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How to eliminate musty drain odors

Q. What can be the problem when all the drains in a house smell musty? Is there any treatment that can be performed?

DAVID NOCELLA

A. Is it a musty smell or sewer gas? If you smell a noxious sewer-like odor inside your home, chances are it is sewer gas escaping from the drain system. Sewer gas not only smells gross, the methane and bacteria it contains can be dangerous to your health, causing headaches.

Your house drains have traps in the pipes that hold a certain level of water to seal out methane gas. Oftentimes a rarely used drain will dry out and allow sewer gas to enter the home — it’s called a “dry trap.” The fix here is to run the water in these drains once a month to ensure water in the trap seals out the gas.

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If it’s simply a musty smell as you indicate, it could be bacteria growing in your drain. Try cleaning it with this tried-and-true vinegar and baking soda mixture:

1. Mix one cup of white vinegar into the drain.

2. Follow with one cup of baking soda.

3. Let that sit for two hours.

4. Pour one gallon of boiling water in the drain.

5. Wait 10 minutes and flush with cold water for 10 minutes.

6. SAFETY NOTE: Never, ever mix vinegar and chlorine bleach. Remember your chemistry lessons. It will create a toxic gas!

Q. I installed medium-density fiberboard (MDF) crown molding in my dining room. Every winter the joints gap, and every summer there is a ridge from the caulking. I suspect this is due to humidity. Any suggestions to minimize the problem, short of replacing with real wood trim?

GRTAYLOR1977

A. Seasonal changes in humidity cause trim and flooring to shrink in the winter and expand in the summer. The moisture content of wood is tied directly to the relative humidity of the surrounding air. The higher the relative humidity, the higher the moisture content of the wood. MDF is a high-grade composite material that performs better than solid wood in many areas. Made from recycled-wood fibers and resin, MDF is machine-dried and pressed to produce dense, stable sheets. I hate working with it, but it is more stable than solid wood and stands up better to changes in heat and humidity.

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Back priming and sealing your end grain would have helped, but the only way to avoid this is to condition the air and control the humidity in your home year round.

Q. I have several lamps that carry a label that says “Do not exceed a 60-watt bulb” from the incandescent period. Does this same warning apply to the new energy-saving compact fluorescent light bulbs? These new bulbs are labeled 13 watts, but are the equivalent to the old 60-watt incandescent bulbs. I would like to put a 75- or 100-watt-equivalent CFL bulb in some of these lamps. Would this cause problems?

ART BORMAN, Framingham

A. The wattage rating is designed to prevent the wiring in the area around the fixture from overheating and causing a fire. You can use compact fluorescent that produces more light as long as you do not exceed the fixture’s wattage recommendation.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @globeaddress or @robertrobillard.