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handyman on call

Water vapor to blame for black marks on wall

Q. The inside of my exterior walls are showing strange, thin horizontal black marks that seem to be between the wood lath inside the plaster, which are wider than the black marks, but only on the second floor of a three-story clapboard sided Federal house that is 200 years old. The walls are not insulated. What is this phenomenon and how can I stop it?

KATHY, NEWBURYPORT

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A. It happens in any season. I call it mold stripes: Water vapor (moisture) builds up in the house until it condenses into water on the wall. You can’t see it but it’s there. The wood lath (1½ inches wide) makes the wall a little warmer, so the water vapor condenses on the wall between the lath, (maybe 1/2 inch). When this happens, black mold will grow. A temporary fix is to clean the walls with a solution of 1 part bleach and 3 parts water. Wear skin and eye protection when working with bleach. I think other antimold treatments are not very good.

 A permanent cure is to blow cellulose insulation in all walls. Why are the black stripes showing only on the second floor? One reason is that moisture rises, leaving the first floor unaffected. Why the third floor is unaffected beats me, except perhaps the third-story walls are insulated. Also, the moisture was all used up on the second floor, so there was none left on the third. Or, perhaps, there were no mold spores on the third-floor space.

Q. I recently purchased a used armoire that has imprint stains from where gel stickers were placed. Is there a product or method I can use to remove the residue? I have tried using Goo Gone without success.

RUTH BROGAN, BY E-MAIL

A. Yes, there is: Rub the stains with Mr. Clean Magic Eraser.

Q. The railings on my back porch are made of 1½-inch aluminum pipes which I would like to paint. Or should I leave them shiny?

ROBERT BLOUIN, WEST NEWTON

A. I Googled “painting aluminum” and came up with many ads by people who want to do the work for you, and conflicting accounts over oil vs. latex. Big help. So I fell back on my own tried and true method of painting aluminum. Sand the aluminum lightly to roughen the finish, and apply two coats of an exterior latex solid color stain.

I think black is nice, but if you want to keep them shiny and bright, just leave them alone for a while. When they age, then you can paint.

Q. Is it a good idea to close central air-conditioning vents in unused rooms? We have a guest room, little-used bathroom, and small laundry room where we keep the vents shut to save on electricity. What is your recommendation?

SALEM, N.H.

A. Shut the vents and the doors, and you will be saving a little electricity, worth the simple efforts. Doors and vents will be easy to reopen when necessary. It makes sense. Some critics may say it unbalances the system, but I think a well-designed system can improve with some outlets shut off. If a system’s balance can be affected by closing off some outlets, why do they make the outlets capable of being opened and closed? By the way, concerning that little-used bathroom, make it habit to flush the toilet and run all taps for a while to refill the traps. Water can evaporate in an unused bathroom until it allows sewer gases to go into that room.

Q. Two years ago when my kitchen disposal backed up the plumber told me that the whole line was backed up with vegetable matter. He snaked the drain, power flushed the whole line, and replaced the disposal. Now, two years later he had to come back and flush again for the same reason. He tells me to use the disposal only for the small stuff that drops in the sink and put most of the vegetable garbage in the trash can. Huh? I’ve been using garbage disposals for 40 years. Why is this happening now?

EL, IN WEST ROXBURY

A. He installed a brand new disposal? That should have fixed every thing. I don’t know what to say except that the disposal, not the plumbing is defective. Originally, it sounds as if the disposal blades had gotten dull, and the blades or whole disposal may need replacing. You are right, the plumber’s idea to go easy with the solids defeats the purpose of the disposal.

Peter Hotton is also in the g section on Thursdays. He is available 1-6 p.m. Tuesdays to answer questions on house repair. Call 617-929-2930. Hotton (photton@globe.com) also chats online 2-3 p.m. Thursdays on www.Boston.com.
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