Good Practice guidelines for the Manufacture and Finishing of joinery products under controlled factory conditions during 
cold/damp periods.
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Please find below a reminder of some of the basic conditions, under which, the water borne products and system will be allowed to perform at their optimum levels, and an explaination of the key factors involved in this topic.
1. Coating Systems.
The optimum performance of single pack Acrylic paint systems is dependent upon an ambient temperature of between 15° and 25° C, these requirements refer to the temperature of all factors involved, including:-
The paint: Applying 'cold’ paint will lead to restricted flow properties, poor application characteristics requiring additional thinning, and a poor surface appearance. Also, the drying process, will require more time, and additional heating will be required in order to raise the temperature of the applied film to that at which it will dry correctly.
The wooden substrate: Application of a coating system to a ‘cold’ surface will naturally cool the paint, even if the paint itself is at the correct temperature. This will potentially lead to the same problems detailed above, but can also be worsened by the formation of a condensation layer at the timber surface, leading to potential poor adhesion issues.
The spray room: In order to maintain the above temperatures for both paint and timber, the ambient conditions in the application area should be at a level which will allow this. i.e. if paint and timber have been correctly stored say at 20C, is applied in a spraying area of only 10C, it will soon lose heat and acclimatise to it's surroundings.
Lower temperatures relating to the paint, surface and environment, particularly during the full drying process, will reduce the film forming properties of the coating, which in-turn increases the water vapour uptake potential of the coating system.
Drying times usually lie between 4-6 hours, depending on the paint system, the individual layer thickness & drying conditions. As with using timbers with high extractive contents, cold and damp conditions cause paint systems to take longer to dry, or even not completely dry.
Dry film builds significantly higher than our optimal 150µm, firstly take longer to dry and secondly make the paint film less permeable and can be the cause of coating de-lamination in the presence of high moisture contents.
When higher film builds are applied, additional drying considerations will be necessary.
A wet film of 150µm will dry in approx. 4-6 hours in standard ambient conditions (23° C, 50% RH).
A wet film of 300µm will take up to 16 hours in the same conditions.
Failing to ensure correctly dried layers within coating systems will increase the through drying time of the complete system considerably.
If the coating does not cure correctly in the factory, it may not cure on site, even when the temperature increases.
2. Glue and Adhesives.
The temperature of the material, substrate and ambient conditions are, as stated above, critical to the optimum performance of the adhesive system chosen.
Single component adhesives (PVA) require a working temperature of at least 15° C for both glue and substrate. Lower temperatures or higher timber moistures (>15%) will increase the pressing / drying times and may reduce the bond efficiency.
The pressing times of PVA glues vary between 6 – 40 minutes depending on which type of adhesive is being used and whether Softwood or Hardwood. Pressing sequences should be checked by the adhesive manufacturer for correct bondage (>7 N/mm²).
Alternatively, consider a two component adhesive which has chemically curing properties but always seek the manufacturers advice.
An EN D4, Watt 91 rated adhesive is recommended.
If glue does not cure correctly in the factory due to low temperature, it may not cure on site, even when the temperature increases.
3. Moisture content of timber.
Joinery moisture content (mc) should be delivered corresponding to it's intended end use situation. For most exterior joinery situations, a moisture content of between 12-16% is acceptable, with 14% being a good average figure. Significant deviations to this may cause dimensional changes in the joinery as it reaches equilibrium with its surroundings.
Swelling and shrinking of a joinery item is often sufficient to break open joints, allowing free moisture passage into the joint and worsening any movement potential present.
The change in surroundings from factory to installation, becomes critical when Joinery is installed into buildings which have not been adequately dried out. Significant amounts of moisture at high vapour pressure levels, can be absorbed by the joinery during the drying out phase of new build projects, resulting in mc’s being much higher than would be considered normal once the drying out phase is completed.
These high mc’s lead to excessive movement resulting in the opening of joints, moisture ingress, timber discolouration and coating failure.
In the damper /colder months, extra time (minimum 72 hours) should be considered between fully finishing and delivery to the construction site. The joinery should be kept in an area which has warmer conditions prior to delivery:- 20° C if possible, and should also be well ventilated before wrapping with polythene sheeting.
Once wrapped, the joinery cannot ventilate.
When installations are completed during cold and damp periods it is advised to heat and ventilate the building simultaneously.
Cold, damp buildings increase the risk of the timber swelling, or even de-lamination of the coating system due to increased water vapour transfer passing through the paint system.
Periodically airing the room through cross flow ventilation is important.
Ventilation during the drying of plastering, screeding, painting and tiling is particularly recommended.
4. Storage.
Windows should be stored under cover even if fully finished, preferably inside a heated and ventilated building. If they have to be stored outside they must be kept clear of the ground on level bearers and also protected from direct sources of moisture and sunlight.
Polyethylene sheeting wrapping should not be used as this can act like a greenhouse and encourage damp or humid conditions. There must be space for air circulation around and between the windows.
When stored inside a building, windows should be protected from dirt damage and building trades.
Windows should be checked at the time of delivery to ensure that they are in accordance with the order schedule; that the delivery is complete and that each window, including any protective packaging, is not damaged.
All products must be fully checked for damages before installation or storage and any defects to the joinery must be reported immediately.
Whenever possible the sequence of deliveries should be co-ordinated to the site requirements so that windows are not kept on site unfixed for longer than necessary. The storage place should be prepared in advance and the windows unloaded straight into it.
5. Protective tapes.
The use of low tack tapes suitable for waterborne paints (seek manufacturers advice) is recommended. Higher tack or ‘all purpose’ tapes may cause damage to the coating. Tapes should normally be removed within a maximum of two weeks (seek manufacturers advice).
6. Cleaning.
Clean only with neutral cleaners.
A mild household detergent solution in hand warm water is recommended.
Avoid cleaning finished joinery with solvents or brick cleaner as the strong chemicals may damage the paint finish. Avoid harsh abrasive cleaners.
We hope that you findthis information useful. Please do not hesitate to contact us for further clarification.
Information provided courtesey of Akzo Nobel.
Errors and omissions excepted.