Q: The drywalls of our house get covered with moisture, especially when it is cold or rains and we use our unvented gas heaters. Paint store people tell me to use Drylok on the walls to keep out the moisture. There are also drainage problems around the house. Can you help?
A: You might have a dangerous situation in your house. It is quite possible that much of the moisture on your walls doesn’t come from the outside or from drainage problems, although these probably contribute to it, but from the unvented or improperly vented gas appliances you are using.
Extreme condensation on cold interior surfaces is sometimes a sign of poorly vented gas flames. They produce a great deal of moisture along with other combustion products including carbon monoxide, the colorless, odorless gas that can be fatal if enough of it accumulates.
You should stop using the gas heaters, at least temporarily, and ventilate your house thoroughly by opening windows and doors.
Also have all other gas appliances – such as central heater, clothes dryer, water heater and stove – checked to make sure they are properly vented. This should include a check of the chimney to make sure it is not blocked.
If you don’t already have exhaust fans in bathrooms, kitchen and laundry room, you should install them to help carry excessive moisture outside.
Unvented gas heaters should be used only if they are equipped with oxygen-depletion sensors, which shut off the flames if too much oxygen in the space is used, and if there is a working carbon-monoxide detector in the space.
Drylok, a waterproofing paint, is an excellent product but it is designed to seal masonry walls, such as concrete-block basement walls, against moisture seepage from the outside. The drainage problems are best solved by someone who can inspect the site personally.
Q: I have a colored concrete front porch that has some ugly efflorescence stains on it. How can I remove and prevent these?
A: Efflorescence, usually a gray or white powder caused by minerals leaching from the concrete, is especially noticeable and unsightly on colored concrete.
Unfortunately, treatments for efflorescence often involve very strong chemicals, such as muriatic acid, that could permanently mar the colored concrete.
I think the best bet is to use dry brushing, which simply involves brushing off the powdery residue with a stiff brush. You can also use a detergent solution and scrub brush.
The efflorescence should stop eventually, when all the soluble minerals have leached out of the concrete.
Q: Our wood back steps were painted light gray and need painting again. The gray paint shows dirt too easily. What kind of paint should we use and what is a good color for hiding dirt?
A: You should use a “porch and floor” paint, which is designed to withstand foot traffic better than ordinary paints. You can buy one of these paints at any home center or paint store.
Read the directions carefully. You should remove any loose or flaking paint and clean and rinse the surface before repainting. Two coats will look better and hold up longer.
As for the color, any dark color that suits your home décor should work, including dark gray.