Q: My flagstone hearth has many grease stains. How can I clean it and what can I use to seal the surface so it won't get dirty again?

A: Although you can scrub the hearth with any strong household detergent, flagstone is very porous and the stains may have soaked in too deep to get them out easily. I think your best bet is to try to liquid driveway cleaner. After using this, apply a clear stone sealer (sold in hardware and household stores, as well as by stone dealers). This will darken the stone and give it a kind of wet look, but it will keep stains from pentrating easily.

Q: My house is very humid on the inside most of the time, I had trouble with the windows sweating a lot early this spring (new windows were installed a few months before). I bought a hygrometer and found that the relative humidity inside during May was consistently 70 to 80 percent. The window installer said that was why the windows were sweating. Do you have any idea how this can be corrected?

A: Most of the time your house is producing more moisture on the inside then can escape when the windows are closed. There may be a number of reasons for this:

1. You may need an exhaust fan in the kitchen to dispel moisture vapor while cooking or washing.

2. You may need an exhaust fan in the laundry room for the same reason.

3. If you have a clothes dryer, make sure it is vented directly to the outside.

4. If your basement has crawl space, make sure the dirt floor is covered or paved.

5. If you have hot-air heat with a humidifier, make sure the setting is not too high -- or try disconnecting it entirely.

Q: My house has insulation on the attic floor, and the attic is ventilated by small vents under the eaves only. I also have a crawl space under the house that is sealed against rats. My problem is that the whole house is very damp due to condensation; the eaves show signs of mold, and there is a musty odor in many places. What can I do to correct this?

A: You need a lot more ventilation in the attic, with additional vents either up near the peak or along the ridge. There should be at least one square foot of free opening for every 300 square feet of attic floor area. You also need ventilation in your crawl space. The dirt or soil should be covered with heavy polyethylene that is overlapped where sheets meet. Vents should them be installed on opposite ends or sides of the crawl space to ensure cross ventilation. The vents should be large enough to provide about one square foot of free opening for every 600 square feet of floor area (assuming the floor is covered as described above, or paved with concrete).