Q: The grout between the ceramic tiles in the bathroom of the house we recently purchased has discolored over time. The tile is a light gray, and I believe the grout was originally an off-white. Now it is a dirty mottled color.

Is there any way I can restore the off-white grout so that it will look new again? -- A.E.

A: Try cleaning the dirty grout with a paste made by mixing scouring powder with bleach. Avoid products that may contain ammonia. Scrub this paste into the grout with a toothbrush, then rinse with clear water.

For stubborn stains, leave a mixture of the paste on the stained grout overnight, covered with plastic wrap to retain moisture. Remove the paste the next day and continue cleaning.

If the grout is still unsatisfactory, I have two other suggestions. Assuming the grout is in good condition -- that is, not flaking and crumbling -- you can use one of the newer grout stains and stain the grout a darker color, perhaps a charcoal gray to go with the lighter gray tile.

Manufacturers claim that the stains will work even when a lighter stain color is applying over a darker grout. Another remedy is to remove about a one-eighth to one-fourth-inch layer of the grout and then regrout with a new layer, choosing any grout color you prefer.

A grout saw can be purchased from a tile dealer for removal of the surface layer (or use a sharp instrument, such as a screwdriver). Grout stains are also available at your local tile dealer.

Q:Within the last six months we purchased a marble sink and counter for a bathroom. Recently, small cracks are appearing on the surface, particularly next to the drain. They seem to be getting worse and more are appearing.

What can I do? Was the sink and counter unit defective? And, if so, how do I go about getting the manufacturer to replace the sink? -- C.F.

A: Sometimes very hot water can cause surface cracks. However, it is more probable that the cracks are due either to a defective unit or improper installation.

Over-tightening the drain fitting with a wrench, rather than making it hand-tight, could cause the cracking. The condition cannot be repaired. If you had a contractor complete the work for you, contact him regarding the situation and replacement of the unit. If it was a do-it-yourself project, write the manufacturer and see what type of warranty might apply.

Q: How can quarry tile be treated to keep it looking nice? We have it throughout our house -- foyer, kitchen and bathroom.

We tried H.B. Fuller Sealer, then Val Oil No. 30 Clear. Both peeled after a few days. We then tried Lestoil and baby oil. We have been told to try terrazzo sealer, but we are afraid this will peel off, too. Do you have any recommendations? -- T.R.

A: First I would suggest a thorough cleaning to remove all residue of previous products.

Try scrubbing with warm water and an alkaline cleaning powder. First wet the floor liberally and then sprinkle the cleanser on freely. Let set a minute or two and then scrub with a synthetic scouring pad under a floor machine. Rinse well and let dry.

A coat of terrazzo sealer would be very beneficial. Scouring powders are not recommended for the routine maintenance of floors. While they have no effect upon the tiles, they can damage the grout. Your local sanitary supply dealer can recommend a cleaner.

Quarry tile is a natural product and does not produce a highly polished look like a ceramic tile. This may be the source of your disappointment with the tile. Terrazzo sealer will make it somewhat more polished looking, but your quarry tile will not produce a high shine.

Send inquiries to Here's How, Copley News Service, P.O. Box 190, San Diego, Calif. 592112-0190. Only questions of general interest can be answered in the column.