Flat roof waterproofing systems based on liquid products
Experimental characterization of the systems’
mechanical performance
João Luís Garcia Feiteira
Extended abstract
Supervisor: Jorge Grandão Lopes
Co-supervisor: Jorge Manuel Caliço Lopes de Brito
November 2009
Flat roof waterproofing systems based on liquid products
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1. Introduction
Due to the slow drainage of accumulated rainwater, flat roofs require a waterproof coating [1].
Traditionally, for more than 100 years, this coating has been made of bituminous material
applied either as a built-up roofing system or as a membrane sheet. However, other
waterproofing materials have been available for decades.
Liquid applied roof waterproofing systems (LARWSs) include, in addition to bituminous systems,
systems based on less well-known waterproofing materials such as polyester, polyurethane and
water dispersible polymers.
LARWSs offer some advantages over membrane sheets. Applied like paint or with the help of a
spatula, they form an adhesive, seamless waterproof coating over practically any surface or
shape. Thus, both the possibility of water migrating beneath the coating and the need to treat
laps and seams are eliminated [2].
LARWS requirements and their methods of verification are established by the European
Organization for Technical Approvals (EOTA). Resistance to mechanical damage, especially
perforation, is one of the most important requirements set out in the relevant EOTA guide, the
ETAG 005 [3]. ETAG 005 also links LARWS resistance to perforation to the recommended
accessibility and frequency of traffic envisaged for the roof on which it is to be applied.
The scope of this study includes determining LARWS resistance to static and dynamic
indentations, tensile properties, fitness for intended use and flexibility at low temperature.
2. Materials and method
Free-standing samples were prepared from some of the LARWSs available on the Portuguese
market. In order to evaluate the influence of the number of coats and reinforcements on
mechanical resistance, in the case of most systems samples were obtained from different
formulations, as shown in Table 2.1. All the samples were prepared according to the
manufacturer’s instructions and dried under the conditions specified in ETAG 005, at a
temperature of 23 ºC and relative humidity of 50%. The reinforcement layers used (Table 2.2)
were as prescribed by each LARWS manufacturer.
Systems of different materials with similar thicknesses immediately after installation do not
necessarily produce coatings with similar thicknesses after drying. Thus, although desirable,
similar film thicknesses for comparable coatings could not be assured. The number of coats
(applying the quantity per coat prescribed by the manufacturer) was used instead to generate
comparable coatings and their thickness was determined by means of a digital comparator with
a 6 mm diameter cylindrical tip, so that stable readings could be obtained.
Extended abstract
2
Table 2.1 – LARWSs tested
Material Mass per
unit volume (g/cm3)
Reinforcement layer
Number of coats
Total quantity (kg/m2)
Minimum drying time
(days)
Mean dry sample
thickness (mm)
- 2 3,47 2.32 2 4,56 2.43 Two-
component cementitious
1.35 Fibreglass mat (4 mm mesh; 200
g/m2) 3 6,33 21
3.62
- 2 2,93 1.50 2 3,61 1.23 Acrylic 1.45 Fibreglass mat (2
mm mesh; 60 g/m2) 3 4,38
21 1.80
2 2,66 1.21 Fibrous acrylic 1.40 - 3 4,09 21 1.91 Partially
bonded two-component
cementitious
1.45 Unidentified fleece (90 g/m2) 2 2,18 21 1.62
- 2 2,70 1.44 2 2,52 1 1.52 Liquid silicone 1.3 Polyester fleece
(50 g/m2) 3 3,93 2 2.38 - 2 0,99 0.72
2 0.97 0.67 Liquid rubber 1.2 Polyester fleece (50 g/m2) 3 1,45
4 1.00
Polyurethane 1.43 - 2 2,74 5 1.37
Table 2.2 – Reinforcement layers used
Reinforcement layer Mass per unit area (g/m2)
Maximum tensile force
(N/50 mm)
Elongation at maximum tensile
force (%) Fibreglass mat (2 mm mesh) 60 660 3 Fibreglass mat (4 mm mesh) 200 1935 4
Unidentified fleece 90 110 50 Polyester fleece 50 150 22
Each system was tested for the following properties:
watertightness, using the method described in the EOTA Technical Report (TR) 003
