Q. We recently had a new concrete patio installed in our yard and now it has rust stains from a metal lawn chair that got wet when a sprinkler was turned on. How can we remove these ugly stains?

A: Rust stains are hard to remove from concrete, but they can often be bleached out with oxalic acid. This bleach comes in crystal form and can be found in paint and hardware stores. Mix a saturated solution of this with hot water (keep mixing the crystals in until no more will dissolve), then mop this on over the stained areas and let it dry. Rinse with plain water. If the stains are not completely removed, another application may be needed.

If you can not bleach the stains out, you may be able to get them out with a commerical rust-removing liquid or jell. Apply this liberally, let soak, then rinse off according to the directions on the package.

Q: we recently bought a used mahogany drop-leaf table. Apparently one leaf had been exposed to sunlight for a number of years, while the other had not. That leaf has a bleached look and the grain is blonder, but the finish seems undisturbed. The other leaf and the top are much darker. What do you suggest to get all the surfaces the same, or near-same, color?

A: The only way you can get all the wood back to the same color, is to strip all the existing finish off, down to the bare wood. You can do this by sanding, but I think that using a chemical paint remover will be easier and faster. After the wood is cleaned off, see if the parts are still different in color. If they are, you have three options to get them the same shade:

1. You can bleach the darker section with wood bleach; 2. You can try to stain just the light sections to darken them to match the darker sections; 3. You can stain the entire table with a fairly dark stain, applying more to the lighter leaf and less to the darker ones.

The third option is the easiest, but it may take some experimentation to get a good blend. Bleaching is tricky in some cases, and requires a stain when you are done. Experiment first on the underside to see how the wood takes the stain.

Q: My dog urinated on my parquet wood floor and someone cleaned it off with water. Now there is a large white stain in the finish. Can you tell me how this can be repaired?

A: Your floor was apparently finished with shellac, which turns white when water is used on it. First, try rubbing lightly with a piece of very fine (00) steel wool that has been dipped into a liquid floor wax. If this doesn't get the white stain out, rub with fine steel wool that has been dipped in denatured alcohol. This solvent for shellac will take the finish off, but if work carefully you may be able to get some of the finish off without taking it all off down to the wood. If the stain has penetrated all the way through the finish you will have to get it all off and apply fresh shellac.

Q: I recently moved into an old house where one of the living room walls was covered with Sanitas (a fabric-type wall coverning). I do not like the pattern, but am hesitant to take the material off because I do not know the condition of the wall behind it. Can this material be painted over and, if so, would a latex or an oil paint be better?

A: You can paint over this quite easily, but first you must scrub the surface clean. Either type paint can be used, but I favor latex paint. If you don't want the seams to show through the paint, you will have to use spackling compound to fill them in and smooth them over. Also, make sure the material is still sticking tightly on the wall, otherwise the paint may cause it to peel off.

Q: My apartment walls are quite dirty in many places, especially in the kitchen and bathroom, and over some of the windows. In getting estimates from painters to redo all these walls, the matter of washing first came up. One of them told me there is an alcohol-based product that can be applied over the dirt and grease without bothering to wash the walls down first. Have you heard of this, and will it work?

A: I have heard of this type sealer, and have mentioned it on numerous occasions in this column. There are at least two brands sold nationally: One is Enamelac, and the other is BIN. Both are alcohol-thinned, and both will cover grease and dirt to a great extent. But I think you should wash off at least the worst of the dirt and grease first.