Q. You recently answered a question concerning indoor mildew problems. We have an outside mildew problem on the painted cedar siding of our home. Our home is only about 1 1/2 years old. How can we rid ourselves of mildew permanently? If we decide to repaint, is there some preventative substance that can be added to the paint?

A.Mildew attacks paint that is not formulated to resist its growth under climatic conditions that favor it. It is caused by airborne spores that are present nearly everywhere in warmer, more humid climates.

Prolonged warm weather and relatively high humidity favor mildew growth on unprotected organic material, especially when the surface is shaded from direct sun and has inadequate air circulation.

After mildew growth is established on a painted surface it is difficult to remove, although once it is eliminated new growth can be prevented.

The procedure is simple. You'll need a stiff-bristle scrubbing brush (do not use wire) and time to do a thorough job. Mix a solution of trisodium phosphate (1 cup), household bleach (1 cup) and warm water (1 gallon).

Apply the solution to the siding with a sponge. Immediately scrub the wetted surface with the stiff-bristle brush. When using this solution, wear rubber gloves and protect your eyes against splatters.

Continue scrubbing all surfaces affected until all the mold has been removed and the paint is exposed. It will take a lot of elbow grease to do the job.

When the surface is dry, immediately apply a coat of mildew-resistant paint. It's important that there be no appreciable delay between scrubbing and painting with the mildew-resistant paint, because washing off existing mildew does not protect the surface from a new attack.

You can buy paints that have a mildewcide at a good, well-stocked paint dealer, or you can buy an additive that can be mixed with any good exterior paint for protection against mildew.

Q. I have several area rugs in the kitchen and bath. They slide around and are dangerous. Is there anything you can recommend to make them stay put?

A. There are pads available for placing underneath area rugs to help them stay in place.

You also can coat the underside of your throw rugs with a rubberized product such as Fiber-Lok. It dries clear but remains slightly tacky to help keep the rug in place. It's machine-washable in either cold or warm water.

For the dealer nearest you, contact Environmental Technology Inc., P.O. Box 365, South Bay Depot Road, Fields Landing, Calif. 95537.

Q. I am in need of a method to clean the stained floor grouting on my kitchen and bathroom floors. I have tried diluted bleach without success. If cleaning is not feasible, is there some sort of paint that would be suitable?

A. The best bet for removing grout stains is a bleach-type poultice.

First, wash the areas to be treated with hot water and wipe dry, but while the grout is still damp, apply a thick plaster made of abrasive cleaning powder (with bleach) and hot water.

Apply up to one-half-inch thick if possible, and let stand for 24 to 48 hours. Remove with a wood paddle or plastic spatula. The treatment can be repeated if necessary. The powder can be reused for general cleaning purposes.

You only need to cover the grout but it will probably be simpler to cover the entire surface. Clean several smaller portions at a time, rather than the whole floor.

If this does not clean satisfactorily, I recommend that you apply a new layer of grout. This requires that you remove the top layer of the old grout, about one-half to three-fourths of an inch. Use a screwdriver or grout saw (available from your tile dealer).

Then you can apply a new layer of fresh grout. To protect from future staining use one of the recommended grout sealers. Your tile dealer can provide you with the tools, new grouting and recommendations on protective sealers. I do not recommend painting.

Send inquiries to Here's How, Copley News Service, P.O. Box 190, San Diego, Calif. 92112-0190. Only questions of general interest can be answered in the column.