[4]; a 1m hydrostatic head of water was applied to the exposed side of the test
specimens and, after a period of 24 h, these were inspected for signs of leakage;
resistance to dynamic indentation (impact) according to TR 006 [5]; this method
requires a fixed impact energy of 5.9 J to be applied to LARWS test specimens by
means of a cylindrical steel indentor with a given diameter; each diameter being
linked to a level of performance, as shown in Table 2.4;
resistance to dynamic indentation (impact) according to EN 12691 [6]; this method
was used to further differentiate between resistance to this type of mechanical
damage in the LARWSs being tested; in this case, test specimens were struck by a
drop mass of 500 g using a 12.7 mm diameter spherical puncturing tool;
resistance to static indentation (impact) according to TR 007 [7]; a load is applied to
a 10 mm steel rod with a hemispherical end resting on the exposed side of the test
Flat roof waterproofing systems based on liquid products
3
specimen; each of the four defined loads is linked to a level of performance, as
shown in Table 2.5;
tensile properties according to EN 12311-1 [8]; test specimens are clamped in the
grips of a tensile testing machine capable of maintaining a uniform rate of
separation and the values for the maximum tensile force and corresponding
elongation are registered;
flexibility at low temperature according to EN 1109 [9]; after being kept at 5 ºC for 1
h, test specimens were bent over a cylindrical shape with a diameter of 30 mm until
a 180º angle was reached between the ends of the specimens; after being bent, the
test specimens were visually inspected for cracking.
Table 2.3 shows the number of test specimens per system used in each test. For dynamic
indentation tests made according to TR 006, only 3 of the 5 specimens assigned to dynamic
indentation were used. For reinforced coatings, EN 12311-1 requires that 10 specimens be
tested; 5 of them taken from the longitudinal direction of the reinforcement layer and the other 5
from the transverse direction.
Table 2.3 – Number of test specimens
Test Number of specimens Dimensions (mm) Watertightness 3 200 x 200
Dynamic indentation 5 200 x 200 Static indentation 3 200 x 200
Tensile properties – unreinforced system 5 300 x 50 Tensile properties – reinforced system 5 + 5 300 x 50
As prescribed in ETAG 005, each LARWS should be included in one of four user load
categories, defined in Table 2.6, with a corresponding recommended accessibility and
frequency of traffic envisaged for the roof on which it is to be installed.
It should be noted that absolute categorisation of a LARWS according to user load requires
further testing of its resistance to ageing media and the effects of low and high surface
temperatures. In addition, as all the tests were carried out on free-standing test specimens, the
influence of substrate adhesion on the coating’s resistance to perforation was not taken into
account.
Table 2.4 – Levels of resistance to dynamic indentation
Level of resistance I4 I3 I2 I1 Diameter of indentor (mm) 6 ± 0.05 10 ± 0.05 20 ± 0.05 30 ± 0.05
Table 2.5 – Levels of resistance to static indentation
Level of resistance L1 L2 L3 L4 Load (N) 70 ± 1 150 ± 1 200 ± 1 250 ± 1
Extended abstract
4
Table 2.6 – Relationship between user load category and indentation levels of resistance
Minimum level of resistance User load category Dynamic indentation Static indentation Examples of accessibility
P1 I1 L1 Non-accessible
P2 I2 L2 Accessible for maintenance of the roof only
P3 I3 L3 Accessible for maintenance and to pedestrian traffic
P4 I4 L4 Roof gardens, inverted roofs, green roofs
3. Results and discussion
3.1. Watertightness After 24 h, only the 2-coat reinforced liquid rubber based coating showed signs of leakage. The
fact that the unreinforced and the 3-coat reinforced liquid rubber based coatings remained
watertight during the test shows that this was caused by not using a sufficient amount of
waterproofing material to cover the fleece used as reinforcement.
When dealing with a LARWS with a low recommended quantity per coat (less than 1 kg/m2),
care must be taken that, if used, the reinforcement layer is adequately covered.
