Q: We have a yellow, molded fiber glass chair that has some smears of silver paint on it. How can we remove the paint?

A: You should be able to wipe the paint off easily with lacquer thinner or acetone. These solvents will not hurt fiber glass. But if the chair has been painted, the solvents will take that paint off, too. Test the thinner on the bottom of the chair where it will not show, just in case there is paint on the surface or if the chair is not really fiber glass.

Q: We moved into our Alexandria, Va., high-rise condominium three years ago. One of the selling points was that the building had all-steel beams and studs in the walls. However, starting about six weeks ago, dark stripes or streaks have developed on one western wall that look almost as though the studs themselves are showing through. The builder's representative looked at it and informed us this is the result of the building settling, but I don't believe it. Before we repaint, can you tell us the cause and what we can do to eliminate it?

A: This is obviously an outside wall, so I think the reason for the streaks is there is little or no insulation outside the metal studs -- all the insulation is between the studs -- so they get quite cold by conduction when temperatures drop on the outside. The cold is conducted by the metal to the inside wall surface, which also gets colder along the same line.

This, in turn, causes small amounts of condensation to form on the colder face of the wall along these lines, so the dust normally in the air tends to stick to these moist areas. This eventually forms the lines of dirt you see. Before painting, wash the streaks off with detergent. Chances are they will come back in a few years unless more insulation can be added to the walls. Dusting or wiping the wall periodically will also help.

Q: I recently had insulation blown into the attic. The workmen who did the job built the layer up above the level of the eaves and closed off the openings to the outside that had been there before. The insulation used is very porous, consisting of some type of particles about 1/2 inch in diameter. If I leave windows in the attic slightly open, is this enough ventilation?

A: I seriously doubt it, though it is hard to say for sure. If the eaves originally had oepnings these should definitely not be covered over with the insulation. You should have it scraped back and even erect small barriers to keep the material from drifting back over these openings. You should also have vents up near the peak of the attic or along the roof ridge in addition to these openings to provide adequate attic ventilation of the space above the insulation. If you do not have such additional vents, watch for signs of condensation in cold weather; if you see any, leave the windows slightly open -- or add vents near the top as described above.

Q: I have to varnish many wood surfaces around my home. I've been told I cannot apply varnish over shellac and some other finishes. How can I tell what kind of finish is on the wood, and what preparation, if any is required?

A: although shellac is not the best base over which to apply varnish, you can varnish over a shellacked surface. Just be sure you clean off all the wax or polish, and then sand till the surface is dull before you apply the first coat of varnish. This would also hold true when applying varnish over lacquer and most other finishes. The only finish you can not apply varnish over a wax finish -- or a surface that has been waxed or oiled.

Q: Our family room is built on a concrete slab and is constantly cold in the winter. The room is farthest from the furnace. We have storm windows and doors, with weatherstripping. It has been suggested we have a trench dug around the outside to a depth of three feet and then have stryofoam insulation placed against the foundation of this room. Is this apt to help much, or is there a better way you can suggest?

A: The most effective way to insulate a slab floor is to place rigid insulation under it -- and this means having the job done before the slab is poured. Since you already have a room built, this is obviously impractical. However, perimeter insulation does help somewhat, but there is no sense going down three feet to the bottom of the foundations where there is no crawl pace or basement under the slab. I would just go down about four to six inches to cover the edges of the slab. If part of the slab's edge is above ground, cover this too with rigid insulation. I can't say how much this will help, or even whether it would be worth the expense, but some heat will be saved. To keep the room comfortable in very cold weather, you may still find it advisable to add more heating units.

Q: I have read about the advisability of adding insulation to basement walls down to about 24 inches below ground level. My basement walls go down below the grade level about 12 inches, then the wall steps forward or thickens out by an addition 6 inches. Would it be enough to apply insulation down to the point where the wall forms this six-inch shelf?

A: Although insulation should ideally come down to about 24 inches below ground level on the inside, bringing insulation to about 12 inches below will help a great deal in the winter, especially if the basement is heated. The shelf in your foundation wall makes a natural stopping point, so I would settle for insulation down to that point.

Q: Our house has a large studio at ground level, which has a slate floor that has no shine and is hard to keep clean. This room is heated by hot water pipes that are buried in the floor under the slate. We would like to apply a coat of stone sealer to the slate floor but wonder what will happen to the sealer when the heat is on. The floor in an attached room was treated with something by the previous owners, and this has turned white in the joints. Will the same thing happen if the slate in the studio is treated?

A: I don't know why a good quality stone sealer should turn white from the heat under the floor as long as it was applied while the heat was off, and as long as the floor was thoroughly dry when the sealer was applied. White stains usually indicate dampness was present in the floor before the sealer was applied. If in doubt, try a small section first to see how it takes and to see if any such problem occurs. Let this remain for a week or two with the heat on. If nothing happens, go ahead with the rest of the floor.

Q: We are planning to sand our red oak hardwood floors, but want to know if it is necessary to stain them, and if we should use a shellac or a sanding sealer on them afterward?

A: Staining is not necessary. It is a matter or personal perference based on whether or not you want the wood darker than it naturally is. As far as a finish is concerned, this too is really a matter of preference. Shellac is quick-drying and gives a high gloss, but it shows scratch marks and turns white if spilled liquids are not wiped up immediately. A penetrating sealer is slower drying and gives a satin-finish, oiled appearance that will not show scratch marks. It is also generally easier to touch up and maintian.