Q Our garage floor is deteriorating and the contractor is afraid of damaging the foundation if he removes it. He suggests placing a layer of 21/2 to 3 inches of new concrete on top of the present floor. Do you agree? A reader Washington, Ill. Three inches of new concrete will last a long time if poured over the old slab. Be sure to remove all loose concrete from the old slab and then thoroughly broom-clean it. Before pouring the new concrete, treat the old surface with a bonding compound that is available from most builder-supply outlets. It looks like a white glue. Q I have two questions: (1) Because of the attic flooring, we are unable to insulate effectively; also, the headroom is limited. Would it be wise to insulate the attic roof, or would this result in a heated attic, thus raising our heating bill? And (2) the surface layers of our long concrete driveways have flaked off, exposing the aggregate. We've been told that replacement is the only answer. Is there a more effective way of stopping the deterioration, such as overcoating with a new layer of c oncrete? John D. Burke Athens, Ga.
Insulating the attic rafters would help cut your heat loss. You would be heating a larger volume than if you were to lift up the attic flooring and insulate between the ceiling joists. If you decide to insulate the attic, use insulation that has kraft paper on one side or all around, so that your clothes do not pick up fiber glass when you brush up against it.
Your driveway problem seems to be the result of either improper curing or else a mix with too much water and too little cement.
You can top an existing slab with a minimum of three inches of new concrete. Any less will spall off too easily. This assumes, of course, that the existing slab doesn't have too many structural cracks.
The only other topping that I would recommend for such a large area is about 11/2 inches of asphalt. Q Our church auditorium has a very high ceiling (30 feet to the peak) and a very high heating bill. Heating is by means of an electric forced-air unit which has its duct registers about 12 feet above the floor. Would ceiling fans cut our electric bills? Walter E. Schooley Shavertown, Pa.
Fans would surely help move the hot air, now packed into the upper area of the auditorium, down into the lower area where it is needed.
For the quietest and most effective job, I'd use an old-fashioned, four-blade fan. While the movement of the fans might cause some comment when first installed, it will soon go unnoticed. Any other type of commercial air movers would be noisier and need some sort of concealment.
I'm really not sure what effect this will have on your heating bill, however. In such a large volume, the air will still tend to stratify to a degree, and heat loss through the ceiling could be your main problem. You might also try leaving on the fan on the forced-air unit. Q In an earlier column on mildew, you suggested that a house might be deodorized and disinfected by professionals. I can find nothing in our phone-book Yellow Pages. Can you be more specific? Janice C. Davis Hudson, N.Y.
In the Orange County, Calif., business-to-business Yellow Pages there is a heading, ``Deodorizing and Disinfecting,'' listing several local businesses. The only national-product distributor is Airwick Professional Products.
I am told that the company has distribution centers in most major cities. Its product, called A-33, is designed to control mildew, although fresh air and sunshine may be the only lasting cures. Q Fiber-glass insulation was installed between the joists in our basement ceiling with the foil facing the outside. Should the ceiling be covered with sheetrock, or is it sufficient to apply duct tape to any small area where the fiber glass is visible? Neil Hudson San Francisco
If the batts are fitted tightly to the sides of the joists, it is unnecessary to do any further work. The addition of duct tape or sheetrock will help, but only to a very small degree.
The fiber-glass strands not only create surfaces to which the air molecules can cling, but also form pockets of dead air space, which is the best insulator.
If you have a question about designing, improving, or maintaining your home, send it to the real estate editor, The Christian Science Monitor, One Norway Street, Boston, Mass. 02115. Richard A. Kent is a practicing architect and general contractor in southern California.