As it did not satisfy the essential requirement of a waterproofing coating – that it should be
waterproof - no further tests were done on the 2-coat reinforced liquid rubber based coating. All
the other coatings tested were considered watertight.
3.2. Resistance to dynamic indentation The results (Table 3.1) show that resistance to impact in all the systems complies with their
intended use. All but the silicone based systems reached the highest level of resistance
prescribed in ETAG 005.
The test method described in EN 12691 allowed for further differentiation of resistance to this
kind of mechanical damage.
Figure 3.1 shows the performance of comparable unreinforced coatings based on 2 coats of
different materials. Even though most coatings reached the highest resistance level when tested
under the TR 006 method, in this case the results revealed a distinct performance gap between
systems of different materials.
While the performance of acrylic, cementitious and polyurethane based coatings was similar,
the fibrous acrylic coating showed a significant (50%) relative decrease in resistance to dynamic
indentation. There was also evidence of a much higher susceptibility to perforation in liquid
silicone and liquid rubber based coatings, when compared to all the other coatings tested.
The fact that the 2-coat unreinforced cementitious coating had a significantly higher film
thickness than all the other unreinforced coatings has to be taken into account when judging its
performance. The same resistance to impact (0.70 m) was achieved by acrylic and
polyurethane based coatings with much lower thicknesses.
Flat roof waterproofing systems based on liquid products
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Table 3.1 – Resistance to dynamic indentation test results
Material Reinforcement layer Number of coats
Minimum diameter of
indentor (mm)
Maximum drop height
(m) - 2 6 0.70
2 6 1.00 Two-component cementitious Fibreglass mat (4 mm
mesh; 200 g/m2) 3 6 ≥ 2.00 - 2 6 0.70
2 6 0.60 Acrylic Fibreglass mat (2 mm mesh; 60 g/m2) 3 6 0.90
2 6 0.35 Fibrous acrylic - 3 6 0.90 Partially bonded two-
component cementitious
Unidentified fleece (90 g/m2) 2 6 0.50
- 2 10 0.05 2 10 0.10 Liquid silicone Polyester fleece (50
g/m2) 3 10 0.10 - 2 6 0.15
2 - - Liquid rubber Polyester fleece (50 g/m2) 3 6 0.30
Polyurethane - 2 6 0.70
- Test not performed
0
0,2
0,4
0,6
0,8
Acrylic
Fibrous acry
lic
Cementitious
Liquid silico
ne
Liquid rubber
Polyurethane
Max
imum
dro
p he
ight
(m)
Figure 3.1 – Resistance to dynamic indentation test results for 2 coats of unreinforced LARWS
0
0,5
1
1,5
2
Reinforcedacrylic
Unreinforcedfibrous acrylic
Reinforcedcementitious
Reinforcedliquid silicone
Max
imum
dro
p he
ight
(m)
2 coats3 coats
Figure 3.2 – Resistance to dynamic indentation test results for 2 and 3-coat LARWSs
Extended abstract
6
Comparison between 2 and 3-coat based coatings (Figure 3.2) shows that, as expected, a
greater film thickness can lead to greater resistance to impact. The results also showed that this
parameter was most influential in resistance to impact in fibrous acrylic and cementitious
coatings, which, incidentally, were the stiffer materials. The 3-coat reinforced cementitious
coating reached the 2 m maximum drop height of the testing machine.
The use of a reinforcement layer led to greater resistance to impact in 2-coat cementitious and
liquid silicone based coatings. With the acrylic coating, reinforcement lead to a 0.10 m decrease
in resistance. This was linked to the lower thickness of the 2-coat reinforced acrylic sample,
when compared with the unreinforced sample.
3.3. Resistance to static indentation Static indentation tests confirmed the greater resistance to perforation in the cementitious and
polyurethane based coatings, as shown in Table 3.2. The results also showed a significant
performance gap between dynamic and static indentation resistance in acrylic coatings. While
acrylic coatings had a similar dynamic indentation resistance to cementitious and polyurethane
based coatings, only the fibrous type of this coating reached the minimum static indentation
resistance requirement prescribed in ETAG 005. Out of all the other coatings tested, only the
reinforced silicone based coatings reached the minimum level of resistance, which confirmed a
high susceptibility to perforation in liquid silicone and liquid rubber based coatings.
