Q) Recently, we replaced plywood flooring on our outdoor deck with redwood. The plywood had deteriorated to the danger point. What can I do to preserve the redwood? Should I use paint, stain, varnish or linseed oil? I would appreciate your advice. -- J.J.T.

A) Redwood is one of the most carefree materials for exterior wood surfaces. It has an exceptional weather resistance and will serve a variety of exterior uses in even the most severe climates. The wood can be left untreated and allowed to weather naturally.

In damp and humid climates, the wood will darken within a few months. As time goes by, this darkening may be rinsed away by rain and the redwood will eventually weather-bleach to a soft driftwood gray.

In drier climates, unfinished redwood may not darken. Instead, the wood will gradually turn a silver tan.

If you want to treat the wood, the California Redwood Association recommends the use of a water repellent over other natural treatments. A water-repellent finish will not alter the rich, natural grain and texture of redwood. One of its biggest advantages, however, is that this type of finish modifies the effects of weathering, eliminating the dark stage that redwood sometimes goes through. It also slows the fading process. The wood gradually changes from its reddish brown color to a buckskin tan. It should stabilize at a light tan, but it may bleach to a silvery grey where exposed to falling water.

Two coats, applied with a brush, are recommended for new wood. The best results are obtained when the first coat is applied to the back, face, edges and ends of siding before it is nailed in place. If the wood is exposed to frequent wetting from any source, reapplications probably will be required.

One sign that it's time for an additional treatment is darkening of the wood. Quality water repellent contains a chemical to prevent the growth of mildew.

To achieve the best results, purchase only quality finishes manufactured for wood exteriors, follow the manufacturer's directions, apply to wood surfaces that are clean and dry and avoid windy, damp or extremely hot weather that could cause improper drying.

If a good finish has been correctly applied, maintenance of the finish will only require a periodic rinsing with water from a garden hose.

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.