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Pool Chemicals May Cause Concrete Walkway's Dust


Question: The concrete walkway around our built-in swimming pool seems to be flaking off. That is, when we sweep around the pool, we have a lot of dust. Is it normal for concrete to break down like this? Is there anything we can do to stop it?

Answer: The condition you describe is called dusting. It usually occurs within the first several months of when concrete is installed. Several things can cause it, such as using a concrete mix with a low cement content, using a concrete mix that is too wet, allowing the surface to dry too rapidly, freezing temperatures before the concrete is cured and finishing the concrete while bleed water is on the surface.

Since your concrete is 7 years old, we suspect it's being caused by the pool water being splashed on the concrete. Chemicals in the pool water, such as chlorine, may be reacting with the concrete.

Try the following. Remove the dust and clean the walkway by scrubbing the surface with a stiff bristle broom, then hose off the accumulated dust. Let the walkway dry, and be careful not to splash pool water on it. Next, coat the concrete with a sealer that contains methyl methacrylate or silane.

One such concrete sealer is Pakmix, and it's sold at home centers and masonry supply yards.


Q: The stairs leading from my deck to the ground have become shaky. What causes this, and what can you suggest to make them more secure?

A: A common cause of loosening deck stairs is heaving or settling, meaning the earth or pad that supports the bottom of the stairs can move. This loosens the attachment of the stair to the deck.

The first course of action is to readjust the bottom support of the stair. If your steps sit directly on the earth, shim the stringers with flat rocks or shovel new earth in place. If your steps rest on a masonry pad, you'll have to lift and shim the pad. Then, reinforce the attachments at the top of the stairs by driving toenails through the stringer into the rim joist.

Through use, the nails that hold the stringers to the stair treads can become loose. Use a long clamp to draw the stringers tight to the tread and drive new nails to hold the assembly together.

To submit a question, write to Popular Mechanics, Reader Service Bureau, 224 W. 57th St., New York, NY 10019. The most interesting questions will be answered in a future column.

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