Sealing a Cypress Deck

House Doctor | Gary Dymski

August 17, 2000

Q. I recently replaced an existing deck. Pressure-treated wood was used for the load-bearing members, and cypress wood was used for the flooring and rails. It looks great, and I want the original look of the deck to last as long as possible. My builder says I should leave the wood, allowing it to weather naturally because it doesn't take sealant very well. Is there anything I can do to treat the deck and make it last? I have also noticed an increase in the earwig insect population since my deck was built. Is there a connection?

-R. Cardo, East Quogue

A. Cypress is easy to work with, resists decay and has a natural protective oil called cypressene that gives off an aromatic smell. In several parts of the country, this protective oil means no other protective treatment is needed. However, on Long Island, with the high humidity and insects, I would not build anything out of wood without applying a waterproof stain or sealant. Your contractor told you that cypress doesn't take stain. That's not quite true. Its grain pattern and surface are excellent for absorbing clear sealants, semi-transparent stains and even paints. If you do not apply some sort of protective coating, the wood will take on an antique gray appearance. It also will be subject to the sun's ultraviolet rays, mildew and even some splintering.

Because you want the cypress deck to look new, I would suggest a neutral semi-transparent stain or a clear deck and siding finish. Cypress is compatible with linseed oil-based stains that have water-repelling properties and UV inhibitors. Several companies make such stains or sealants, including Cuprinol, Olympic and Behr.

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Remember, though, once you add a stain or clear sealant, you'll have to treat the wood every couple of years or so. Most manufacturers have specific guidelines for refinishing, so be sure to follow the instructions on the can. In your case, a stain or sealant is probably a good idea for the entire deck, because your frame is made of pressure-treated wood, which should be treated regularly for maximum protection.

One advantage to using cypress for the floor and rails of your deck is that the wood contains no arsenic salts, which combat decay and insects in pressure-treated wood. In cypress, the natural ingredient cypressene fights insects and decay. As pressure-treated lumber dries, arsenic salts can come in contact with your skin, sometimes causing sensitive reactions, especially in children.

As for the earwigs, I doubt they have anything to do with the construction of your new deck or the cypress deck lumber. I suspect you have another problem, such as organic debris in shady places. Clean out all shady areas that have old leaves, grass clippings, weeds, clods of dirt or even ivy.

You can make earwig traps from old tuna cans and vegetable oil. Fill the cans with about a half-inch of oil and place them in the area infested with earwigs. As the earwigs enter the cans, they'll slip and fall into the oil and drown. When the cans fill with earwigs, dispose of the insects and refill with oil.