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How to Repair Rotted Wood

  • Transcript

    LESLIE: Well, everyone’s house is susceptible to rotted wood and it usually happens where wood meets water.

    TOM: Yeah. But rot isn’t just a condition; it’s actually a living, breathing pack of organisms that can wreak havoc on a home. Here to tell us more is This Old House general contractor Tom Silva.

    Welcome, Tommy.

    TOM SILVA: Thanks, guys. Nice to be here.

    TOM: You know, rot is sort of a term of art, right? People use it to describe just about anything that structurally goes wrong to a house. So, let’s start by kind of describing what’s actually happening when you find a piece of rotted wood.

    TOM SILVA: Well, you get rot when you have too much water around wood.

    TOM: OK.

    TOM SILVA: Long periods of time will rot that wood. And it’s actually a fungus that gets into the wood, it becomes mold or mildew and it starts by staining and so on down the line. And it actually ruins the integrity of the wood.

    TOM: So it’s really like the microorganisms that start to attack those fibers.

    TOM SILVA: Exactly. And when that starts to break down, there’s not a lot that you can do. You either have to cut it out or fix it.

    TOM: So, if we are going to fix it now, what’s the best way to sort of attack this? Is it just a situation where you’re going to use wood putty?

    TOM SILVA: Well, I wouldn’t use wood putty.

    TOM: OK.

    TOM SILVA: First of all, you have to eliminate the rot. You have to cut it out and you have to get down to bare wood. I use a two-part epoxy and that epoxy goes over a primer that you have to put on there first. And that’s a two-part system, also.

    So you have to dig out, rout out, whatever you have to do to get rid of the rot and then get to the fresh wood so you can apply this primer or Primatrate, they call it. And you apply it to the wood.

    Now, I have 10 to 45 minutes to work with that. So I mix up my epoxy. It comes in a two-part caulking gun. And there’s either a tip that will mix it or I can squeeze it out to a piece of glass. And I can mix it up with a plastic knife and then just plow it into that void.

    And I can build it up as thick as I want. I can either follow a molding profile and make it with that, overbuild it. And what I like to do when I – if I have a profile, I’ll actually take a plastic knife and I’ll make up the profile of the molding and then I’ll just trace it or scribe it right down. And then I just have to fine-tune it later on.

    TOM: Now, do you have to account for shrinkage? Do you have to do it in layers or can you just sort of one-and-done?

    TOM SILVA: Not with the type I use.

    TOM: OK.

    TOM SILVA: You can just build it right up and it’s amazing that – it takes about 24 hours, sometimes 40 hours for it to dry. But once it’s dry, I can rout it, I can sand it, I can grind it, I can form it, chisel it, whatever you want.

    TOM: Probably stronger than the wood it replaced.

    TOM SILVA: It is stronger. But the big deal is that it moves with the wood; it’s flexible.

    TOM: Right.

    TOM SILVA: And that’s very important.

    LESLIE: Now, does it ever get to a point where you sort of have to weigh whether it’s better to repair that wood that has the rot or just simply replace that piece?

    TOM SILVA: Absolutely. You want to definitely look at the cost because the epoxy is not cheap. In some cases, where you have a round column or you want to do a curved molding around the bottom, it gets expense to do that. But if I have a simple window casing at the bottom where it meets the window sill, it may be rotted. So I can – may be able to just patch in that little rotted end of the sill and fix the lower part of the casing.

    TOM: And that is the distinctive voice of Tom Silva, the general contractor on TV’s This Old House. We’re talking about rotted wood.

    Let’s talk about how you detect the difference between rotted wood and insect damage. As I said before, people call it all rotted wood but it really is a significant difference. And I think the key to repairing anything is knowing what causes it, right?

    TOM SILVA: Right. And the main culprit is water. Water is the enemy. When it gets into the wood and you get a certain moisture content, it will just rot on its own.

    TOM: Right.

    TOM SILVA: But if it gets into the wood and it’s the right location of the house and you may have carpenter ants, they’ll get into that wood because they like the moisture. They are wood movers and they will actually move that wood.

    A termite will get in and they are wood eaters, so they will eat the wood. The difference is termites don’t like the sunlight and carpenter ants don’t mind the daylight or the sunlight. And they just take the wood and they could move it 20 feet away.

    TOM: So if we’ve got rot and maybe we suspect some insect damage, we also need to make sure that we’re not only repairing the rot but treating the insects. Because you know how it is: if you see them in one place, they’re somewhere else.

    TOM SILVA: Maybe they’re somewhere else. Yeah, exactly. Exactly.

    And you could tell if the wood is eaten by insects because the grain of the wood, there’s all – there’s an open grain or a fast-growing grain and then a hard grain.

    TOM: Right.

    TOM SILVA: And they usually eat the softer grain.

    TOM: Right.

    TOM SILVA: And you can see it’s a thin, thin ring that – left around.

    TOM: Love that summer/spring growth; hate that hard, slow winter growth.

    TOM SILVA: Oh, yeah. Exactly, exactly.

    TOM: Yep.

    TOM SILVA: To stop rot, the main thing is primer and paint, all six sides.

    TOM: Yep.

    TOM SILVA: Get it in there and stop the water from getting around it.

    TOM: Painters always forget the fifth and the sixth side. That end grain is so critical because that’s so absorbent, right? Draws the water right in.

    TOM SILVA: Exactly, exactly. Yep.

    LESLIE: You know, Tommy, it’s funny. A lot of people will say the term “dry rot.” Is that …?

    TOM SILVA: Mm-hmm. I love that term.

    LESLIE: Right. Is it its own category of rot or is it non-existing?

    TOM SILVA: Well, if it’s its own category – if you mean that it’s dry rot, it’s rot that’s been caused by water that’s eventually dried out and so now it’s dry rot.


    TOM: It’s not a new type of rot; it’s the regular rot.

    LESLIE: So there’s not three different kinds? That’s just the next stage of it.

    TOM: Without the water.

    TOM SILVA: That’s the next step after it dries out.

    TOM: Tom Silva, the general contractor on TV’s This Old House, thanks for stopping by The Money Pit and filling us all in on the topic of rot.

    TOM SILVA: Well, it’s nice to be here. Thanks.

    LESLIE: Alright. You can catch the current season of This Old House and Ask This Old House on PBS. For local listings and step-by-step videos of many common home improvement projects, visit ThisOldHouse.com.

    TOM: And This Old House is brought to you by State Farm. Like a good neighbor, State Farm is there.

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