Water-repellent (WR) preservatives of some types are formulated with non-drying oils. These oils penetrate the wood to protect it against degradation. The deck surface may remain oily until the finish absorbs, which may take several days.
Advantages of Water-Repellent Preservatives
- Retard decay in above-ground applications
- Decrease raised grain, checking, warping, and splitting
- Inhibit mildew growth on both painted and unpainted wood
- Retard iron stain
- Stop extractive bleed
- Improve paint adhesion
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A Water Repellent Preservative (WRP) is an effective finish for a fully exposed deck. Although the deck will need to be refinished frequently, there is no need for laborious surface preparation, as is required by film-forming finishes. Annual refinishing can be done quickly using a brush, roller, or pad. Brush application works the finish into the wood better than do the other methods. The finish should be applied liberally to decay-prone areas around fasteners and end-grain.
Pretreatments for Painted Wood
New Wood--Water repellent and WRP formulations for use as pretreatments for paint have less wax or other water repellents compared with those formulated for use without paint. When used as a pretreatment before painting, a WRP can be applied in the same way as when used as a natural finish. Freshly treated wood must be allowed to dry. If the treatment is applied with a brush, allow 2 days of drying in warm weather before painting. If the wood is dipped for 10 or more seconds, 1 week of drying is necessary before painting. If enough time is not allowed for most of the solvent to dry from the wood and for the wax to absorb, the paint applied over the treated wood may not cure or bond properly. Open joints, such as in siding, miliwork, and facia, should be caulked after treating with a WR or WRP but before priming.
Refinishing--When applying a WR or WRP to previously painted wood, loose paint must be removed; the WR or WRP should be brushed into the joints and unpainted areas. Remove excess WRP from the painted surfaces with a rag. Allow 3 days of drying in warm weather before repainting.
Removal of Mold and Mildew
If mildew is present, pretreat the wood with a commercial cleaner or a chlorine bleach-water solution. Allow the wood to dry for 1 or 2 days before refinishing.
Removal of Mildew
Commercially available wood cleaners work quite effectively to remove mildew and other stains on wood. A mildew cleaner can also be made by dissolving 1 part liquid bleach and some powdered detergent in 2 to 4 parts water.
Suggested formula:
1/3 cup household detergent
1 quart (5%) sodium hypochlorite (household bleach)
3 quarts warm water
[Note: 1 cup =0.2 liter; 1 quart =0.9 liter]
CAUTION: Do not use a detergent that contains ammonia; ammonia reacts with bleach to form a poisonous gas. Many liquid detergents may contain other additives that react with chlorine- containing bleach.
Service Life
The service life of WRs and WRPs is about 1 year on exposed wood surfaces. However, WRPs are extremely easy to reapply to some structures, such as decks. Water repellents and WRPs absorb readily into the end-grain of lumber and can stop water absorption for many years.
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