Q: The plastic cut-outs that were applied to the bottom of our bathtub to create a nonskid surface have dried out and I am trying to remove them. It is a painstaking and laborious job scraping them off, and when I do there is still an ugly yellow outline on the tub. Is there an easier way to get them off? How do I remove the stain?

A: A razor blade will speed the job of scraping them off. Hold it almost flat against the surface to avoid scratching the porcelain. The yellow stain should come off with acetone or lacquer thinner (nail polish remover). If this doesn't work, scrub them off with a commercial tub cleaner such as Zud, which is sold in hardware stores and plumbing supply houses.

Q: My attic floor has about six inches of blown-in insulation on the floor. Can rolled insulation be placed over this to further reduce heat loss through the attic, and if so, is there any special procedure for doing this?

A: You can certainly place additional blankets or batts of insulation on top of the existing material. Either run them apparel to and between the beams, or across and on top of the beams. The second method gives the most protection against heat loss because it covers the wood beams as well.

One caution: Make sure the new layer does not have another vapor barrier (I'm assuming the original insulation has a vapor barrier under it). You do not want two vapor barriers. If there is none under the original material, it would be worthwhile to put one made of polyethylene sheeting under it, then push the insulating material back on top.

Q: The door leading to my bedroom is covered with wood paneling on the outside. It appears to be hanging level relative to the door frame and the floor, but when it is left in the open position, it slowly swings closed. How can this be corrected without using a door stop or a hook of some kind?

A: Since I don't know which way the door opens (in or out when standing in the bedroom), I cannot say for sure, but it could be that the weight of the extra panel on one side is unbalancing the door. It is also likely that the door is not hanging level -- that is, it probably is not exactly vertical to the floor when fully closed. This could be because the actual wall is not truly vertical or because the door frame is not vertical.

Either way, you should be able to correct this by resetting the hinges slightly so the top one is a little farther away from the stop molding than the bottom hinge is. This will move the top of the door slightly outward and overcome its tendency to swing shut. You may then have to reset the stop molding slightly.

Q: Our 15-year-old house was built on a cement slab. Recently we noticed that the floor in one room, which has the original asphalt tile on it, has begun to break down. Little bumpy sections or lumps appear in the back of the chairs and near the edges of the rug -- then they seem to grow. When we cut into one it crumbled. Can you tell us what this is, and what we can do about it?

A: This condition is known as effloresence, and is not at all uncommon in cement slab floors. It is the result of excess alkali in the concrete being activated by the moisture. The result is an accumulation of salts, which is the powdery residue that seems to be growing out of the floor. As a rule, this can be removed by washing it with a solution of muriatic acid (sold in paint and hardware stores). Mix 1 part acid with 3 parts water and mop on liberally, then rinse off thoroughly when it stops bubbling. This will get rid of the efflorescence and will enable you to patch the surface, but there is still no guarantee the efflorescence won't come back if the moisture problem continues.

Q: What can I do to remove motor oil from my concrete driveway?

A: Most hardware stores, lumber yards and home centers sell special driveway cleaners that usually do the job quite well. These cleaners are detergents that dissolve the oil and grease so they can be flushed away with water. Another remedy that often works is to cover the stained area with a fairly thick layer of dry, p owdered Portland cement. Saturate this with paint thinner or a similar solvent, cover with plastic to keep it from drying out, and allow it to set overnight. Then sweep it up. The powder acts as a blotter to absorb the oil.

Q: We recently converted from a forced hot-air to a hot-water heating system. We like the new system very much but there is a problem. When the heat comes on in the morning, the pipes often make a banging sound. The plumber says the noise is merely the expansion and contraction of the pipes when the warm water hits the cold metal, and nothing can be done about it. Is the problem more acute than this, and should something be done about it?

A: I think your plumber is at least partly right. Chances are the noise is caused by expansion and contraction of the metal pipes. But I'm not sure nothing can be done about it. The contraction can often be improved by rechecking the pipe mountings and fastening points to secure sections where the pipes can move easily, or where they rub or bang against structural members. Covering pipes with insulation sometimes helps to minimize the noise.