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Wednesday, Oct. 11, 2006 06:26 pm

Keeping mold off the roof

How to use and install zinc strips

Dear Gene: I have heard that zinc strips can keep mold from forming on asphalt-shingled roofs, but how are the strips installed and where can I get them?

Zinc strips are available in 3-foot lengths and in roll form. The manufacturer’s specific instructions should be followed when the strips are installed. In general, however, a strip of zinc spanning the width of the roof is installed near the roof ridge on each of the roof’s slopes. Tabs of shingles are lifted to nail the strip, so that nail heads are covered by shingle tabs. A portion of the zinc is left exposed, of course. Rain washing over the zinc causes a chemical reaction that inhibits the growth of mold and fungi such as mildew, which often leave ugly dark stains on shingles.

One row of zinc at the ridge is suitable for typical roofs, but a second row halfway down the slope may be needed if the slope is more than 20 feet or if there is a serious mold problem.

The roof should be thoroughly cleaned and allowed to dry completely before the zinc strips are installed. A source of zinc strips, roof cleaner, and more information is available at the Web site

Dear Gene: Our home is built over a crawl space that is very shallow — there is an opening about 30 inches by 24 inches. The floor over the space gets very cold in winter, and we would like to try and insulate it. Is this possible?

The crawl space can probably be insulated, but it won’t be easy in such a cramped space. The first thing you should do is to check out the floor of the space. If it is concrete, you’ll need kneepads to move around with reasonable comfort. If the floor is dirt, it should be covered with a thick plastic sheet before anything else is done.

There are a couple of ways to insulate a crawl space. If the space is fully closed off and contains pipes and/or ducts and is dry year-round, the walls should be insulated. If the space is well ventilated, the ceiling (the floor of the living area) should be insulated instead of the walls.

Blanket-type fiberglass insulation, sold in roll form, is generally used. An R-value of 19 (about 6 inches thick) is a good choice for most climate areas. The insulation should have a covering or vapor barrier. In all but a few warm-climate areas, the vapor barrier should go on the inside if walls are insulated and on top if the ceiling is insulated. In warm climates where air conditioning is used much of the year, check with local building-code officials to determine placement of the vapor barrier.

To insulate crawl space walls, staple lengths of insulation to the band joist, which surrounds the ceiling framing. Drape the strips of insulation vertically down the wall so each strip extends about a foot across the floor. To insulate the ceiling, stuff insulation between the joists and hold it there with lengths of stiff wire (sold by insulation dealers). Have a helper outside the crawl space cut the rolls of insulation into correct lengths and pass them to you. You will have to wear goggles, gloves, protective clothing, and a dust mask.

Dear Gene: Our basement has concrete-block walls that I would like to paint. The concrete has a white powderlike coating in spots. How do we proceed?

Your first step will be to remove the powder, called efflorescence. The powder is minerals that leach from your concrete blocks because of moisture in the blocks. I suggest using Drylok Etch ( to clean the walls. This is an acid wash, and you should read and follow the directions and cautions carefully. Once you have the walls cleaned, you can apply a waterproofing paint such as UGL’s Drylok or Zinsser’s WaterTite ( These paints are sold at many home centers and paint stores. Again, follow directions carefully.

Quick tip: A dripping faucet can cause a great deal of mischief — staining a tub or sink, making an annoying noise, wasting water, and even wearing off the finish if the drip continues long enough. The drip should be repaired as soon as possible, of course, but a temporary solution is to place a large bath sponge in the fixture to catch the dripping water. Wring the sponge out occasionally to keep it absorbent.

Send questions and comments to Gene Austin at or 1730 Blue Bell Pike, Blue Bell, PA 19422. Distributed by McClatchy-Tribune Information Services.

Copyright © 2006 Gene Austin