Rot happens, even to the best of houses. All it takes is wood, water, and warmth, and before you know it solid lumber turns to mush. Exterior trim is the most vulnerable to attack by rot fungi, and it doesn't have to be very old; the trim shown here was installed only 10 years ago.

Fortunately, rotted trim is generally easy to repair. (Rot-infested framing or mudsills pose a much bigger problem.) But before you can fix it, you have to find it. Check out the horizontal areas that don't drain well and places where the paint is cracked, peeling, or blistering or the wood is darker. If your screwdriver pushes deeply into a suspect board, it's time to root out the rot. Pay particular attention to joints, which dry slowly, and to all wood that's close to dirt, concrete, or masonry.

For a relatively confined area, a two-part epoxy resin is a smart option that yields a seamless repair for pros of all levels. Here, John Stahl of Advanced Repair Technology, who restored the old windows for This Old House TV projects in Milton and Salem, Massachusetts, takes us through a typical repair of a rotted window mullion.

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