Q: We had a Plexiglas skylight installed several years ago. Painters recently smeared paint on the plastic while painting around it. We have tried delicately to remove this paint without scratching the plastic, but so far have not had success. Have you any suggestions?

A: Buy a plastic scraper, the kind sold for scratching ice from an automobile windsheild. You should be able to scrape the paint off with this if you are careful. If this fails, here's a trick that may work: Buy some waterless handcleaning cream (the kind sold for cleaning hands after painting), rub some of it gently onto part of the paint, and let it soak for a minute or so, then, wipe it off with a dry rag after the paint becomes soft. Try a small spot in one corner before you go ahead with the whole job just to make sure it won't harm the plastic.

Q: My house has hot water heat with baseboard radiators in most rooms. Last year I had wall-to-wall carpeting installed. This carpet goes under the radiators and now is apparently blocking air circulation to the bottom of the radiators and thus lowering their efficiency. The carpet installer told me the builder should have raised the radiators higher, and the builder told me I should have the carpet trimmed so it doesn't go under the radiators. Since neither of them wants to do anything about this, can you tell me which one is right, and what I can do to correct this problem myself?

A: To some degree both are right. If the installer of the radiators knew carpeting was going to be put down he should have mounted the radiators slightly higher. However, if the radiators were already in place, and if there was not enough clearance under them to allow for proper air circulation, the carpet should have been cut so it does not go all the way under. The logical solution now is to trim the carpet around the edges where it goes under the radiator cover and is interfering with proper air circulation.

Q: I have a 16-inch by 26-inch empty metal sleeve for an air conditioner (through the wall) in each of two bedrooms. They are not in use and have only thin sheetmetal covers on the inside. It always feels cold near these sleeves. Am I losing heat through them, and if so, what can I do about it?

A: You are probably losing quite a bit of heat, especially if there is only a single thickness of sheet metal between the inside and outside. Remove the inside cover and stuff some 6-inch-thick fiber glass into the sleeve. If there is no cover on the outside to keep the fiberglass dry, fit a cover of wood or metal on the outer end of the sleeve and caulk around it to ensure a watertight and airtight seal. Then replace the inside cover and check the caulking around the entire metal sleeve on the outside to seal off any air leaks.

Q: We leave our house vacant for a few months every winter, and from now on plan to leave it unheated. A plumber we consulted advised that the poured concrete foundation would crack if the house is unheated. Is this a realistic danger?

A: I cannot see any validity for this claim. If the foundation were to crack because of freezing temperatures, it would crack anyway because indoor heat does not necessarily keep the concrete foundation warm, especaially the part that is already underground. Many concrete walls and other structures are continually exposed to low temperatures year after year without damage, so unless there is a structural defect I don't think you have anything to worry about.

Q: About six months ago I painted my cement floor after washing it. I did not use a sealer, which was apparently a mistake because now the floor gets very dusty due to dust coming through the paint. Can I now put a sealer over the paint, and then paint again?

A: As a rule, deck paint for use on cement floors does not require a separate sealer, but does need at least two coats if it is to last. Assuming your deck paint is not peeling, I suggest washing it again, allowing it to dry, then repainting it with one or two coats on top of the old paint. Chances are you didn't put enough down the first time.

Q: Ihave white asbestos shingles on the outside of my house. These have become dirty and stained and I think they have mildew on them. What kind of cleaning is required, and what type of paint should I use?

A: Scrub them with a detergent if it is just dirt. If it is mildew, wash them with a solution of 1 part fresh liquid laundry bleach and 3 parts water. Add a few handfuls of powdered detergent and scrub them with this. Allow to dry on the surface, then rinse off with plenty of water. Paint with latex masonry paint that stipulates it is suitable for use on asbestos shingles, but use the primer recommended by the company for the first coat.