DEAR MIKE: I have noticed a white powder around the edges of my concrete walkway. Should I be concerned? -- Bob S.
DEAR BOB: You should be concerned if the DEA comes knocking on your door.
The white powder is the result of efflorescence, which occurs when a soluble salt, such as earth, sand or rocks is present in an environment of evaporating water.
Efflorescence can be seen in many places, such as on block walls where it appears as white stains or powder. It often looks like fresh snow.
Water carries the soluble salts through the masonry or pulls it from the surrounding material to the surface. The water evaporates but the salt does not, leaving you with the "just snowed" look.
Efflorescence can stop on its own if the supply of soluble salt in the masonry or surrounding material is depleted, or if the area stays dry. With our limited rainfall and poor drainage, salts are not leached out of the soil. Add landscape irrigation to the mix and you have the environment for efflorescence to flourish.
You may notice that the surface of your walkway or block wall has become etched from this occurrence. As the salts crystallize, they expand and place pressure on the surface of the masonry, damaging it.
There are several ways to remove the white staining of efflorescence. A stiff brush or broom can remove a lot of the white stuff. If that doesn't do the trick you can wash it away with acid. Pour a mixture of vinegar and water over the affected area. You can also add some organic material to the surrounding soil.
I advise against applying sealer on the concrete until efflorescence has stopped. If you seal the masonry while the salt is still crystallizing, the pressure will build up and could damage the surface.
A gallon of concrete sealer costs less than $20 and will cover about 250 square feet. It will typically penetrate to a depth of about one-half inch and can last for 10 years before you need to reapply it.
It goes on like paint. Pour some in a tray and roll it on the surface using a one-half inch thick roller. Work it into the pores and let it dry.
If the DEA agents come knocking, just hand them the paint tray and roller.