Table 3.2 – Resistance to static indentation test results
Maximum resistance level (N) Material Reinforcement layer Number of
coats 70 N
150 N
200 N
250 N
- 2 ● 2 ● Two-component
cementitious Fibreglass mat (4 mm mesh; 200 g/m2) 3 ●
- 2 X 2 X Acrylic Fibreglass mat (2 mm mesh;
60 g/m2) 3 X 2 ● Fibrous acrylic - 3 ●
Partially bonded two-component
cementitious Unidentified fleece (90 g/m2) 2 ●
- 2 X 2 ● Liquid silicone Polyester fleece (50 g/m2) 3 ●
- 2 X 2 - Liquid rubber Polyester fleece (50 g/m2) 3 X
Polyurethane - 2 ●
● Maximum resistance level X Coating did not reach minimum resistance level - Test not performed
Flat roof waterproofing systems based on liquid products
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An extra coat had no significant influence on resistance to this type of mechanical damage.
None of the 3-coat reinforced coatings tested reached a higher level of resistance than the
corresponding 2-coat reinforced coatings.
The use of a reinforcement layer allowed all the 2-coat coatings to reach one higher level of
resistance and thus had a clear influence on LARWS performance in terms of static indentation.
3.4. Tensile properties Tensile test results (Table 3.3) confirmed what had already been expected from handling test
specimens of different LARWSs.
Unreinforced liquid silicone and polyurethane based coatings were much more deformable than
all the other coatings tested, as shown in Figure 3.3, with the latter being much stiffer. The
elongation values were limited to 200%, the maximum course of the tensile testing machine.
Out of all the other unreinforced coatings, the acrylic coating was still considerably more
deformable, the fibrous acrylic coating was the stiffest and the liquid rubber based coating had
the least resistance of all.
Table 3.3 – Tensile properties of LARWSs tested
Maximum tensile force (N/50 mm)
Elongation at maximum tensile force (%) Material Reinforcement
layer Number of coats Mean value Standard
deviation Mean value
Standard deviation
- 2 75 7 25 5 2 1855 290 5 0 Two-
component cementitious
Fibreglass mat (4 mm mesh;
200 g/m2) 3 2145 152 5 0
- 2 80 10 87 7 2 795 52 4 0 Acrylic Fibreglass mat
(2 mm mesh; 60 g/m2) 3 935 57 5 0
2 160 12 12 1 Fibrous acrylic - 3 295 17 13 1
Partially bonded two-component
cementitious
Unidentified fleece (90
g/m2) 2 385 8 49 1
- 2 ≥35 * ≥196 * 2 220 29 31 6 Liquid
silicone Polyester fleece (50
g/m2) 3 270 21 40 2
- 2 35 3 25 9 2 - - - - Liquid rubber Polyester
fleece (50 g/m2) 3 240 16 36 1
Polyurethane - 2 ≥225 * ≥196 *
* Not calculated due to reaching maximum tensile testing course of machine - Test not performed
Extended abstract
8
0
50
100
150
200
250
Acrylic
Fibrous Acry
lic
Cementitious
Liquid silico
ne
Liquid rubber
Polyurethane
0%
40%
80%
120%
160%
200%
Maximum tensile force (N/50mm) Elongation at maximum tensile force (%)
Figure 3.3 – Tensile properties of 2- coat unreinforced LARWSs
Resistance to perforation in a given coating cannot be explained solely by its deformability or
stiffness, but should depend also on other intrinsic properties of each material. Although both
were highly deformable, there was a significant performance gap between the liquid silicone
and polyurethane based coatings when tested for resistance to perforation. Moreover, stiffness
cannot, in itself, account for a coating’s higher resistance to this type of mechanical damage.
Even though the fibrous acrylic coating was stiffer than all the other coatings tested, the results
showed it had significantly lower resistance to perforation than both the cementitious and
polyurethane based coatings.
Figure 3.4 shows the force-strain curves for one of the test specimens of each of the
unreinforced coatings, becoming clearer that the fibrous acrylic coating is the stiffest of all.
