large wood wall

APPLICATION

Application and drying conditions

It is important to apply the paint under the right conditions.
We give you tips so you know how to go for the best result

spraypaint

Application and drying conditions

The correct film formation, curing, adhesion and absorption of timber coatings are all dependent on and heavily related to the conditions under which the coatings were applied and dried. The long-term performance and the aesthetic qualities of the coating system are therefore linked to the initial application and drying. Improperly cured coatings can be more susceptible to damage from moisture which can be particularly crucial on building sites where joinery items become wet as a result of exposure before installation and certain wet trades that are in progress.

Problems caused by incorrect drying can be as follows:
  • Bubbling of the topcoat in wet conditions
  • Milky looking areas in translucent and dark opaque finishes
  • Excessive water uptake through the coating system in wet conditions
  • Poor adhesion and absorption of the coating system

Low temperature can cause a range of problems such as the following:

  • Improper curing – the polymer used to bind the coating film together and hold the pigments in place coalesces to form a continuous protective layer. This process is assisted by the coating film being at a sufficiently high temperature. Also some constituents in the film cross link with each other and this cross linking process requires a certain temperature to take place. If the cross linking does not take place the coating does not build up the necessary protection against moisture
  • Cold joinery items can result in surface dew formation which will hinder absorption of the coating
  • Cold joinery items will lower the temperature of the applied coatings making them more viscous and less likely to adhere to and absorb into the substrate
  • Cold air temperature and storage conditions will make the coating more viscous resulting in reduced flow and lower absorption

High temperature can also result in problems:

  • Orange peel effect – before the coating film has had sufficient time to flow out to a smooth film the skin dries when the coating is still showing the undulations left by the spraying process. This leaves an orange peel effect in the surface
  • Mud cracking – this occurs when there is rapid skin formation over a liquid layer of paint. This can happen in very warm drying areas. The net result can be that the liquid or semi liquid layer is still moving and drying under the skin and cracks appear in the film
  • Dry spray effect – if the drying conditions are very warm and the humidity is too low one side of the joinery item has started to dry while the other side is still being sprayed. The wet spray layer lands on the dry layer opposite and forms a rough surface that does not flow out

High humidity during the drying process can result in problems:

  • High humidity in the surrounding air prevents moisture from escaping from the coating. This slows down the drying as the moisture has to escape from the wet film. High humidity can be a result of low temperature. The two are linked as warm air holds more water vapour so the relative humidity is lower

Low humidity during the application process can result in problems:

  • If the humidity is very low during the application process spray finishes will suffer from orange peel and potential mud cracking as described above because of rapid skin formation. A humidity of above 60% at the time of application allows the coatings to flow out better giving a much more attractive smooth finish
  • In the case of flow coating or dipping products higher humidity allows them to run off far more efficiently giving a better appearance

Recommendations

Ideal drying conditions are as follows as shown in this overview:

Once the drying process is taking place lowering humidity and increasing temperature will reduce drying times. Forced drying of temperature between 25 and 35°C and a relative humidity of down to 30% will promoted rapid drying. Air movement to remove local humidity is very important. An industrial fan as shown across will help with this and is highly recommended.


Assisted force drying can make very rapid drying and curing a possibility. An example of this is a catalytic IR (infra-red) drying equipment. When using this our Hydrolux exterior coating system can be dried at a rate of 20 minutes per coat. We have tested this with one of the leading manufacturers of this equipment. For more information click here.
drying time of paint
On windows and doors where the wood suffers from lower movement thick layer stains or varnishes can be used as they can cope with the smaller movement. Anker Stuy woodstains do not form a thick film layer as this will peel and flake on items where there is appreciable movement. Our woodstain products have a lower film thickness so they will not peel and flake as the wood moves and flexes.

spraypainting a table

General guidelines

  • Obtain a suitable temperature and humidity gauge to measure conditions in the factory. Data logging equipment is also available to monitor temperature and humidity fluctuations in the factory overnight and during the weekend to give a better idea of what the conditions are
  • Coatings can take 2-3 days to through dry or cure. We recommend you keep items above 15°C for period of 72 hours prior to exterior exposure of the joinery item
  • Store coatings at a suitable temperature. Never allow coatings to be stored under 5°C. Try to ensure they are at 15°- 20°C for application. Keep product on shelves or pallets and off concrete floors
  • Try to ensure the timber being coated is at a suitable temperature of 15°- 20°C
  • Try to ensure coating equipment such as spray pumps are at a suitable temperature 15°- 20°C