Q: The bowl of my white porcelain sink has turned quite yellow during the past year. I have tried all kinds of cleansers, but to no avail. We have hard water and I think this caused the discoloration. Can you recommend how to remove it?

A: If hard water is the problem -- though it usually does not leave a yellow color -- you should install a water softener. If ordinary cleansers do not work, try Zud, which is sold in hardware stores and plumbing supply houses, and often works where others fail. If the yellow stain is rust, try Iron Ike, a rust stain remover sold in plumbing supply houses. If the stains are rust, adding a water filter to your system will prevent it.

Q: I repainted a wall that had peeled due to a water leak. (The leak was repaired first.) Now the surface where the leak occured is uneven because of the indentations left when the paint peeled. How can I get a smooth surface again?

A: The usual way to fill these spots is with spackling compound. The ready-mixed vinyl or acrylic type is easier to use on thin recesses of this kind. Spread on with a flexible trowel, wiping off the excess to bring it flush with the surrounding plaster, then sand lightly when dry. A word of caution: If there was a leak, the plaster may have gotten soft and crumbly and, if so, patching over this will do no good. You have to scrape out all the softened or crumbly material first.

Q: When my house was built eight years ago the metal gutters were painted, but the following year they all peeled. Each year since, they have been repainted by professional painters who assure me that they have solved the problem. But each year the paint flakes off again. Can you suggest a solution?

A: If your gutters are made of galvanized steel, chances are the metal was never properly prepared and primed in the first place. Galvanized metal must be thoroughly cleaned with a solvent when the metal is new, then coated with a metal primer specifically formulated for use on it. Failure to clean off the oils left during manufacture or to apply the correct primer will cause a recurring peeling problem. Strip all the old paint off, wash with a solvent, prime as described above, then repaint.

Q: Our house was built in 1910 and has a stucco exterior that is now quite streaky and grimy in many places. We want to clean it. We have checked with sandblasting contractors in this area, but they tell us they will work only in unoccupied, boarded-up houses. Can you offer any suggestions as to the best and safest method of cleaning the stucco?

A: Sandblasting is generally not a good idea on stucco because of the damage it might cause to the finish. The stucco can be scrubbed clean with conventional detergent and water, using long-handled brushes and even scrubbing by hand. This is quite an undertaking on a large house, but it can be done.

You may want to consider calling one of the services that specializes in steam-cleaning building exteriors. This method is safe and usually effective on old, dirty masonary buildings, including brick and stucco. Although most of these companies specialize in commerical buildings, you may be able to find one to do a private house.

Q: I am planning to finish my basement soon. The walls are poured concrete and I plan to put up studs and then panel with Sheetrock after putting fiber glass batts between the studs. However, I am concerned with water seepage through the walls. Is it better to seal the walls with roofing cement, or to use cement-base coating.

A: You don't say you have a visible seepage problem now or whether you just want to play it safe by adding a sealer on the inside of the walls. If there is seepage, make sure it is eliminated before you start finishing the inside. Sometimes sealers will work when applied on the inside of basement walls, but not always. Stronger measurers, such as the installation of drain tile and a sump pump, may be required. This is easier to do while the basement is still unfinished.

Either way, roof coating is of little or no use as a sealer on the inside of basement walls. A cement-base or epoxy-base sealer specifically made for basement walls will be much more effective, but even these are able to stop only minor leaks, not serious ones.

Q: We have an 8-foot by 4-foot crawl space with an earth floor. The space is enclosed with brick and stucco. Above this crawl space fiber glass batts are fastened to the floor of the den above. This insulation has an aluminum vapor barrier that is away from the warm side. Is it necessary to cover the earth floor in this crawl space with polyethylene sheets, or will this create a nesting place for insects?

A: Any crawl space with an unpaved floor should be covered with some sort of vapor barrier -- either polyethylene or heavyweight roofing paper -- to keep moisture from seeping up from the ground. The insulation under the floor above this crawl space should have its own vapor barrier, but in your case, the barrier (the aluminum facing) is on the wrong side; it should always face the warm side of the insulation. A final word of caution: In addition to covering the floor of the crawl space you should provide ventilation by installing louvered vents on opposite facing walls.