0
50
100
150
200
250
0% 50% 100% 150% 200%Elongation (%)
Forc
e (N
)
CementitiousAcrylicFibrous acrylicLiquid siliconeLiquid rubberPolyurethane
Figure 3.4 – Force-strain curves of the unreinforced coatings.
When reinforced, all coatings showed similar tensile properties to those of the corresponding
reinforcement layer (Table 2.2). An additional coat had no significant influence on the tensile
Flat roof waterproofing systems based on liquid products
9
properties of any of the reinforced coatings tested, but allowed for an 85% increase in the
maximum tensile force of unreinforced fibrous acrylic coating.
3.5. Flexibility at low temperature All unreinforced coatings except the unreinforced acrylic coating were submitted to a flexibility at
low temperature test. None of them showed signs of cracking and only the liquid rubber coating
became considerably stiffer.
3.6. User load category Table 3.4 shows the user load category of all the LARWSs tested, according to ETAG 005. For
all LARWSs, resistance to static indentation determined their user load category.
Table 3.4 – User load category of LARWSs tested
Resistance level Material Reinforcement
layer Number of coats Dynamic
indentation Static
indentation
User load category
- 2 I4 L3 P3 2 I4 L4 P4 Two-component
cementitious Fibreglass mat (4 mm mesh;
200 g/m2) 3 I4 L4 P4
- 2 I4 X X 2 I4 X X Acrylic Fibreglass mat
(2 mm mesh; 60 g/m2) 3 I4 X X
2 I4 L1 P1 Fibrous acrylic - 3 I4 L1 P1 Partially bonded two-
component cementitious
Unidentified fleece (90 g/m2) 2 I4 L4 P4
- 2 I3 X X 2 I3 L1 P1 Liquid silicone Polyester fleece
(50 g/m2) 3 I3 L1 P1 - 2 I4 X X
2 - - - Liquid rubber Polyester fleece (50 g/m2) 3 I4 X X
Polyurethane - 2 I4 L4 P4
X Coating did not reach minimum resistance level - Test not performed
The acrylic and liquid rubber based LARWSs tested should not be used on any kind of flat roof
due to their high susceptibility to perforation by punctual static loads.
Out of all the LARWSs tested, only cementitious (reinforced or unreinforced) and polyurethane
based LARWSs should be used on roofs designed for pedestrian traffic.
In addition to cementitious and polyurethane based LARWSs, fibrous acrylic LARWSs were the
only unreinforced systems suitable for use on flat roofs, but only of the non-accessible kind.
Liquid silicone based LARWSs should only be installed on flat roofs if reinforced and, even then,
only on non-accessible roofs.
Extended abstract
10
4. Conclusions
This study revealed significant mechanical performance differences between several available
LARWSs.
Cementitious, acrylic and polyurethane based coatings had a much higher resistance to
dynamic indentation than all the other coatings tested, including liquid silicone and liquid rubber
coatings. The results also showed a significant performance gap between coatings of different
materials after testing for resistance to static indentation. In this case, only cementitious and
polyurethane based coatings showed a resistance to punctual static loads that was clearly fit for
their intended use.
The use of a reinforcement layer yielded higher resistance to both dynamic and static
indentations, while an extra coat only led to a significant increase in the former.
The use of a reinforcement layer also changed LARWS tensile properties. The tensile
properties of reinforced coatings were similar to those of the corresponding reinforcement layer.
Tensile tests also showed that deformability and stiffness cannot, in themselves, account for the
significant performance differences between coatings of different materials.
In accordance with ETAG 005, the results of the dynamic and static indentation tests showed
that cementitious and polyurethane LARWSs are fit for use on flat roofs accessible to
pedestrian traffic. Due to their susceptibility to perforation by static punctual loads, the acrylic,
liquid silicone and liquid rubber LARWSs tested were, at best, fit for non-accessible roofs.
Further investigation is needed in order to determine the effect of ageing media, extreme
surface temperatures and substrate adhesion on resistance to perforation in each coating.
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Flat roof waterproofing systems based on liquid products
11
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