Q Our outside deck, built of random granite slabs which were laid in mortar over prestressed concrete planks, leaks to the room below. We've been advised to apply a sealer, but so far four coats have failed to significantly stop the leaks. Besides, the coating makes the surface slippery under snow. What advice do you have to halt the leaks? J.B. Stull Hampstead, N.H.
If four applications of a sealer have failed to plug the leaks, there may be a structural problem at the mortar joints. Look for cracks, even hairline, in the mortar as well as between the mortar and granite slabs.
Partial removal and repointing of the mortar joints may be required, assuming the leaks occur at the mortar joints.
Remember, sealers can only stop leaks where porosity is present. Granite is far less porous than the joints.
When the mortar joints are made tight, apply a coat or two of Tuff Stuff, or equal, to the surface. Tuff Stuff does not present a slippery surface.
Tuff Stuff is made by Sealwall Products Inc., 36300 Lakeland Boulevard, Eastlake, Ohio 44094. Tony Baxter of Sealwall writes: ''You could coat the bottom side of the concrete roof deck over the room with Sealwall. I am sure it will stop the water.''
Ask the manufacturer of the sealer now on the granite what to use to remove it down to the raw granite, if necessary.
Q How can I remove old caulking from the window sills of my house? Frances J. Fischman Cincinnati, Ohio
To remove caulking from window frames and sills, first try a product such as Toluene, a solvent found in most caulking compounds. Use care in its use since it has a low flash point.
Toluene may be injurious to oil-base and certain other types of paint. Thus, run a test on a small area first and observe the results.
If Toluene proves unsatisfactory in removing any unwanted caulking, use a product such as Sure Klean Asphalt and Tar Remover, made by ProSoCo Inc., PO Box 1578, Kansas City, Kan. 66117, or equal. Follow the instructions on the label. Your local paint or supply store should market the product.
Q Our kitchen walnut panels are scummy from stove vapors. Is there an inexpensive household cleaner we can use? Leonard Keppler Newport Beach, Calif.
Our consultant on such questions suggests a soap called Oil of Murphy. He says it mixes with water, is made especially for furniture and cabinets, is less expensive than some commercial cleaners, and is very effective.
If you have a question on designing, improving, or maintaining your home, send it to the real estate editor, The Christian Science Monitor, One Norway Street, Boston, Mass. 02115. Forrest M. Holly is a longtime California builder now living in southern Arizona.m