, even for large areas.

Fig. 13-10 SEM of polymerfilm in cement matrix.

Fig. 13-11 Long-term performance of cementitious topcoats.

Capillary water absorption of mineral topcoat - long term exposure

0

0.5

1

1.5

2

2.5

3

3.5

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0.5% 1.0% 2.0% 3.0% 3.5%

percentage redispersible powder on total formulation

wat

er a

bso

rpti

on

co

effi

cien

t ac

cord

ing

to

DIN

526

17

21 days standard conditions 1 year outdoor exposure 6 years outdoor exposure


Therefore, the SLU material has to have very good flow characteristics, self-levelingand self-smoothing properties. In addition, it should perform fast setting/drying,saving time and thus the floor surface can be applied after only a few hours. The SLUmaterial should adhere to all kind of substrates, provide low shrinkage, high com-pressive strength and abrasion resistance.

The technical requirement of a SLU reaches from very simple to highly sophisti-cated products. They vary in thickness from a very thin layer of 1–10 mm (1/25–2/5inch) (feather finish, self-leveling/troweling mortars and underlayments), up to 60mm (approx. 2.5 inch) for self-leveling screeds, which are always applied by ma-chines (mixing and pumping in one set up). The set time (“walk over time”) of thesematerials changes from normal/regular setting to very fast setting products. Nor-mally this is a question of the requirement of a specific job, allowing putting downthe floor above the SLU in a certain time frame. The shorter the setting/drying time,the thicker the mortar is applied, the more complicated and expensive the formula-tion becomes. Self-leveling compounds (underlayments and screeds) are based onspecial hydraulic binders like Portland cement (OPC), high alumina cement (HAC)and gypsum (anhydrite), in order to achieve fast curing and drying by avoiding ex-cessive shrinkage or expansion.

So far there are no standards on self-leveling underlayments (SLU) in Europe orthe U.S. However, the techniques and the application is very well known for manyyears. Polymer modification is absolutely necessary within this technology, since therequirements are very sophisticated. According to their use and the specific require-ments, SLUs are polymer modified by 1–10 % of redispersible powder calculated ontotal formulation. Standard products are normally modified between 2 and 4 %,highly modified mortars are mainly used for refurbishment of wooden flooringswith self-leveling compounds. The redispersible powder increases the adhesion to allkind of substrates, decreases the internal stresses (reduced crack formation and highabrasion resistance), improves the flexural strength, elasticity and the abrasion re-sistance. Special powder grades will also support the self-leveling and self-flowingcharacteristics of the mortar. Figure 13-12 shows the results of an abrasion test for aself-leveling compound with and without modification with a redispersible powder.Depending on the dosage of the redispersible powder, the abrasion resistance can bereduced significantly. This becomes especially than very interesting, when the SLUis also used as a wearing surface in an overlayment application.

13.4.5

Patch and Repair Mortars

Concrete is a very versatile, long-lasting and durable building and construction ma-terial if it is applied according to the state of the art. In the past, and even today,unfortunately, repeated disregard of the fundamental principles of concrete andstructural concrete application has lead, and, in many cases, still leads to severe andserious damage in the building industry. The cost of the repair of concrete structureshas dramatically increased over the last 30 years in all industrial countries. In Ger-


many approximately 20 % of the cost of the volume of structural concrete work is at-tributed to the repair and maintenance of existing buildings and structures.

The degradation of structural concrete is caused by corrosion of the steel rein-forcement due to chemical processes, which often occur over a long period of time.One of the main reasons is the carbonation of concrete. Acidic carbon dioxide (CO2)from the atmosphere and other aggressive media (such as SO2, acid rain) neutralizesthe alkalinity of the concrete. Once the alkaline environment of the steel reinforcingno longer exists, the steel starts to corrode and, due to its volume increase, causessplitting of the concrete on top of the steel reinforcement. A secondary cause of cor-rosion is the penetration of free chloride ions into the concrete, leading to chlorideion attack on the steel.

Fig. 13-12 Abrasion resistance with and without redispersible powder.


