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Handyman on Call

Moisture, poor design caused window sills to rot

By Peter Hotton
Globe Correspondent / July 25, 2010

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Q. We have windows (three crank-open windows and one picture window) that have rotted sills on the outside. Do we have to replace the whole window, or can we just replace the outside sill? The picture window also appears to be rotted on the bottom edge of the frame. We are not sure what has caused the rot.

PAT, anxious to hear your answer

A. It was moisture in combination with a lousy design that did not allow the window trim to drain; instead, it trapped water in joints and other inaccessible areas. Most sills can be replaced, and some can be filled with a wood rot filler, a two-part epoxy filler. The crank-outs (casement windows) might be difficult, but this is how it’s done.

Take off the inside sill, and take the window off its hinges, and unhook the crank. You may have to cut the sill from the vertical frame on each side. Use a Japanese saw, which allows you to cut flush at the bottom of the frame. There may be nails present, so you need a hacksaw to cut them. Now, cut the exterior sill in half, sideways, and pry each piece out carefully with a pinch bar or flat bar. Save the pieces.

Buy a pressure-treated 2-by-10, cut it to length, then use the two old pieces as a template to cut the sill to match the old. You may be able to buy a stock sill, but a pressure-treated one is better. Pull or cut all nails that are left. Now, insert the new sill. If the new sill is thinner than the original, you will have to add shims to bring the new sill into the right position, under the vertical frame. Or, nail a thin piece of plywood or hardboard on the bottom of the sill to match the thickness of the old.

The picture window may be tougher because you have to take out the window. As for the rotted places, you can dig out the decay and apply a wood hardener (made by Minwax). Then fill the opening with Minwax’s wood rot filler, a two-part epoxy that begins to set in just a few minutes, so you have to make small batches and work fast. If it begins to set before using it, throw it away and make a new batch.

One more thing: You might be able to cut out the decayed part of the sill, and insert a pressure-treated patch piece. Caulk it well and it can last for years.

If you have the time, doing all this is a sight better than buying a new window.

Q. My son bought a ‘93 house in Marshfield that has only a 4-foot-high crawl space on a concrete slab because the house is on a flood plain. The previous owner put insulation between the joists, with the paper backing (a vapor barrier) up, touching the ceiling above, and held in place by friction and pointed wires. Some of the insulation is sagging, so my son plans to put Tyvek on the joists to prevent that. Some friends told him not to do that, because the Tyvek is a vapor barrier and there should not be two vapor barriers in place. Is that so?

ROGER ALVEY, Marshfield

A. It is not so. Tyvek is not a vapor barrier, but will allow water vapor to go through it in both directions. Go ahead; that Tyvek will help hold the insulation in place.

Q. Your report about the artillery fungus, which shoots oily spores from wood mulch on the ground as much as 15 feet, and can stain siding, scared me a bit. My condo complex is surrounded by wood mulch, right up against the buildings. How long before we see the artillery fungus?

ROD MASON, Lincoln

A. How long? Maybe tomorrow, maybe in a year, maybe never. If you do get it, replace the wood mulch with crushed stone.

Q. Our 1973 house has a concrete ramp connecting the asphalt driveway to the garage. The concrete has a wide crack in it. One looks like an expansion joint with a wood form still in it. All are three-quarters to 1 inch wide. They were open when we bought the house, but a relative filled them with a driveway patch, which he covered with gray caulk. Both materials are now falling apart. What should we do with them? We want to protect the concrete from water and freezing damage but also have something that looks nicer.

BRIAN NIECE, Worcester

A. Dig out all the ugly stuff, and fill the gaps with stone dust or fine sand. They will look better than those present joints. Leave the wood form in the expansion joint.

Q. I read about the steel posts supporting basement beams in your column. I think there is concrete inside my columns, and I have the same trouble with them rusting away. If they are filled with concrete, would they last longer?

CURIOUS

A. OK, concrete filled steel columns are called Lally (columns), a trademark term. Filling the tube with concrete will make it stronger than an empty tube, but if the steel rusts out at the bottom, the concrete alone is not strong enough to support the beam. It should be fixed, and since it is structural, you need the assistance of a structural engineer to replace it, or have a professional do the work.

Globe Handyman on Call Peter Hotton is also in the g section on Thursdays. He is available 1-6 p.m. Tuesdays to answer questions on house repair. Call 617-929-2930. Hotton (photton@globe.com) also chats online about house matters 2-3 p.m. Thursdays. To participate, go to www.Boston.com.