Peeling wallpaper; time for new furnace?

Q. Three sheets of wallpaper in one of my rooms are peeling from the top down. They are 14 years old and are on real plaster, and it is in good shape. I was advised to use an adhesive called Roman Pro-525 Border, used for hanging border paper on paper. Will that work?

CHARLES MacDONALD, West Newton

A. Sure, anything will work. If the paper is peeling (after 14 years!), not enough paste was used, and possibly the walls were not sized prior to hanging, or it simply dried out. I think any kind of vinyl paste will work, with or without the size. Be sure to wet the paper as well as the wall with the paste.

Q. How do you tell when you need a new furnace? Mine is gas (hot air, that is), and 38 years old. Sometimes I see black smoke coming from the chimney.

CURIOUS

A. The black smoke may be because of a maladjusted gas flame, which of course should be blue and not yellow, and can be adjusted. What else to check for? No heat. Low efficiency: Generally anything below 70 percent is low efficiency, and that counts for both the burner and the heating unit (furnace or boiler). Also, a burned oil or gas smell coming through the vents, which indicates a cracked heat exchanger and is hazardous to your health; hot-air heaters are prone to this. So, aside from smelling fumes, inefficiency is the best reason to replace a furnace. New burners, furnaces, and boilers can be considerably more efficient than a unit that is 20 years old or more. After all, with rising fuel prices, it will pay dividends to replace an old unit. Since yours is 38 years old, a new one will be much more efficient.

Q. My home is like a deck house that had a tar and gravel roof that is almost, but not quite, flat. The roof leaked so I put on a rubber one, which is OK except that when ice builds up on it, it is steep enough to allow a lot of ice to fall off with one heck of a swoosh, imperiling anyone under it. How can I prevent that?

SLIPPERY ROOF

A. You can have a roofer apply snow hooks, a fancy name for a snow and ice fence that will hold everything in place until it melts. If your roofer cannot find such things, write or call: Vermont Slate & Copper Services Inc., P.O. Box 430, Stowe, VT 05672, 802-888-8573 or 888-766-4273; or M.J. Mullane Co., 17 Mason St., P.O. Box 108, Hudson, MA 01749, 978-568-0597.

Q. My finished basement has a ceramic tile floor, and I am plagued by spiders. How can I keep them away? I keep sweeping them down but they always come back. Also, how can I repoint a bluestone block patio? The blocks are set in sand, and are mortared in the 1/4-inch gaps between them.

KARINA MELEK, Lexington

A. Keep sweeping the spiders down because that is the only thing you can do. They will be back, as you have discovered. Be happy with this. The spiders are there for dinner, eating any kind of bug they can find. If the bugs were not there, the spiders would go away or maybe eat each other.

As for the bluestone blocks, forget about remortaring (repointing) them. Because they are in sand, they move when stepped on, and will heave in winter, tending to break up the mortar in a year or so. So, instead of remortaring, dig out the old mortar and sweep in stone dust, then water it. When the stone dust settles, add more, and water it, until you cannot add anymore. It will get nearly as hard as mortar but will be flexible enough to move with the blocks and last a lot longer.

Q. I am getting a lot of condensation in my bathroom. I discovered that the bath vent that goes into the ceiling is vented to the soffits (the roof overhang), but it simply is dropped into the soffit. They must have thought the 2-inch diameter vents would allow good air flow. How can I fix that?

Also, I plan to have my 1987 house repainted. A lot of the clapboard nails have rusted, making some pretty ugly marks. The painter suggested putting a dab of caulking on the nail heads before painting. Will that work?

ROBERT HANSEN, Pepperell

A. Throwing the vent willy-nilly simply will not work. It is easily fixed: Cut a hole in the soffit so that the vent fits snugly into it. The moist air will bypass everything and go outside, where it belongs. Those 2-inch diameter vents are useless. The proper soffit vent is a 2-inch wide continuous strip.

Regarding caulking nail heads, in a word, no, it will not work. Even indenting the nails will not work because the clapboards are too thin, and countersinking them may drive the nails all the way through the clapboards. The wrong nails were used, and replacing them with stainless steel nails is the only thing that will work. To do that, pry up the clapboard and tap it back in place, revealing the old nails. Pull them out and drive a stainless steel nail into the same hole. If the hole is too big for the nail, then nail 1/2 or 3/4 of an inch away from the hole. Fill the empty holes with a glazing compound or an exterior wood filler.

Globe Handyman on Call Peter Hotton also appears in the Sunday Homes Section. He's available 1-6 p.m. Tuesdays to answer questions on house repair. Call 617-929-2930. Hotton also chats online about house matters 2-3 p.m. Thursdays: Go to www.boston.com. Hotton's e-mail is photton@Globe.com