Sealing a Pressure Treated Deck

Should You Seal a Pressure Treated Deck

By Mark J. Donovan

Question: Hi Mark, I have had some deck work done to our camp in Maine recently and have a question about whether or not it is necessary to seal a pressure treated deck. The deck contractor who did the work says you don’t need to put a sealer on a pressure treated deck. I’ve always been under the opinion that after the deck has had some time to dry out that I need to apply a deck sealer. I am interested on your thoughts on whether or not it is wise to seal a pressure treated deck.

Answer: O.V. To answer your question succinctly I am of the same opinion as you, and so are the treated lumber manufacturers. I think your deck contractor either does not know what he is talking about, or more likely he doesn’t want to be bothered in coming back to your deck project to seal it.

If the pressure treated deck is left unsealed inevitably, like any other type of wooden deck, Mother Nature will have its way with it. The wood will begin to check and split and water will slowly begin to work its way into it and begin the decaying process. In addition, mold and mildew growth will begin to occur as the moisture soaks into the cracks.

If you plan on applying a clear deck sealer to a pressure treated deck it is best to wait at least a couple of months to allow the pressure treated lumber to dry out. You can test to see if the deck is ready for a sealer by spilling a little water on it. If the water runs off of it or beads up then it is not yet ready to seal. If the water absorbs into it then it is ready for a sealer. A roller and brush work great for applying a clear deck sealer. Just make sure to not apply too much and that the weather forecast is dry for 24 to 48 hours.

Otherwise you’ll end up with a sticky deck that takes many months to fully dry out. In addition, the deck may begin to peel if you apply too much deck sealer.

 Sand your deck and restore it to looking like new!

I personally like using a semi-transparent stain on my pressure treated decks. This way you add a little color to the wood while still allowing the texture and beauty of the wood to shine through. In addition, there is no peeling to worry about. Years ago I use to apply clear water sealers to my decks and inevitably they would peel. To remove the old sealer I had no choice but to sand down the entire deck.

Suffice it to say you don’t want to end up having to sand a deck. It’s a lot of hard, noisy work. Since using a semi-transparent stain I’ve never had to sand a deck again prior to applying a fresh coat of stain.

Typically I apply only one coat of sealer or semi-transparent stain to the deck every year or two to keep the deck looking good and to provide the best protection to the deck.

Make sure before applying a deck sealer or stain to clean the deck thoroughly. A pressure washer works great for cleaning a deck, but be careful to not damage the wood in the process. Pressure washers can damage the wood grain and leave permanent scars in the wood.

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