Identify the timber, its moisture condition and the type of staining.
All decorating problems
Moisture & stains · H&C advice
Wood knots & tannin staining
Natural wood constituents can discolour a painted finish.
- Brown patches around knots or timber grain.
- Discolouration returning through light-coloured paint.
Understand before treating
What might cause it?
Similar-looking defects can have different causes. Assessment comes before product choice.
Resinous knots and tannins in certain timbers may bleed into a coating. Moisture and the finish used can affect the result.
Preparation & next steps
How we approach it
Clean and prepare sound timber, treating knots where the chosen system requires it.
Select a primer specified for the timber and stain, followed by a compatible interior or exterior finish.
Rotten or persistently wet timber needs repair and the moisture source addressed. Check exterior suitability rather than relying on a general stain blocker. Check current product technical data, safety instructions and compatibility; this guide is not a site diagnosis or a guaranteed repair specification.
The right system for the surface
Product selection matters
A suitable primer or sealer may be part of the preparation, but it cannot replace fixing the cause. Zinsser is one of the brands we use; the exact product depends on the surface, defect and intended finish.
Zinsser UK product guidanceOriginal H&C guidance. We are not approved, accredited or endorsed by Zinsser.
Local decorating help
Let’s look at the problem properly.
Share your postcode, the affected surface and what you’ve noticed. Preparation and repairs are assessed before a quote is agreed.