Brick turned powdery: best to leave it alone, perhaps

Q. At one time artificial stone was glued over the brick on my house. Now I notice that the exposed brick is powdering. What will stop this process? I do not know what kind of glue was used to cause the stone to adhere to the brick.

M.M. Knight

Park Forest, Ill.

A. We suspect the glue may have had nothing to do with the powdering of the brick.

The artificial stone veneer may have leaked. If so, moisture could have been retained on the hidden brick face. Frozen, that moisture in winter may have caused spalling.

It is so unusual to see brick covered with another product that it begs the question as to why. Perhaps there was a problem with the brick before the imitation stone was applied.

Depending on the age of the dwelling, it is possible that the brick was backup grade and not intended to be exposed to the weather. Before World War II, two distinct types of bricks were made, face and common. The Chicago area was particularly noted for underfired common brick.

Another possibility for the powdering is that in the process of removing the outer covering, the die skin of the brick was removed, especially if sandblasting was used. On a soft underfired brick, like the old-type common brick, the result would cause it to deteriorate rapidly when exposed to the weather.

What to do about the brick powdering now? The Brick Institute of America, McLean, Va., says: ''Probably the best advice is to take no action. The spalling should stop once the damaged surface is gone.''

The trade organization does not recommend your using one of the so-called waterproofing agents, particularly if it contains silicone.