HARRY WOLF, Winchester

A. I'll bet it was your wife who noticed something fishy. Wives, in my experience, have a better eye then men, and can spot a 1/4-inch slope in 6 feet more quickly than men. Or at least they will not tolerate it, and point it out to the beleaguered do-it-yourselfer. And believe me, a 1/4-inch drop in 6 feet is a mighty shallow slope. Anyway, leave things as they are. It is much better to have the mantel level and the sides plumb (vertical) than to try to follow the off-level ceiling and floor. To do so would create many, many more problems.

A good example of why one should keep things like mantels level, ignoring the contours of the room, is the rule in wallpapering: Each strip of paper should be plumb. Period. Ignore a sloping ceiling, canted floor, and off-plumb corners.

Just think of how a vertical stripe or horizontal stripe pattern would look if you allowed it to follow the slope of the ceiling. It's chilling to even think of it.

One thing you might try if push comes to shove and you have to do something about it: Install a trim along the wall at the ceiling, tapered slightly so that the bottom of the trim is level. Then everyone will be happy. The handyman has done that in his house of many levels (and off-levels), and while it only fools the eye, it does, indeed, work.

Q. I need an objective opinion. The varnish came off a gumwood mantel over the fireplace opening, I presume from the heat of the fire. Then I discovered a 1-inch gap between the mantel and the brick front. A chimney sweep suggested filling that gap. Another said the fireplace needs rebuilding. I got six different opinions as to what to do, but all agree that I was lucky that there was no house fire. What should I do?

A.R., Somerville

A. A mantel is set against the brick front of the fireplace or directly on the wall around the brick front, so a gap can easily occur, just above the fireplace opening. Heat might have gotten in that gap to hasten the failure of the varnish, but that could happen over the years even without the gap, because there is some pretty high heat rising out of the firebox opening. That heat getting in the gap could be a hazard, because when wood is heated repeatedly and allowed to cool off, its combustion temperature gets lower. Wood will ignite at 500 degrees, and if that combustion point is lowered, the hazard is greater.

I doubt that the wood will get that hot. Even if it is too hot to touch, it might be only 120 to 150 degrees.

At any rate, you could fill that gap with pine or gumwood to match the original. This filler wood will get as hot as the adjacent mantel, but it would also stop the heat from getting between mantel and brick or wall.

One more thing. The mantel may be too close to the firebox opening, causing the wood to heat. The cure there is to replace the mantel, if possible, with one whose ``header'' (the horizontal top of the mantel) is higher up from the top of the firebox opening.

Q. I need an objective opinion. The varnish came off a gumwood mantel over the fireplace opening, I presume from the heat of the fire. Then I discovered a 1-inch gap between the mantel and the brick front. A chimney sweep suggested filling that gap. Another said the fireplace needs rebuilding. I got six different opinions as to what to do, but all agree that I was lucky that there was no house fire. So what should I do?

A.R., Somerville

A. A mantel is set against the brick front of the fireplace or directly on the wall around the brick front, so a gap can easily occur, just above the fireplace opening. Heat might have gotten in that gap to hasten the failure of the varnish, but that could happen over the years even without the gap, because there is some pretty high heat rising out of the firebox opening. That heat getting in the gap could be a hazard, because when wood is heated repeatedly and allowed to cool off, its combustion temperature gets lower. Wood will ignite at 500 degrees, and if that combustion point is lowered, the hazard is greater.

I doubt that the wood will get that hot. Even if it is too hot to touch, it might be only 120 to 150 degrees.

At any rate, you could fill that gap with pine or gumwood to match the original. This filler wood will get as hot as the adjacent mantel, but it would also stop the heat from getting between mantel and brick or wall.

One more thing. The mantel may be too close to the firebox opening, causing the heating of the wood. The cure there is to replace the mantel with one whose ``header'' (the horizontal top of the mantel) is higher up from the top of the firebox opening.

The bottom line on this is to make sure the fireplace is in good shape, without broken brick, broken flue liner (if any), or any other damage.

Q. When I cleaned up a white marble mantel with soap and water, it continued to smell like heating oil. How can I get rid of that odor?

GEORGE PERESMAN, Newburyport

A. Marble is absorbent, so you must use an absorbent material to pull out the oil, and you must use a solvent to activate the oil in the marble. So, dampen the marble with paint thinner, and sprinkle baking soda over it, at least half an inch thick. Let it sit for an hour (you may see the baking soda turn yellow, which means it is absorbing the oil). Sweep it up and throw it away. Repeat as necessary.

Repetition is the secret to success. And rest assured it will work. The handyman spilled some diesel oil in the trunk of his car years ago during the energy crisis. But he wiped up as much as he could, then gave everything the baking soda treatment. Eventually, every trace of oil -- and odor -- was gone. Other absorbents you can use are Speedy Dry and cat litter. Both are absorbent clays.

Q. I put up a limestone mantel over my fireplace, and it looks very nice. Is there anything I should seal it with to help keep it clean and possibly prevent efflorescence, the leaching of lime out of the mantel by water? After all, it is limestone. And, by the way, should I seal outdoor concrete?

CRAIG LEPPANEN, Windham, N.H.

A. Try a clear sealer; I think a clear masonry sealer will be best to make the limestone water-resistant, resistant to stains, and more easily washed. I don't think the sealer will prevent efflorescence, which is pretty hard to avoid. But I don't think that will be a problem because the mantel is indoors and is unlikely to take up much moisture, which is what causes efflorescence. As for sealing outdoor concrete, I don't think there is any need, despite the TV propaganda from manufacturers of sealers.