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Posted: Saturday, Sep. 06, 2008

Spalling is cause of concrete pops; try a bonding agent in fix

Do It YourselfPeter Hotton
Published in: Home & Garden

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Q. My concrete block foundation is 28 years old, and some of the brown solid color latex stain is flaking and peeling, both inside and out. I can handle that, but in a few blocks on the outside large chunks of concrete are popping off the blocks. Some are an inch deep, or nearly so. Would that be due to moisture? And does that mean that the blocks are filling with water? I tried filling the popped areas with mortar without success.

It is unlikely that the blocks are full of water, but to find out, drill a hole in a block near the floor, and possibly high up, too. If you get water, you can drill holes here and there to drain it. More important are the chunks of concrete popping off the blocks. This is called spalling, where water vapor gets inside the block and condenses, then freezes and expands, popping off chunks willy-nilly. It also happens with bricks, where a small flaw allows water vapor to get inside the brick, then condenses into water that freezes.

Filling in the spall areas didn't work because you did not use a bonding agent before applying the mortar. To do it right, put a bonding agent on the spalled areas, then fill with Top ‘n' Bond, which is designed to go on in thin layers. Bonding agents are found where concrete products are sold and other outlets.

Q. I have old Jeld-Wen windows, about 20 years old. I have to replace some of the jamb liners where the tiny ropes have broken. I checked with the manufacturer who said they do not make anything older than 15 years old. Is there any place else I can find them?

There is a wholesale outfit called Brosco (Brockway-Smith) that carries everything for the house, including windows, except lumber. Go to an independent lumber dealer who will show you a catalog that contains two pages of balances for windows. If you find one that works, the dealer will order it for you. You can probably keep the catalog. In the meantime you can hold the windows open with a stick.

Q. I had my builder install zinc strips at the top of my roof to help prevent the growth of mold, lichen, moss, and algae. But now the strips, which are exposed 1 inch beyond the topmost shingles, are bubbling up, and look terrible. What's wrong?

I have recommended zinc strips many, many times. To elaborate, when water runs over the strips, it picks up a bit of the zinc and distributes it downroof, preventing the growth of mold and algae. They may be defective, and aggravated by the salt in the air and water. You might try getting another set of strips. Using another kind of metal such as copper, which is deadly to mold and algae, is not a good idea because the copper will turn to that familiar green color, which is OK on gutters, flashing, and other outside features, but not when it drips down the roof.

Q. My patio has many concrete patio blocks – green, red, and buff – which are in good shape but look rather dull and dingy. How can I restore their color ?

Simply power wash them. The color may come back and they will be clean. Or, put a cup of bleach in a gallon of hot water and wash the blocks. Or, turn one block over and hose it off; you will find the colors brighter, so you can turn them all over. But this all depends on whether the blocks are mortared.

Peter Hotton: The Boston Globe, 135 Morrissey Blvd., Boston, MA 02107; p_hotton@globe.com.

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