Heavy rains and accumulations of melted snow in many parts of the country during recent months have caused dampness and flooding in a great many basements.

The first thing the homeowner should do is make certain there is adequate drainage of surface water near the house. The more water that soaks into the ground, the greater the hydrostatic pressure that will build up in the subsoil to force water in through small cracks or porous sections in the masonry.

That is why most houses need a well-designed and properly maintained roof drainage system of gutters and leaders to carry away the large amount of water that pours off the roofs during a heavy storm. If gutters are clogged or leak badly they will allow water to pour down along house walls. This water then soaks into the ground next to the foundation to add to the pressure.

Even gutters that work properly will not help much if the lower end of the leader, merely empties onto the ground nearby. Water should be directed into splash pans or into underground pipes that will carry it several feet away from the foundation before dispersing it. Better yet is an underground dry well located at least 10 feet away, or a sloping drain pipe that carries rain water to a sump or other safe drainage point.

To further help drainage of surface water, the ground on all sides should slope away from the house foundation, never toward it. In addition, below-ground basement window wells should drain quickly so that water does not build up to a point where the well fills up and allows water to flow in under and around the window frame.

After all preventive measures have been taken from the outside (short of digging down down to the footings and applying a waterproof membrane coating to the outside of the foundation walls), there are patching materials and coatings that can be applied on the inside that will help all but the most serious leakage problems.

The first step is to seal and patch all cracks or holes that allow water to enter. Very fine cracks along the joints where walls meet floors, or in the walls and floors themselves, can be effectively sealed in most cases with one of the two-part epoxy sealers that are brushed on with an ordinary paint brush. These sealers also work well on porous sections where seepage is slight. They must be applied when the surface is clean and dry, and work best if all old paint is removed first by wire brushing or scraping.

Larger cracks along the floor-to-wall joint, or in other parts of the masonry where shrinking or setting may have been the cause, are best filled with one of the quick-drying hydraulic patching cements (Waterplug, Fastplug, Quickplug, or Aquaplug).These are powdered patching materials that are mixed with water and expand as they set, so that they lock firmly into cracks or openings to make up for previous shrinkage.

This characteristic, coupled with the fact that they dry quickly, makes it possible to use these cements for filling cracks and holes even while water is still actively flowing through them.

To do this, mix a small batch according to directions on the container, then hold this in your hand until it gets warm and starts to stiffen slightly (about three minutes). Then pack tightly into the crack with your hand or with a small trowel and hold in position until it stiffens.

Many leaks occur along the joint where wall meets floor, so this joint often needs special attention. Before filling this or any other crack with hydraulic cement, the crack should be cut out with a hammer and cold chisel so that a square, or slightly undercut, groove is created. It should not be a V-groove, because this provides a poor mechanical bond or key for the cement to hold in. Brush out loose duct and dirt, then pack the cement in, a section at a time.

After all the cracks and holes have been patched, either with hydraulic cement or with a vinyl concrete patching cement (this works well in smaller cracks where water is not actively flowing or seeping), the next step is to coat the walls themselves (assuming that merely patching cracks does not do the trick). There are various water-proofing coatings for this purpose on the market. Some are powders that are mixed with water, others are ready mixed.

Some companies make more than one type - a so-called regular-duty coating, and a heavy-duty version.Where there is a choice, use the heavy duty - it is much better at holding back water.

Also, some companies sell additives (liquid) that can be mixed in to increase holding power, and wherever this is available it's a good idea to buy it and mix it in according to the directions on the package. The two-part epoxy sealers mentioned earlier can also be used to coat walls but their high cost makes them impractical for large areas; they are most often used to seal the floor-to-wall joints, or to seal small, porous areas.