DEAR SAM: My outside walls are cinder block with brick veneer. I would like to improve the insulation. There are one-inch furring strips over the cinder blocks with rocklath and plaster for the interior walls. The one-inch air space between the furring strips cold be filled with insulation. But would there be condensation in the walls with no vapor barrier? This part of the house is one story with attic and crawl space.

ANSWER: If you are having trouble with cold interior walls, use Vermiculite or Micafil, but do not expect a vast improvement. Don't worry about condensation because wallpaper or paint will substitute.

Do cover the ground in the crawl space with polyethylene vinyl and insulate the floor joists with a six-inch-thick blanket or batts with the vapor barrier facing the warm side of the house.

DEAR SAM: I installed Armstrong ceiling tile in a basement recreation room several years ago. A number of the tiles have become water stained because of a leak in the floor above. Can the stains be removed?

ANSWER: Here are some suggestions:

1. Try using one tablespoon of washing soda in a pint of warm water and scrubbing with a clean sponge.

2. Take one of the tiles to your Armstrong dealer. He or she may be able to find a close match among the leftover stock or could give you some advice about finding a match.

3. Exchange the stained tiles for some good ones in an inconspicuous part of the room or a closet.

4. Make a center design, such as a square of rectangle, by putting down new tiles in white or a contrasting color in place of the stained tiles.

5. Using an artists' brush, paint carefully around the pattern in your tiles.

DEAR SAM: My bathroom ceiling was painted about seven years ago with epoxy gloss enamel. Over the years, it has developed bubbles as the result of water vapor and condensation. Several years ago the adjoining wall of the hallway was painted with two colors of green and recently I have applied expensive, one-coat white latex, but this paint has come off in large expanses. In both cases I'm afraid to sand the old finish because it might hurt the hard plaster finish beneath. I don't want to use paint remover.

ANSWER: The hard epoxy enamel on the bathroom ceiling should be sanded with an electric belt sander to smooth out the bubbles. Then the entire ceiling should be given a light sanding to remove the high gloss before applying the new epoxy paint. You need not worry about the plaster being affected by this sanding: Even if several cuts are made they can be easily repaired with vinyl spackling paste and a putty knife or broad knife.

The peeling in the hallway may be the result of incompatible paints. You could try to remove additional sections with a broad knife, especially if the the latest coat is thick. Otherwise, you could feather-edge with the sander before applying a new latex acrylic paint. Wash the wall first.

DEAR SAM: My L-shaped ranch house measures 48 feet along the front, 36 feet to the rear right side and 24 feet on the left side. The only place where water enters the basement is at the right rear corner, about six feet on each side; however, this occurs only during heavy rainfalls.It penetrates at the juncture of the floor and the cinder block walls. I have a sump hole and a sump pump on the left side, rear corner. How can I correct this condition?

ANSWER: Is there a French drain along the foundation floor of the L-shaped rear walls?

The pitch of the perforated, 4-inch asphalt pipe (Orangeburg) may be as little as 1/4-inch to 12-inch distance, but the French drain (trench) should be a minimum of four inches below the floor level and extend to the low point, where the sump pump is located, which could be about 18 to 24 inches below the floor level. Undoubtedly, the French drain is not operating correctly because of the pitch at this critical corner. Any accumulating water there flows in the direction of the existing pump.

DEAR SAM: Our large Thermopane window has several light scratches caused by using a faulty window cleaning tool. Is there some way to remove these scratches?

ANSWER: Depending on the depth of the scratches, it may be possible to "erase" them by using an electric drill with disc sander, covered with soft felt, which will be dipped into a solution of Rareox.

According to the manufacturer, (Sommer and Maco, Glass Machinery Co., Chicago) Rareox contains cerium oxide polishing powder and is suitable for windshields, stemware, mirrors and TV picture tubes.

The polishing felt is first saturated in water; 1 part Rareox powder is dissolved in 2 parts water for a light paste. The company emphasizes that this powder is not suitable for deep scratches.

Be careful not to splatter this polish into your eyes, nose or throat, as the powder contains a metallic compound. An auto glass dealer, who usually replaces or repairs windshields, might be more qualified to repair your window. He could also advise you whether the scratch is sufficiently light so that it may buffed away.Check the Yellow Pages under Auto Glass. He may, also be able to supply you with Rareox, if you are determined to do it yourself.