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Sealing outdoor wood - oil or water? Whats the difference

Hey guys what should I use to seal the bottom side of my deck. The top is trex and the bottom looks like pressure treated wood. I dont know when this was installed but I pressure washed it clean and it has dried for the past two days... The guy at the paint store told me to buy wolmans raincoat water-based (blue can). Is this good for this project? What is the difference with oil-based, there seems to be much more oil based products out there. Is there a better product or is the wolmans water based ok?

Re: Sealing outdoor wood - oil or water? Whats the difference

You may get a lot of differing opinions when you ask for product recommendations. Treated wood should not need to be sealed, but it could use some cleaning. A little bleach/water and a brush, borax/water and a brush, TSP/water and a brush or laundry detergent/water and a brush will quickly remove the green slime.

As for sealing afterwards, you might consider a wood stain, either oil based or latex should work.

Re: Sealing outdoor wood - oil or water? Whats the difference

A cleaning product I have used for literally 40 years, is JOMAX by Zinsser. It is a quart of concentrate that is mixed with 3 quarts of household bleach and 4 gallons of water to form a total of 5 gallons of solution. If you load it into a garten pump sprayer and spray those deck joists, the green and black mildew and algae stains will disappear before your eyes! Then just rinse it with water. Jomax is available at Home Depot or good paint stores.

There are products that replenish the chemicals that are already in the pressure treated wood. Such chemicals prevent rot in that they are toxic to plant life. Rot is fungus ( plant life) that is eating away at the cellulose in wood. Kill the fungus and the wood does not rot! I suspect the Wolman product is in this class.

As Keith points out, pressure treated wood does not need a stain, at least for rot protection. Stains make the wood more attractive, and to some extent, slow down the drying out and cracking of the wood grain. However, that will eventually happen one way or the other.

If staining, I lean toward oil products., as they form no surface film, as do the latex based water stains. Where there is a surface film, there is always the possibility of peeling. The worst thing you could do would be to paint those joists!

Unfortunately, your deck builder did not use the vinyl joist tape before fastening down the decking. this prevents water from entering the top of joist trough the top. The tape has a gooey substance on the bottom which seals around screws or nails driven through it. Where wooden decking is used, it also limits the water passed upward into the bottom of the decking boards. Of course, the wooden decking is rarely sealed before being screwed down either, as it should be!

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