In the construction industry concrete repair work can be classified in two types:– concrete repair, which does not contain steel reinforcement and which does not

have load-bearing functions. The repair is normally done for aesthetic reasons(cosmetic repair work) only, with namely patching mortars/compounds

– repair and reconstruction of damaged reinforced and load-bearing concrete struc-tures, in order to maintain and reconstitute their structural stability. This is donein stages with different kind of mortars, which are part of a “concrete rehabilita-tion system” (typical applications: repair work and rehabilitation of bridges, park-ing decks, tunnels, etc).Patching mortars for re-profiling and cosmetic repair are mainly based on dry mix

mortars and are not part of an entire repair or rehabilitation system. Usually, ce-ment-based mortars are used for indoor and outdoor applications, whereas gypsum-based products are only used for some specific indoor applications (cosmetic repair).Patching mortars are used to repair defective or damaged areas of mineral surfaceswithout taking on a load bearing function, i.e. for filling small holes, voids, cracksand cavities in order to restore the original dimension. Typical applications arepatching mortars for walls, ceilings, floors, steps of staircases, etc. These mortarsmust have the following characteristics:– good workability,– easy to apply,– good adhesion to all construction substrates,– high durability and abrasion/wear resistance, if exposed to direct wear/load,– sufficient flexibility to reduce the risk of crack formation,– low shrinkage, and– water repellence for outdoor applications.

To meet the required technical criteria, these patching mortars are applied as apolymer modified pre-packed dry mix mortar. Polymer modification with redis-persible powder will – depending on the dosage – improve the:– workability of the mortar,– wetting capability of the substrate,– adhesion to all kind of substrates,– flexural strength,– abrasion resistance,– flexibility (lower modulus of elasticity than substrate),– durability, and– water repellent effect by using special grades of hydrophobic redispersible pow-

ders.To be able to guarantee the durable and reliable repair of structural concrete, three

main fundamental requirements of a concrete rehabilitation system must be ful-filled simultaneously:– restoration of the corrosion protection of the steel reinforcement (alkaline envi-

ronment),– restoration and re-profiling of the concrete structure including its load-bearing

functions, and


– restoration of the durability of the whole construction (protection against weather-ing and environmental damage caused by CO2, SO2, Cl2, salts, etc.).Today, polymer modified cement concrete (PCC) mortars, which can be applied by

hand, in a wet or even a dry spraying process, are usually used for the rehabilitationof concrete structures. Different kind of mortars with different characteristics andfunctions are used as the components for concrete rehabilitation systems:– primer and adhesion promoter for the reinforced steel (polymer modified cemen-

titious slurry or epoxy based coating materials),– adhesion promoter slurry (primer or key-coat) for the concrete to be repaired (poly-

mer modified cement based slurry),– restoration and re-profiling mortar (polymer modified cement based mortar),– fine stopper or smoothing mortar (polymer modified cement based mortar con-

taining fine aggregate), and– protection and finish coat (dispersion paints, crack over bridging paints, cementi-

tious waterproofing sealing slurries, etc.).The improvement of adhesion to concrete and steel, using a polymer modified re-

profiling mortar, with and without applying a cementitious primer, is demonstratedin Fig. 13-13; Fig. 13-14 shows the improvement in flexural strength of a typical re-profiling mortar applied by hand with and without different grades of redispersiblepowder.

The flexural strength of the mortar is already significantly improved by addingonly 2 % of redispersible powder without affecting the compressive strength toomuch.

Fig. 13-13 Adhesion to concrete and steel with and without primer.

Tensile bond adhesion after 28 d standard conditions polymer/cement ratio = 0.07

0

0.5

1

1.5

2

2.5

3

over concrete over steel

Ten

sile

ad

hes

ion

[N

/mm

2]

without primer with primer


Almost the same improvements are obtained by applying the repair mortarthrough a dry shotcrete process. Within this process the water is mixed with the drymortar only in the jet. After that the mixed mortar is immediately sprayed onto thesurface. Despite this extremely short mixing and almost no slake time, the redis-persible powder redisperses quickly and completely enough in order to improve thetensile adhesion strength and the flexural strength in almost the same magnitudecompared to a conventional application by hand.

13.4.6

Waterproof Membranes

Water in liquid or in vapor form is the most destructive weathering element forbuilding constructions, like concrete, masonry, and natural stone structures. Water-proofing and damp-proofing techniques are used to preserve a structure’s integrity,functionality and usage throughout its lifetime. For preventing all possible water in-trusions, the exterior of a building has to be protected form top to bottom with wa-terproofing materials. Exterior parts of a building could be classified in roof coating,below-grade waterproofing materials, which are materials to prevent surface- andground water or water under hydrostatic pressure from entering into a structure.Typically metal and plastic films, cementitious waterproofing sealing slurries and bi-tuminous waterproofing systems are used for that type of application. Above-gradewaterproofing materials, which prevent water intrusion into exposed structure ele-ments, could be categorized into:

Fig. 13-14 Flexural strength improvement by use of redispersible powders.

