There is dampness in my basement between the walls and the floor. The basement is unfinished. How do I find a reliable outfit to review my problem and give me advice that I can trust? What questions do I have to ask?

The short answer is to call the Long Island chapter of the National Association of the Remodeling Industry. They can offer guidance and refer licensed and insured members (631-673-6274; nari.org). Before hiring a contractor, you also can check with the Better Business Bureau (bbb.org) to see if there are any complaints against the company.

THE CULPRIT

There are several. One is created by the eventual breakdown of tar - a damp-proofing material - applied around a home's foundation. As tar breaks down, water can get in. "One of the most common entries of water in the basement foundation is located where the floor and the wall meet," says Bill Simone, owner of Healthy Basement Systems in Islip Terrace. "We call this seam a 'cove.' As the water table rises and rainwater settles, the water will rise higher and higher, creating an enormous pressure onto the cove area."

Gravity is another culprit. Sandy Beach, a home builder based in Hampton Bays, says the first thing to look at is the land grade. "If you look to the side and to the back of your property and it's higher than your yard, where is the water going?"

DRYING OUT

A minor amount of water can be sucked up by a wet/dry vacuum. Major accumulation needs a major pump - and professionals. Air helps in the drying process. "Open the windows and use fans to move the air around," advises Beach. Regardless, every basement on Long Island should have a dehumidifier, Simone says.

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ASSESSING THE DAMAGE

Mold needs the right conditions to grow, says Simone. "In cooler weather, it grows slower." Surface mold can be fixed with ammonia, he adds. But if you have a finished basement with drywall and it's damaged with more than six inches of water, it should be ripped out, Beach says.

PREVENTION

Companies offer various solutions and products. French drain systems are one option. Here, a trench captures groundwater and diverts it.

An electric sump pump will keep water out, but not during a power outage. Maintain your window wells - they should be debris-free and backfilled with stone for drainage, says Beach. As for changing the grade of the land, a qualified landscaper can do the job.