Q. The blasted-out basement in our 30-year-old house has had occasional water seepage for the past nine years. We are told the water table has risen. The concrete-floor surface is cracked, dusting, and grainy. What can we do? J.K. Rose New Haven, Conn.
A. Since the basement is built on rock, the seepage problem may be a rising water table, not settlement.
Short of tiling the exterior foundation perimeter below grade to draw the seepage to ''daylight,'' here are three suggestions:
* Fill the floor cracks in the slab with hydraulic cement broomed over the surface.
* Stop the floor from dusting and seal out the moisture by applying a sodium-silicate solution that will react with the alkali in the concrete and harden it. This solution will make the slab more dense and thus hopefully inhibit water penetration from below. Two or three coats are suggested. Among others, Sealwall's Curecon (formerly called Sealit) will serve well as a floor hardener.
* To waterproof the basement walls, apply a cementitious coating, such as Sealwall. Follow the manufacturer's directions to the letter. Sealwall Products Inc., is located at 36300 Lakeland Boulevard, Eastlake, Ohio 44094. The phone number is: (216) 951-3445.