Flexural strength of repair systems modified with different redispersible powders and applied by different techniques

0

2

4

6

8

10

12

14

shotcrete spray applied hand applied

Fle

xura

l Str

eng

th [

N/m

m2]

no polymer redispersible powder 1 redispersible powder 2 redispersible powder 3


– decorative and finishing barrier systems, i.e. all kinds of paints;– mineral topcoats (renders, plasters);– damp-proofing materials, which reduce or prevent water vapor transmission

through building materials and are not subjected to weathering or water pressure(water vapor barrier foils); and

– flashings, materials or systems installed to direct water entering through the wallcladding back to the exterior like metal foils in walls to prevent capillary water up-take.All waterproofing has to be part of a whole system and must interact integrally to

reach complete effectiveness and to prevent water infiltration. In case one of thesesystem parts fails or does not perform with all other protection systems, leakage willoccur. Adequately controlling groundwater, rainwater and surface water, as well asthe transport of humidity in the form of water vapor will avoid unnecessary repairs tobuilding’s exterior or its damage or even destruction (deterioration). Apart from pro-tecting the exterior of building constructions, there is a multiplicity of waterproofingmaterials for interior use. Some of the waterproofing materials are used to protectagainst the detrimental action of aggressive substances like salts and acids transport-ed by the water.

Traditional sealing and waterproofing systems, i.e. according to the German stan-dard DIN 18195, include bituminous materials, plastic waterproofing foils and met-al tapes for interior and exterior applications. Different types of materials can beused in order to seal and protect the surface of buildings or its structural compo-nents against the intrusion of dampness and water. Nowadays products for that pur-pose are based on reactive resins like epoxy and/or polyurethane, dispersions(paintable waterproofing membranes) and mineral binders like cement, which areknown as waterproofing membranes or sealant slurries.

Cementitious waterproofing membranes have been successfully used for morethan 40 years in Europe for protection of a wide range of building structures andstructural components. The structures were either exposed to periodically or long-term wettings (surface water, seepage water), low hydrostatic pressure (soil damp-ness) or in combination with appropriate engineering even high hydrostatic pres-sure. Cementitious membranes (slurries) are used to waterproof wet rooms andwater tanks, and due to their excellent weathering resistance they are also used forexterior surface protection. Further typical applications are the sealing and water-proofing of basement walls, swimming pools, walls and floors, in bathrooms, on bal-conies and porches (as a waterproofing layer to be tiled over). Especially in the case ofa tile application these slurries can also act as crack isolation membranes. In addi-tion, flexible, cementitious waterproofing membranes are often used as a protectivesurface-coating system for structural concrete (i.e. protection of reinforced structuralconcrete within new structures as well as for concrete structures after restoration). Itis applied for the protection against penetration of water, chlorides and free carbondioxide in order to avoid corrosion of the reinforcing metal and can provide a protec-tive layer to a building against aggressive chemicals (sulfates, acids, i.e. in waste-wa-ter drains). Some of the advantages of cement-based waterproofing membranes are:


– excellent resistance against water, even if exposed permanently;– excellent resistance against long term weathering;– good scratch resistance;– good load-carrying capacity; and– much higher water vapor permeability compared to most of the other systems.

Consequently there are no problems with blistering since water vapor passesthrough the membrane.Cement-based waterproofing slurries are easy to use, non toxic, provide a fully

bound and monolithic surface without joints and can be easily applied on substrateswith complex surface shapes. In contrast to other systems, cementitious waterproof-ing slurries can even be used on damp and wet mineral surfaces. Their physicalproperties are also less temperature dependent compared to bitumen based materi-als.

Simple, non-polymer modified cement based slurries are still used for the protec-tion against surface water, but they are not suitable to seal against water under hy-drostatic pressure. In order to improve the poor adhesion, the poor water tightness,and the extremely low deformability or flexibility of these non modified systems,polymers are added in form of liquid dispersions on the job-site or in form of a re-dispersible powder already mixed in the dry mix mortar. The use of special additivesin the dry mix mortars like water retention agents, thickening agents and rheologicaladditives in combination with the polymeric binder, the redispersible powder, pro-vide an excellent workability and make sure that there is no need for a post water-treatment of the applied slurry.

Today, in principle, two different systems of cementitious waterproofing mem-branes or slurries are available:1. Standard or rigid mineral waterproofing slurries, which are polymer-modified,

pre-packed dry mix mortars containing approx. 3 to 6 % of redispersible powder.They are used for mineral substrates, which are stable, sound and solid. Thereshould be no risk for crack formation, movements or dimensional changes likeshrinkage.

