pallets and packagingbest practice guide to timber stain and mould

for users of wooden palletsMouldMicroscopic mould spores are everywhere in the airconstantly floating around settling on any surface(not just wood). Optimal conditions are - moisture,warmth, oxygen, food source and lack of ventilation.Mould spores will germinate in favourableconditions and grow producing more spores forreproduction.

Conditions that favour the development of mouldare the same for blue stain – surface moisture inexcess of 20%, moderate to warm temperature (15- 32 C) and poor ventilation.

Kiln dried or air dried timber at ≤ 20% moisturecontent produces unfavourable conditions formould germination and blue stain fungi to develop.Pallets delivered dry are susceptible to mould andstain if they become rewetted by rain or exposureto other sources of moisture. It is importanttherefore to store wooden pallets in dry and wellventilated environments and to ensure as far asreasonably practical, minimal exposure to moistureup to final delivery of palletised goods.

Visually it can be difficult to tell mould from stain.Mould spores grow on the surface of the timberwhereas stain is a discolouration of the timber. Asimple rub test using a cloth or disposable wipeover the affected surface will generally give apositive result. Mould spores will rub off onto thewipe whereas stain will not. Wipes used for thispurpose must be properly disposed of and not beallowed to come into contact with any other surfaceto prevent transfer of mould spores.

TIMCON has produced this guide forusers of wood packaging (pallets) togive an insight into timber stain (bluestain) and mould.

What differentiates mould from stain andhow to determine the difference? Whiletimber stain is important to the user fromthe perspective of aesthetics of unit loadappearance, mould carries the stigma ofuncleanliness and risk to human health.

The main purpose of this guide is to focuson practical measures outlined herein tominimise the risk of mould occurring.

Timber StainTimber staining (blue stain or sap stain) typically bluishor greyish can also be black discolouration of woodcaused by deeply penetrating fungi. The discolourationis permanent and may appear unsightly but its effectsare cosmetic and pose no risk to human health.

Testing in Europe and North America has confirmedthat blue stain has no detrimental effect on thestrength of the wood. The European Standards BodyCEN confirmed this in BS EN 2246 1999, Qualityclassification of timber used in pallets and packaging,where it permits the unrestricted use of blue stainedtimber.

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“dry” term relates to average moisture content of a dried wooden pallet that forms a contractualagreement between supplier and customer

TransportationVehicle trailers (curtain or box) must be checkedbefore loading palletised goods to ensure they areclean, free of pooled water, wooden flooring is notdamp and there are no leaks. Conditions inside closedtrailers are affected by climate changes. Condensation,darkness and lack of ventilation, are all factors to beconsidered particularly involving extended time spentin the trailer and long haul journeys.

Steel shipping containers present different challengeswhen exposed to extreme internal and externalclimate changes during shipment across differenthemispheres. Condensation on walls and ceilingsinside the contained will drip water (container rain)onto both the product and pallets. High levels ofhumidity and temperature inside the container bathedin darkness and no ventilation are favourableconditions for mould growth.

Maintaining the dry condition of the pallets before andduring loading of the container is important. The use ofdesiccants will help to absorb moisture inside thecontainer. Choosing a container lined with plywoodwill also help to minimise the risk from moisture.

DisclaimerThe information in this publication has been produced in good faith forgeneral informational purposes only, and is subject to change withoutnotice. Nothing contained in any part of this document constitutes legal,investment, tax or other advice, nor should it be relied upon in making aninvestment or other decision or for any other specific purpose and noundertaking, representation or warranty (express or implied) is given asto its accuracy, reliability or completeness.We have made reasonable efforts to ensure that all information in thisdocument is accurate at the time of inclusion, however, there may beerrors in such information for which we apologise, but shall have noliability. We cannot guarantee that any information displayed here hasnot been changed or modified through malicious attacks or “hacking”.We may have included certain material in this document which has beenproduced, provided or written by third parties. Such material is providedfor information purposes only and should not be taken to represent theopinions, beliefs or views of TIMCON or any of its directors, members,officers or employees.

