JIM OFRIA, Lexington

A. Since chalk is made of limestone, then muriatic acid should do it in the wink of an eye. The acid attacks the lime in chalk; it also attacks lime in concrete, mortar, grout, and efflorescence (white stains) on concrete foundation walls. It is used to remove excess or spilled mortar.

Mix the acid half and half with water and apply it with a paintbrush, or pour it on the chalked areas. After it stops fizzing, hose it off. When mixing acid and water, always pour the acid into the water. And wear skin and eye protection when working with bleach.

Q. My front walk is in bad shape, after being replaced a number of years ago. There are holes in the concrete and I am very unhappy with it. One man suggested putting bricks in sand, but what about chipping of bricks and possible damage from a snowblower and other action?

ANNA McKINNON, Wollaston

A. A brick-in-sand walk is just the ticket, I think, partly because my front walk is brick in sand, and I have no problem with chipping bricks, although they will chip. That is the nature of bricks that are not mortared. But it doesn't matter, because any chips, while they might show bright pink when fresh, will weather in a few months to match the original brick. If the pavement is smooth and even, snowblowers will not touch it. And, if you get City Hall Pavers or other hard bricks, they will outlast you, me, and Moses. Go for it!

If you do put down brick in sand, it is better to remove all the old concrete. If the concrete cannot be removed, bricks can be laid on top of the concrete, but more holes should be drilled in the concrete to allow drainage. Also, the added brick will raise the walk, and the bricks must be secured at the edge of the walk so they don't start ``walking'' out of position.