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posted: 10/7/2012 5:56 AM

Covering dirt floor will reduce mustiness

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Q. We have an old home with a dirt basement and stone foundation. As part of major energy improvements last year, we had the foundation walls spray-foamed about 3 feet from the top (in other words, about 2 feet below grade), foaming even over the little windows. Now, of course, there is no ventilation, so we have constant moisture/mugginess that permeates into the living spaces, since the only way for it to go is up. When it's nice out, I open the Bilco doors and blow in a fan from the outside, but that's a rare occurrence. We also have a dehumidifier running, but we do not have it going into a drain, so it doesn't do much (if any) good, as the bucket gets emptied only every other day or so.

I'd appreciate any advice on how to improve this situation -- specifically, how to provide ventilation without negating the energy savings we're realizing from the foaming.

A. The key is your dirt floor. As long as it is not thoroughly covered, you will have a problem with mustiness and moisture. A dehumidifier will help only if it is kept running and not allowed to stand by when the tray is not emptied. If emptying it regularly is not feasible, consider draining the dehumidifier into a sump with a submersible pump discharging to the outside, making sure that its outflow will not pool at the foundation and be recycled to the basement.

The dirt floor should be covered with the heaviest plastic you can find. Agricultural stores sell heavy-gauge plastic that resists puncturing when walked on, but a couple layers of 6-mil plastic also will work well if the soil is reasonably smooth.

Make sure the perimeter of the plastic is weighed down with stones or bricks, or bury its edges slightly in a small trench.

You should see a material difference if you do this now and can ventilate the basement as you have been doing during the cool, dry fall days.

Q. Several years ago, you wrote about painting walls plastered directly to outside walls. Our 1817 house has bedrooms like this with painted-over 40-year-old texture paint, plastered directly over the support beams and chimney brick. For some reason (humidity? extremely cold winter? window air conditioner?), it is peeling off now in big pieces, i.e., the old texture paint underneath the newer paint. We can Spackle the cracks but need to know the type of the paint.

A. How long ago was the newer paint applied over the texture paint? If it was painted in the last few years, it may be that the added weight of the new paint was too much for the weak bond of the 40-year-old textured paint, which finally gave up.

If the textured paint surfaces are clean, you can paint them at the same time you paint the patching you plan to do. Any high-quality latex paint should work.

Q. The floors in my house are very cold on my feet in winter. The crawl space dirt floor is covered with heavy plastic. Under the house, the floor is insulated with fiberglass that has a paper covering and is held in place with wires. There are metal vents around the foundation.

What can I do to warm the house floors?

A. If the insulation is not tight against the floor sheathing, there will be some heat loss around the perimeter of the floor. If the insulation is pushed tight against the sheathing, and if the insulation fills the entire depth of the joist cavities, the only improvement I can suggest is to nail 1-inch-thick rigid insulation to the bottom of the joists. This may be difficult to do if the access to the crawl space is not large enough to feed the panels through.

Since the dirt floor is covered with plastic, you should close the foundation vents year-round. They introduce cold air in winter and unwelcome humidity in summer. Otherwise, consider wearing warm slippers.

Q. I want to thank you so much for your detailed reply. I have a roofing contractor coming this weekend to give recommendations. Hopefully, he will provide the same ideas.

I want to make sure he or someone can check the flow of air from our soffit vents through to the roof vents. Is there a technique for doing so, or is it just observation? You clearly identified what could be a big issue for us. Without an attic, the second floor is directly under the large sloped front roof, and the ceilings get warm. Maybe we have no airflow. So glad you thought of that. Thanks again.

A. It may not be possible to determine if you have adequate ventilation in your sloping roof. If you have continuous soffit and ridge vents, there needs to be an uninterrupted air space of at least 1 inches between the bottom of the roof sheathing and the top of the insulation. To determine this may require opening a small area of the roof, and since you are planning on reroofing, it should be easy to do.

If there is no ventilation space, you can add one as I detailed in my earlier answer, or you can simply add 2-inch-thick rigid insulation to the existing roof deck and cover it with synthetic rubber roofing. (That type of roofing needs a soft material cushion to protect it from the wear and tear of thermal movement, so rigid insulation is usually used for that.)

But if there is an air space above the existing insulation, rigid insulation can be applied over the existing ceiling finishes and covered with new drywall.

Q. You have mentioned in the past how to clean a garage floor and prepare it for painting. I misplaced that column and would appreciate your running it again.

A. If your garage floor is stained with oil or plain dirt, sprinkle TSP-PF crystals over the area to be treated and sprinkle hot water over the crystals. Scrub vigorously with a stiff brush on a long handle. Let stand for 30 minutes and rinse.

I do not recall ever recommending painting a garage floor, as it is not likely to stand up to vehicular traffic.

Q. I'm writing to find out why some of my old radiators give out a lot more heat than others. I have my boiler serviced every year, and all the radiators are checked and bled.

What I don't understand is why the radiators that are painted a dark color put out a lot of heat, but those painted silver do not. Is there any connection? Winter is coming, and I'd like to do something about this problem.

A. Radiators painted silver (probably aluminum paint) do not radiate much heat because the paint does not allow heat to radiate. The same applies to any metallic paint.

For maximum efficiency, radiators should be painted with dark colors. Efficient heat transfer diminishes as paint colors get lighter, including white. Black is best but is not too attractive; good results are achieved with brown, green and any other dark color -- the darker, the better.

Q. I have a mold problem in my shower stall. It has become embedded in the grout, especially at the top and bottom. How can I remove this grout, and what should I replace it with? Caulking?

A. The easiest way to remove grout is to use a Dremel tool. You also can buy a grout saw in tile or hardware stores and home centers, but it requires some elbow grease.

It would be best to reapply grout. You may wish to use epoxy grout or, if you use regular grout, to seal it. You can get the needed material in tile stores.

To keep the grout clean, consider scrubbing it every couple of weeks with a mixture of equal parts water and white vinegar, using an old toothbrush.

Q. Should the baffles to be used in a cathedral ceiling to provide an air space above the insulation be taped at the end seams or just overlapped, or should an approximately 1-inch gap end-to-end be left for any moisture to escape into the airflow above the baffle? I read in your book that you did not recommend 16-inch-wide baffles but that 24-inch-wide baffles were OK, which is what my spacing is.

Also, what specific tape can be used on the seams of insulation board, which I plan to install on the bottom of the rafters and on the interior face of the knee walls -- maybe foil tape for heating ducts or Tyvek tape? Our Home Depot says it doesn't sell any.

A. There is no need to tape, overlap or leave a space between the ventilation baffles. You can use Tyvek or similar tape to tape the joints of the rigid insulation you plan to install. This will be your vapor retarder.

The reason I do not recommend 16-inch-wide baffles is that they are flimsy and easily collapse under the pressure of expanding fiberglass insulation. They also allow only a few inches of ventilation. The baffles for 24-inch framing have a reinforcing leg in the center and offer wider spaces for ventilation.

Q. I read your column weekly, and I wonder if the questions and answers have been published in book form. If so, please advise how I can get a copy of this material.

A. Yes, 30-plus years of selected questions and answers have been published in a book by Upper Access Inc. "About the House With Henri de Marne" has more than 400 pages and can be purchased through Upper Access Inc., (800) 310-8320,, or in bookstores.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. Write to him in care of the Daily Herald, P.O. Box 280, Arlington Heights, IL 60006, or via email at His book, "About the House," is available at and in bookstores.

2012, United Feature Syndicate Inc.

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