- Can we obtain a clear coating system for timber and if so how long does it last?
Clear coatings for timber tend to show very poor long term durability. This is because the timber is hit by UV light which damages the surface of the timber. This destabilises the surface and leads to loss of adhesion of the coating. UV light also tends to damage the resin film of the coating on the timber making it become brittle. If pigments are introduced into transparent coatings the pigments are able to absorb and reflect the UV light and reduce or slow down the damage to the timber and coating. The more pigmented the coating the more absorbency or reflection of the UV light takes place. It is possible to place large amounts of clear UV light absorbers into a coating but these make the coating extremely expensive to manufacture and still only give life spans of between 2 and 4 years in most cases.
- Can we obtain a paint finish that will resist knot staining on softwood?
It is possible when using the right type of primer such as PPG Wood Finishes PE25RO to minimise and slow down the onset of knot staining. In extreme circumstances when the coating becomes very warm or there is a lot of resin present in the knot then knot staining will occur even when the right primer is used. While there is no guarantee against knot staining PPG Wood Finishes PE25RO has been proven to be very effective against it in most cases.
- Why do I still experience timber movement even though I have put a full coating system on my joinery?
Timber movement is usually caused by a large change in the moisture content of the timber or the use of a timber that is unstable to moisture related movement. Joinery being coated too dry and then being put in UK wet weather is often a cause of movement, try to coat joinery between 13 and 16% moisture content if possible. Joinery being placed in a very wet environment with no ventilation is another common reason for excessive movement, try to avoid leaving windows and door closed on new build sites where there is wet plaster, or concrete as the moisture from the drying material has no place to go apart from into the timber. Finally ensure the timber coating is properly cured before sending joinery out on site. For PPG Wood Finishes PE152QO, 48 hours is enough time to dry the coating sufficiently to protect the timber from excessive water uptake through the non cured coating. Acrylic primers can take as long as 7-10 days before they can be placed in wet weather conditions otherwise severe moisture uptake can be the result.
- Why is my translucent finish going milky in appearance when it rains?
Water-borne top coats often contain a small amount of solvent to help them form smooth films when drying. If the coating is not sufficiently dried or an appreciable skin forms before the coating underneath has had time to dry the solvent remains in the finish. This solvent goes milky when water gets onto the surface of the film. Try to ensure coatings are dried properly in the factory before putting them out in the rain. In most cases the solvent will dry out of the coating film and the effect will start to dissipate and eventually not reoccur.
- Why when I coat certain hardwoods do I get a pink or yellow discolouration of white paint finishes?
Many hardwoods contain water soluble tannins (or extractives) which can discolour paint finishes. It is important to isolate these tannins within the coating by using the correct primer. PPG Wood Finishes PE152QO and PE025RO are highly effective at isolating tannins reducing the possibility of tannin staining.
- Why am I getting bubbles appearing in my dry paint or stain finish?
Coarse grain timbers often have pores in the surface and when the paint does not fill these pores air from them escapes through the drying film causing bubbles to appear. Try using pore filling primers and mid coats such as PPG Wood Finishes FE164QO and PE152QO. These flow into the pores removing air before the paint film dries.
- Why is my coating taking so long to dry, especially in winter?
Modern water borne coatings rely on driving moisture out of the drying film. In warm conditions relative humidity is often quite low and water can freely escape from the surface of the drying coating. Even in warm conditions relative humidity will rise if there is poor air movement so it is essential that warm air is also combined with good air movement if the coating is to dry successfully. Try using heaters to warm up drying areas but not paraffin heaters or other devices that produce moisture as they work. Ensure air is moving around the drying area and that wet air can find a way to escape from the drying area. Conservatory type fans are often very effective as they create air movement but also drive warm air (that has a tendency to rise to the ceiling) back down to floor level.
- Why are my translucent colours so patchy?
Timber tends to exhibit uneven absorption across the surface, it therefore absorbs more of the coating and gives greater pigmentation on certain areas of the timber. There are various ways to combat this:
- Try to ensure the timber is abraded evenly across the surface. If certain areas have been abraded more severely due to sanding over filler for example, these will absorb more stain.
- Use base stains with more opaque pigments. These will tend to colour the surface evenly if there is slightly variable absorption.
- Use top coats that are more opaque. These will hide areas of different absorption.
- Use a clear coat on the timber first. This can take up the absorption of the timber which reduces the over absorption of the translucent pigmented coats that follow.