SURFACE PREPARATION
| The surface condition of the wood to which the finish is to be applied can substantially affect the performance and hence the life expectancy of the finish. The following procedures should prove helpful:
New Wood
New wood such as cedar siding and trim, should be protected from the weather before, during and after construction. It is seldom necessary to carry out extensive surface preparation providing the wood has not weathered for more than two weeks and is clean and dry. If it has been contaminated by dirt, oil and other foreign substances they must be removed.
For smooth-planed, flat-grained cedar, some surface preparation may be desirable. On flat-grained wood, the surface should be scuff-sanded with 50-60 grit sandpaper. This procedure will |
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| Here, the image of naturally aging cedar is counterpointed with solid-stained splash areas and densely whitened window and trim boards |
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greatly increase the coatings performance but will not detract from a smooth finish. Surface preparation is not necessary for textured cedar.
Weathered New Wood
Weathered new wood that has been exposed to the elements for longer than 2 weeks may have a degraded surface that is unsuitable for painting. Preparing the surface by sanding, brushing, and washing before applying the finish is recommended.
Paint Finishes
Paint finishes must be removed if the old surface is severely peeled, blistered, or if cross-grain checking has occurred because of excessive paint build-up. The removal of a film-forming finish is also necessary if a penetrating stain or water-repellent finish is to be applied to a previously painted or solid-color stained surface. Note that changing from a film-forming to a penetrating finish sometimes does not give satisfactory results because residual paint inhibits absorption.
Finishes can be removed by sanding, wet sandblasting, pressurized water spray, electrically heated paint removers and chemicals. Although quick and easy, sandblasting and pressurized water spray are not recommended unless extreme care is taken to avoid damage to the wood's surface. Special precautions to ensure worker safety must be taken if the old paint is lead-based. |
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| The unifying effect of a solid-color stain is used to good effect on this residential housing complex. |
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Weathered Water-Repellent Preservative Finishes
Weathered water-repellent preservative finishes should be cleaned with a non-ferrous bristle brush to remove loose fibers and dirt. If the surface is soiled, it may be scrubbed with a mild detergent solution. If mildew is present, it should be controlled. The surface should be thoroughly rinsed and allowed to dry completely before refinishing. Caution: Never mix bleach with detergent containing ammonia as the fumes can be harmful or fatal. Weathered Penetrating Stains
Weathered penetrating stains on mildew-free surfaces are relatively easy to refinish. Excessive scraping or sanding is not required. A stiff, non-ferrous bristle brush may be used to remove surface dirt, dust and loose wood fibers before applying the stain. |
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