Cypress decking or siding should be finished promptly at the time of installation to protect against moisture absorption, discoloration from rain, and mildew. However, under no circumstances should decking or siding be finished when the wood is wet. Before finishing (or refinishing), repair all nail holes and surface irregularities. All surfaces should be clean and any caulking should be in good condition.
A high-quality water-repellent sealer should be applied to all sides and ends as soon as practically possible (do not apply if the wood is wet). For siding applications, allow the water-repellent sealer to be absorbed and dry to the touch so the solvent will not react with foam sheathing. Clear coating must be reapplied at frequent intervals to maintain protection.
As with any wood, sealer should be reapplied to cypress decking and siding every one to two years. For best results, an exterior wood cleaner should be used to remove dirt and mildew before any sealer is reapplied.
The best sealing products are those that actually penetrate the wood. Most also contain a moisture inhibitor such as paraffin wax and a binder. Some also contain a pigment to add color.
When purchasing a sealer, be sure to distinguish between “paintable” sealers, which contain lower concentrations of water-repellent (to facilitate the application of paint) and stand-alone sealers, which contain a high percentage of water-repellent. Consider using a water-repellent preservative, which usually contains a mildewcide along with a moisture inhibitor.
Decking: If you want to stain your deck, penetrating transparent or semi-transparent oil-based products formulated especially for decks usually work best. You can use more than one coat as long as subsequent coats are applied while the previous coat is still wet (usually within 30 to 45 minutes). If the stain has already dried, subsequent coats create a film that will eventually produce unsightly cracks in the finish.
Do not use a stain formulated for siding or other such surfaces. Paint or heavily pigmented stains (solid color stains) also are not recommended for cypress decks.
Siding: Cypress takes stains very well, however, semi-transparent stains do not last as long as paint systems. Most semi-transparent stains provide adequate protection for 18 to 24 months, depending on weather conditions. Consequently, they require reapplication at regular intervals to protect the wood siding from warping, checking, shrinking, and loosening of nails.
Selecting Primer and Paint: Use a high-quality primer compatible with the paint being used—most paints will require an oil-based alkyd primer. High-quality, 100-percent resin acrylic/latex paints are recommended. Certain paints contain water-sensitive polymers and/or surfactants that might absorb moisture, causing the siding to swell or creating an environment suitable for biological degradation. These additives are present in a variety of paints, at different price levels, and their presence is not necessarily reflected on the label. The only safe approach is to use paint specifically recommended by a paint manufacturer for use on exterior wood siding. Light-colored finishes reflect heat more than dark colors and reduce the possibility of shrinking, checking, warping, and loosening of nails.
Applying Paint: Always follow the primer and paint manufacturer’s recommendations. Priming all sides and edges of wood siding provides superior performance over all types of sheathing. After the prime coat has dried, apply two coats of high-quality paint to all exposed surfaces and edges. Brush application is recommended because it provides more uniform coverage. Time of day, temperature, dew, fog and rain influence the quality of the paint job (consult the manufacturer’s recommendations).