Staining from timber is a brownish or tan discolouration of waterborne house paint or stain that can occur when the paint or stain is applied over bare wood. Naturally it can be quite unsightly on white or light-coloured paints. Although the discolouration may bleach out in open, exposed areas, it can be very persistent in damp areas that receive little sunlight. Staining commonly occurs when water soluble tannins found in wood, particularly cedar, redwood, kwila and beech, seep through waterborne paint or stain and discolour it.
The condition can also occur over painted knots of other wood species including some types of pine, and it can sometimes be observed where previously painted pine has peeled down to the bare wood, permitting the staining material to rise to the surface.
To avoid staining, bare wood should be primed with Resene Wood Primer. This primer will keep the wood tannins from bleeding into the topcoat, except in the most severe cases.
Note that for cedar, a pre-treatment with Resene TimberLock is strongly recommended. This is to help bind up and strengthen the timber surface of the very soft cedar.
Stains usually appear immediately but may appear after rain. A barrier coat of enamel paint or using solventborne stains is the only way to fix these problems.
Imported hardwoods may also stain and decking timber left unpainted can cause stain splashes onto surrounding painted weatherboards or staining to other surfaces.
Always test the finish you plan to use with a Resene testpot. If you see tannin staining occurring then ensure you seal the surface with an enamel primer or use a solventborne stain system.
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