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Q A masonry chimney vents an oil furnace in our house. After replacing the old converted coal furnace with a new superefficient model, we observed seepage throughout the chimney walls which freezes during cold weather. We had the flue professionally cleaned last fall. What is at fault and what can we do to prevent the seepage?
S. Prochazka Ballston Lake, N.Y.
The source of the seepage is likely a faulty chimney cap. The cap area is the most common source of chimney leakage. Apparently the cooler temperature of the new oil burner does not dry out the seepage, which was removed by the old, hotter furnace.
To halt the seepage:
* Carefully caulk and seal the crack between the top flue liner and the adjacent concrete cap.
* If the cap has a positive drainage but is cracked, carefully fill the cracks to ensure that no water migrates through it. If the cap has a negative pitch or is too badly cracked to be repaired, remove and replace it with a new sloping concrete cap.
* Install a metal hood, as described in Technical Notes 19, Revised, April 1980, by the Brick Institute of America, 1750 Old Meadow Road, McLean, Va. 22102 . You can phone the institute at: (703) 893-4010.
Q In our new home the outside concrete slab is unconnected to its adjacent inside floor slab. When the ground freezes, the outside slab rises about three inches. What can we do short of tearing out the slab and pouring a new one over a gravel bed? I assume the raised slab drops when the ground thaws.
A reader Iowa City, Iowa
If you can put up with it, wait for the spring thaw to see if indeed the slab retreats those three inches. If it does not, then replacing it over a gravel base is the best remedy. You should also slope the base to force positive drainage away from the slab and dwelling.
Keep rain or ground water from seeping under the slab as well by sloping the slab surface away from the building.
If the slab does drop down the three inches and if the surface has drainage away from the building, excavate a 12-by-12-inch trench around the three-sided perimeter. Slope the bottom to drain away, and fill with gravel. Provide an escape for surface or ground water to ''daylight.'' The idea here is to forestall water from migrating to, or standing below, the old slab.
Replacing an 84-square-foot exterior concrete slab is not a major project and may be the final solution.
To the real estate editor:
In answer to the question on making cotton cloth covers for radiators, why not buy wicker or rattan trays which may be either circular or square in shape? The trays have ''spaces'' to let all the heat into the room.
You can buy them at department, wicker, or Oriental stores. I've bought six so far - up to 32 inches round and 27 inches square. They look very attractive and do the trick. Just rest them on the radiator below the windowsill.
Occasionally I soak them in the bathtub, which keeps them from drying out.
Painting unsightly radiators still does not hide them.
-- Edna S. Stegmuller