— Gina H., Cilleyville, N.H.
A: A lot of people suffer this agony each spring. I'm hearing more and more complaints about deck sealing products that peel and flake.
Let's talk about wood stains for a moment. If you've ever stained interior wood, you might have used a colored liquid that's the consistency of water. These stains typically soak immediately into the wood fibers, and nothing is really left on the surface of the wood but some microscopic pigment particles.
Years ago, many outdoor wood stains and sealers were made the same way. They penetrated the wood. That said, there were outdoor sealers you could buy that behaved more like urethanes or varnishes. These are film-forming products that deposit a resin or coating on top of the wood. When they fail, and they all do, they peel and flake. It seems many of today's deck sealers are film-formers.
The failure of the outdoor deck sealers is predictable. The sun's harsh ultraviolet rays blast apart the film-forming sealers with little effort. Also, wood swells and shrinks as it absorbs and releases water.
I just started testing a penetrating wood sealer stain a month ago. I used it to seal my boat dock panels and the stairs leading down to the dock. I have a combination of treated lumber and cedar. I could tell it penetrated the wood fibers, and if it left a resin on the surface, it's very light. The product description says it's a penetrating sealer.
The only thing I didn't like about it is that it's a combination of three oils: linseed, tung and long-oil alkyds. These are scrumptious food for mold and mildew. I'm sure the manufacturer added chemical additives to prevent the growth of these things. After one month, I've not seen any trace of mold or mildew growth. Water beads up wonderfully on the wood surfaces, so it's doing a good job of protecting the wood.
You get the best protection from a sealer that has lots of dark pigment. The pigment acts like sunscreen. It sacrifices itself to the UV rays and slows the destruction of the wood fibers. You can see the UV damage caused by the sun after cleaning the wood. Have you seen the peach fuzz after the wood dries? Those are sun-damaged wood fibers just hanging on.
To clean my outdoor wood, I don't use a pressure or power-washing machine. These are highly destructive to wood. The high-pressure water erodes the lighter-colored spring wood from between the darker bands of denser summer-wood. If you use a pressure washer a number of times, soon your new wood will look like a decades-old fishing pier.
I've had the best luck in cleaning using certified organic oxygen bleach cleaners that you dissolve in water. I apply mine in the shade to dry wood so the solution soaks deep into the fibers to help clean the wood. Don't use chlorine bleach or any product with sodium hypochlorite; it's so harsh it will remove the natural color from the wood, and it destroys the lignin that holds the wood fibers together.
The best way to minimize work with maintaining outdoor wood is to re-coat the wood before it completely fails. If you use a penetrating sealer, as I did a month ago, you may discover that in two years you should apply a thin maintenance coat. By then you may just have to do a mild washing of the wood much like you wash your car using liquid dish soap and water.
I did a little experiment this year to be able to gauge the wear of the sealer. I had to rebuild a few of my dock panels and had a few pieces of scrap cedar left over. I decided to seal those too and put them in my garage up on a shelf out of the sun and weather. Next spring, I'll take them out and put them on the dock to see how much the sealer suffered. As soon as I see significant wear, I'm going to do a maintenance coat.
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