2. Flexible and highly flexible cementitious waterproofing slurries (as two-compo-nent or one-component systems).In addition to the traditional, rigid waterproof membranes, developments in the

late 1970s led in Europe to flexible waterproofing slurries, which are to a certain ex-tend capable to over-bridge small cracks (up to approx. 1 mm) in the substrate. Theflexibility of such products strongly depends on the polymer/cement ratio and cer-tainly also on the flexibility of the polymer itself. Flexible and highly flexible water-proofing cementitious slurries are used on substrates still undergoing shrinkage, vi-brations, movements, stresses, crack formation and on substrates difficult to be coat-ed like wood, steel, aerated light weight blocks and gypsum. Due to their high poly-mer content (up to 25–40 % on total formulation), they are diffusion and chemicallyresistant against chloride, sulfate ions and carbon dioxide or other aggressive mate-rials.

Thus far these flexible cement based waterproofing, sealing slurries have beenmainly used as two-component systems (liquid dispersion/emulsion added to the

13.5 Summary 353

pre-packed dry mix). But due to the many disadvantages of modifying mortars withliquid dispersions on a job-site, in modern construction technique more and morethe one-component, flexible cementitious slurries, modified with high dosages ofspecial redispersible powders are used. These one-component, premixed polymer-modified dry mix mortars are offering advantages as they were already discussedwithin this chapter.

13.5

Summary

The need for new construction methods and building materials, that are safely, reli-ably, efficiently and economically to apply, promotes modern technologies like the“dry mix mortar technology”. Redispersible powders make the production of com-plete pre-manufactured high quality mortars (“bagged mortars”) possible. As a con-sequence, job-site mix technology and job-site modification of mortars with liquidpolymers is being replaced all over the world. Especially since product characteristicscan be specifically designed for modern construction requirements and climate con-ditions by using dry mix mortars.

Dry mix mortars modified with redispersible powders provide a significantly im-proved productivity on the construction site. They allow a high degree of rationaliza-tion coupled with an easy, rapid, more efficient and safer handling and processing ofthe product. This eliminates onsite mixing errors and ensures, consistently, excel-lent results. The quality of the workmanship is consistent on a high level thus im-proving the warranty status of a construction job dramatically.

Dry mix mortars, mainly based on cement but also on gypsum, that are modifiedwith redispersible powders have been successfully used for many decades all overthe world. The most typical applications are:– ceramic tile adhesives,– tile grout mortars,– mortars for the thermal insulation systems,– stuccos, skim-coats and finishing renders,– patch and repair mortars,– self-leveling under- and overlayments,– waterproofing sealing slurries (membranes),– joint compounds, and– powder paints.

The modification of dry mix mortars with dry polymers in the form of redis-persible powders also significantly improves the technical performance of the mor-tars. The combination of the mineral binder with a polymeric binder in the form ofan redispersible powder in dry mix mortars guarantees outstanding synergistic prop-erties and characteristics, which cannot be achieved by either of the binders alone.The sufficient modification of mineral dry mix mortars by redispersible powders willimprove workability, adhesion to various substrates, flexibility and deformability of


the mortars, abrasion resistance, density (impermeability), flexural and cohesivestrength and the long-term durability.

Manufacturers, contractors, applicators and end-users (“Do it yourself” market) allbenefit significantly from dry mix mortars modified with redispersible powders.That technology almost exclusively makes machine applications, which becomemore and more popular with all kinds of construction materials, possible.

References

1 Research report No. 13 of “Vereinigungvon Systembouwers van de WerkgroepSA 5, Tegels, Het vermijden van Schadeaan gelijmd Wandtegelwerk”; March1975, Vereinigung von Systembouwers,Gravenhage, Netherlands.

2 Publications of G. Wesseling (TNO Insti-tute, Netherlands); in TonindustrieZeitung No. 8 1971, 95, 211.

3 Research report B II 5 – 800177-118; “Ermittlung des Verformungsverhaltensvon Duennbettmoerteln bzw. Klebstof-fen fuer keramische Fliesen”; August1979 von Prof. Dr. Kirtschig; TechnischeUniversitaet Hannover.

4 Rapport “Lim for keramiske fliser; methode for proving av even tile aoverfore relative bewegelser mellomunderlag og fliser (flexksibilitet)” von BYGGFORSK, Norwegisches Baufor-schungsinstitut, Forskningsveien 3 b;Postboks 123 Blindern, 0314 Oslo 3,Projekte E 3593, Trondheim04/08/1992.

5 Fox T.J.; Bull. Am. Phys. Soc. 1956, 1, 23.6 Schulze, J.; Tonindustrie-Zeitung 1985,

109, 698. 7 Schulze, J.; Beton 1991, 5, 232.8 Adler, K.; Schweizer Baublatt 1988, 31,

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