Previously stained wood

Inspection of surface

1. The condition of the substrate needs to be established.
2. Use a water-drop test to see how quickly or slowly the water disappears. If the surface is quite well sealed the water remains on the surface indicating that the woodstain is still protecting the wood. If the water sinks in the wood is unprotected by the stain and needs re-coating firstly with an appropriate basecoat to penetrate the surface and provide a key for subsequent coats of Woodstain.
3. The amount of chalking and degradation of the film when it is rubbed is another good indication of what sort of preparation must be given to the timber. If it is badly degraded it has to be washed and thoroughly rubbed down before being basecoated.
4. Identify the condition of existing stain by the continuity of the film and of the timber surface. If the surface is split and cracked all over it is pretty certain that loss of protection has occurred.

Surface Preparation

Correct preparation will ensure better performance of the surface coating and particular care should be taken when preparing previously coated (painted or stained) surfaces before applying a new protective coating. It is recommended that the following guidelines be observed:

1. Existing coatings need not be removed before re-coating provided they are in sound condition (firmly adhering and not significantly cracked or blistered) and a similar material is to be applied. All Dulux and Weathershield paints, varnishes and woodstains are free from any added lead. However the wood and metal surfaces of the building especially if it is pre-1960 may have been decorated in the past with a paint made with lead pigments. Preparation and removal of such paint can be hazardous. There is a free leaflet explaining how the surface should be prepared safely available on request from the Dulux Technical Group at Slough or the BCF (British Coatings Federation). If a woodstain is to be applied to a surface previously painted or varnished then previous coatings must be completely removed in accordance with the advice on safe working practice given in the leaflet referred to above.
2. Burning off with a blowtorch (naked flame) is one method of removing paint from woodwork which is to be repainted. But it is almost inevitable that the wood will be scorched in places so this method is not suitable if woodstain or varnish is to be applied. Also there is an increased fire risk which should be taken into account.
3. Chemical paint removers provide an alternative method of stripping. Hot-air strippers are another - delivering a stream of air at around 500ºC which is sufficient to soften paint and varnish coatings without scorching the wood.
4. Chemical paint removers based on caustic soda, potash and similar materials should not be used as their residues are difficult to remove and will cause durability failures particularly when used on exterior wood. Some woods are markedly discoloured by alkali materials. Solvent-based solvent-soluble paint removers are preferred for wood. It is important that the wood is allowed time to dry out afterwards.
5. When several dwellings are to be treated, abrasive blasting is economical and leaves wood in good condition for staining. But a test area should be treated first to ensure that the fabric of the building will not be damaged.
6. Powdering or chalking of coatings is usually confined to the immediate surface layer and (except where changing from paint to a woodstain) the removal of the whole coating may not be necessary. Thorough rubbing down preferably wet generally provides a satisfactory base for recoating.