User ResponsibilityIt is important to note that no wooden pallet can beguaranteed mould free when mould spores, anatural phenomenon, are forever present in the air.Wooden pallets supplied with dried timber to arequired moisture content, will ensure the pallets aredelivered free of visible signs of mould and potentialrelated problems for the user.

The pallet user must acknowledge they also have aresponsibility to prevent mould.

By following the requirements stated to keep thepallets dry, remains the best practice strategy toprevent mould growth.

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Unit Load PackagingThere are disadvantages associated with the use ofplastic wrap and shrink wrap as described further on.Users of this type of tertiary packaging must considerthe potential effects and take appropriate action toensure both goods and pallet are ventilated.

Plastic wrapping product to a pallet particularly whenthe product is warm will cause condensation to formon the inside surface of the wrapping. Thiscondensation is trapped and will be absorbed backinto the pallet. The warmth and trapped moisture arefavourable conditions to cause mould.

Similar effect of condensation and moistureabsorption will occur when product and pallet areencapsulated in plastic wrap and stored in direct andwarm sunlight.

Plastic wrapping extending over the pallet perimeterand blocks encapsulates the pallet restricting air flow.The natural and continuous process of timber dryingcreates condensation between the timber blocks (alsocomposite blocks) and plastic wrapping. Trappedmoisture, no ventilation and relative warmth betweenpallet blocks and plastic provide favourable conditionsfor mould.

Goods stacked inbound of the pallet load deckperimeter with the wrapping extended over theperimeter of the deck, creating a tent effect.Consideration should be given to the use of a slipsheet or protective membrane between the packagedgoods and surface of the load deck. This will preventany trapped moisture being absorbed by the pallet.

Use of perforated plastic wrapping improvesventilation providing the wrap is evenly distributedover the load enabling the perforation to work asintended. Overwrapping the perforation as is often thecase being counter-productive to intended purpose.

Palletised goods should be regularly checked instorage for any signs of mould occurring.

Outbreaks of mould contamination must be dealtwith quickly to reduce airborne spore density. Smallpatches of mould can be removed by spot cleaningusing a 2:1 ratio of water to household bleach.

The bleach kills existing mould and prevents furtherrelease of mould spores but it does not preventmould from reoccurring. Vigilance and a goodhousekeeping regime will minimize the potential formould growth.

Pallets should not be left in closed trailers longerthan 24 hours before unloading.

Pallets transported in curtain sided trailers thatcannot be immediately unloaded, opening thecurtains will improve ventilation in dry weatherconditions.

Storage under canopy (Dutch barn), pallets mustbe stored sufficiently inbound of the roof perimeterto afford protection from precipitation, spray andwater splash from passing vehicles. Avoid this typeof storage environment which is open to prevailingwind from open fields or farmland blowing moistureladen air onto stored pallets.

Wherever it is practical to do so, avoid blockstacking pallets in close (touch) formation, thisrestricts airflow between the stacks and inhibits thenatural drying of moisture from the wood.

Avoid pallet storage in dark or dimly lit areas andwarm temperatures without ventilation.

Pallets that have become surface wet or frozen inwinter should be allowed to dry (thaw and dry) in awell-ventilated environment before being broughtinto heated environments.

Stacks of pallets should be arranged in storagewith a minimum perimeter gap of 100 mm forventilation around each stack. Storage spacepermitting, air flow across stacks of pallets isimproved when pallets are stacked in neat rows inthe X axis, orientating the rows in the Y axis(offsetting alignment) improves airflow across thestacks.

Stacks must be kept away from direct contactwith building walls and steel cladding. This willprevent any damp, moisture condensation ormould spore transfer to the pallets. Dry controlledpallets should not be stored adjacent to or in thesame area as uncontrolled pallets stocks toprevent any risk of cross contamination.

Operate FIFO, ‘first in first out stock rotation’.Pallets continually blocked in escape notice ofany change in condition often until it is realizedthere is a mould problem.

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Unloading and StoragePallets must be unloaded from the vehicle trailer upondelivery and stored protected from rain in a well-lit andwell-ventilated area with good drainage to eliminatestanding water, away from other sources of moisturefor example, vented from machinery or processingactivities.

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