Q. I have removed the ceramic tile floor from my bathroom, but a lot of gray mortar is left on the plywood, and in some cases the tile took some of the plywood (a full ply) with it as I removed it. How can I get that mortar off? And should I fill those chipped plywood gaps or will the new tile span the depressions?
JOHN CASHMAN, Dedham
A. You can chip off the mortar with a cold chisel and hammer. Or, use a wood chisel, which might be easier to work with even if it is not the right tool to use. To remove residue, sand it. To fill those gaps (and you should), use a leveling compound, a plaster-like material easily troweled into the gaps and smoothed off. Apply the new tiles with a thin-set mortar.
Q. We are thinking of putting in central air conditioning in our 70-year-old Tudor. We have casement windows so cannot easily use window units and we don't like the idea of cutting through the walls. We have hot water heat so we will have to install ductwork as well as the a/c units. What is best to use: conventional ductwork or the new high-velocity ducts? One contractor who does the conventional installations said the high-velocity ducts are noisy. What do you think?
JOHN DOOLEY, Reading
A. I think the contractor who said the high-velocity ducts were noisy did you and himself no favors. I think the high-velocity ducts are the way to go. Even though the system may be more expensive, it is not noisy. I have stood directly under a high-speed vent and found it not only quiet but I could not even feel a breeze.
Q. How often should I have my chimney swept? I have a fire in my fireplace six days out of seven in cold weather.
NICE 'n' WARM
A. With that much use, once a year is important. If the fireplace is used occasionally, then once every two years should be adequate.
Q. An addition over a crawl space, a large family room, has been odor-free for 40 years, but now it has a mold odor. I know that there are certain things that have to be done, but I don't quite understand why it is occurring after 40 years, especially during the summer drought. I had a company assess the situation, and it suggested putting a pool liner type covering on the earthen floor of the addition, sealing the crawl space completely, and installing a dehumidifier, at a considerable cost. The company insisted that closing the crawl space would work. What do you think?
HERTZ HENKOFF, Needham
A. It's all a matter of reducing humidity (water vapor) in the crawl space and in the family room to end that moldy smell. Many new houses are virtually air tight, which help keeps them dry, but that can result in stale air and numerous other pollutants.
In my experience, venting a crawl space in the warm season is still the way to go. A proper sealing can be quite expensive. A barrier on the earthen floor is a good idea, but I say install as many vents as practicable; you really must allow all that water vapor to escape. Also, a dehumidifier is expensive to operate, and ventilation is free. Make sure the crawl space ceiling is insulated with fiberglass with a paper backing, to prevent water vapor from coming up into the family room.
Why it occurred after 40 years of no odor, beats the heck out of the handyman.
Q. We are restoring our old fireplace, and are wondering if painting the inside of the firebox would be a good idea. One man suggested using a HHR (high-heat-resistant) spray paint, but that protects only up to 1,200 degrees, and I think a fireplace fire can get hotter than that. The firebox looks as if it is lined with a yellow brick of some kind.
A. That yellow brick is fire brick, and you are right; a fireplace fire can get hotter than a mere 1,200 degrees. And when it does, it is likely to peel the paint, making a bigger mess than you have now. A firebox is not designed to be painted, and therefore shouldn't be.
Q. I am having a new roof put on my place in Vermont, and the roofer said it might be a good idea to avoid monotonous uniformity, and suggested using a multi- colored shingle. I like a solid color, without a pattern, but I am concerned that even a one-color shingle will have too many variations.
A. Shingle colors can vary slightly from lot to lot, so I suggest that you ask the roofer to buy all shingles from the same lot. If that cannot be done, use shingles from one lot on one side of the roof and those from another lot on the other side. As for aesthetics, choose black. Black will have no effect on keeping cool in northern climes. White and light pastels are best in the South.
Q. I have hot water baseboard heat, and now I am getting soot and dark marks on walls and ceilings, especially above the baseboard heaters. What is causing these marks and what can I do about them? My wife does light scented candles occasionally.
T.R. JEROME, Holliston
A. There are a lot of reasons. The heaters are distributing dust particles that collect on the wall. Sometimes the heat is too high, and the particles carbonize. There may be many other reasons, but the best way to tackle the problem is to keep the burner clean and properly adjusted, and make sure the boiler is working properly and at the right temperature. And, keep the fins and other parts of the baseboard units clean, and be careful not to bend the fins.
And finally, cool those candles; aromatic candles contain oils that create a lot of soot.
The handyman got this info from John P. Certruse of North Attleborough, an engineer whose company specializes in diagnosing causes of various stains and offering solutions. The company is Industrial Services & Engineering in Attleboro. Thanks again, John.
The Handyman on Call also appears in the Sunday Real Estate Section. Peter Hotton is available from 1 to 6 p.m. Tuesdays to answer questions on house repair. Call 617-929-2930. Hotton also chats on line about house matters from 2 to 3 p.m. Thursdays. Go to Boston.com. Hotton's e-mail is email@example.com