The Rot Doctor


Subject: (Carport/sillplate)
Date: Wed, 03 Jul 2002

Dear Dr. Rot

I hope you can help me with my problem. I recently built a carport that was anchored to an existing slab floor. When I built the stud walls, I failed to use a pressure treated or a redwood two by four for the bottom base. The wood was not kiln dried, so there is some moisture in the wood. And I'm afraid I will soon have dry rot in the two by four.

Is there any way I can treat that two by four where it is anchored in place to prevent rot problems in the future? The walls are open, so I can get all around them. I was thinking of drilling some small holes in the two by four between the studs to help dry the wood .

When I set the walls up I put a strip of tar paper on the bottom and up the sides so the two by four is encased on three sides with the paper. What do you suggest ? Is there any place in my area where I can buy the material you may recommend? Thank you.

First the easy part. We distribute our products only through mail order, so we would ship them to you UPS.

Now on to your problem. First, I wouldn't drill any holes to dry the wood out. It will dry out on it's own. Your situation is similar to what people with decks face. The problem is keeping any additional moisture from getting into the wood.

With decks, there are several main areas that commonly cause problems. One is the nails that join the pieces of the deck together. The water wicks between the nail and the wood, then soaks into the middle of the wood and takes a long time to dry out. Another place is where two pieces of wood touch, or as in your case, where the wood touches the slab. The water wicks between the wood and the concrete, but when the rain stops and the sun comes out, it can't dry out easily, giving the water more time to soak into the wood. Lastly, we have end grain. Water absorbs much easier into the end grain of wood than anywhere else. If you have a place where end grain is touching something else, another piece of wood, or concrete, look out.

In your case, you have a sill plate that is wrapped on the bottom and sides with tar paper. I'm guessing that this is tacked/nailed in place on the sides. As long as the tar paper lasts, this will protect fine against ground flooding. If the sill plate gets any water hitting the top of the wood, I think that the tar paper will actually make the wood rot sooner. Instead of keeping the water away from the wood, the tar paper is now holding the water against the wood. If the tar paper is nailed down, the nail holes will help the water to get into the wood. So unless water is never going to hit the top of the sill plate, I would get rid of as much of the tar paper as is practical.

Then I would take some CPES and one of our injection kits, and everywhere that the wood touches the concrete/tar paper, everywhere that wood touches more wood, everywhere that there is a nail, I would use the injection kit to shoot CPES into the cracks and wet the nails. Anywhere that water is going to get in and sit. Start at one end, go to the other end, then start again from the beginning and put on some more while the first application is still wet. Wait a day, then put on another application, this time only doing it once. I would probably wait a day and do one more application, this time taking a cheap china bristle brush and coating the whole sill plate, and as far up the studs as you expect water to get to.

Once this cures, you will have a sill plate that has one coat of CPES on the top and sides, and three coats at any cracks or nails. By having one coat of CPES on the top and sides, rainwater will run off, but any moisture that is in the wood already will still be able to come out. If, over time, any cracks develop in the wood, I would take the injection kit and put some CPES into the cracks to keep any water from getting into the wood. This will protect the wood as well as if you had used pressure treated wood, or better.

Let me know if you have any further questions.