Q: The concrete floor in the basement of our 70-year-old house has a number of hairline cracks that normally are no problem. However, after the heavy rains of the past months, water has seeped in through these cracks. After several days, the floor dried and there has been no further problem. But, we do want to store things on the floor and are afraid of a recurrence. Is there any paint or coating we can apply that will keep the water out in the future?

A: The first thing you should do is try to fill the cracks in - if they are large enough for filling. If they are just hairline, as you say, you might try coating with an epoxy basement waterproofing sealer. This is a two part coating that is often used to seal cracks in masonry walls - but floors are a tougher problem. However, it might be worth trying since I don't know of any other coating that has even a chance of resisting the pressure of leaks through the floor.

Q: Some time ago, an open porch on our stucco house was enclosed, with glass in the winter and screens in the summer. There is a coat of white paint on the stucco, which was apparently applied over a green paint, but we don't know what type of paint was used. The white is peeling badly in places. After brushing off all loose paint, what else should I do to prepare the stucco for fresh paint, and what kind of paint should I use?

A: Since only the white top coat is peeling, it would be best if you could get as much of this off as possible. Use scrapers and a wire brush. Then I would advise using a coat of oil-base masonry primer, followed by an alkydbase masonry paint.

Q: Our house has a large, uninsulated attic which we plan to insulate. If we plan to eventually put up walls and convert this attic into a playroom, where should we put the insulation, and how thick should it be?

A: Since you intent to put up walls, the insulation should go up against the roof rafters, with a vapor barrier facing downward. For efficient protection, this insulation should be rated at a minimum of R-19 (about 6 1/2 inches thick).

Q: From time to time, we get a reverse flow of air through the chimney of our fireplace even though the fireplace is cold and the damper is closed. This brings a smell of dead ashes and soot into the room. Can you tell me what I can do to correct this situation?

A: By reverse flow, I assume you mean a downdraft. If so, there are several things that can cause this. One is, if the chimney does not project at least three feet above any ridge or other part of the roof that is within 10 feet of the chimney. Sometimes, installing a hood over the top of the chimney will cure this. Another cause do downdraft is a tall tree or other structure higher that the chimney, which less than 10 or 12 feet away. To eliminate the smell you are getting I would suggest checking the clean-out box or pit in the basement under the fireplace - it is probably full of old ashes that are causing the smell. It is also possible that your chimney flue needs cleaning and that the damper does not fit as tightly as it should when it is closed.

Questions about home repair should be addressed to Do-It-Yourself Clinic, The New York Times, 229 West 43rd St., New York, N.Y., 10036. Only questions of general interest can be answered in this column.)