Sagging Floors Don’t Have to Be Costly Fix

QUESTION: We recently purchased an older home at a reasonable price. The living room floor sags noticeably in the center. A friend says the floor joists probably are bad and need to be replaced--a major repair job. Is this usually the case?

ANSWER: When sections of flooring become uneven, usually a problem in older homes, the cause is seldom the joists but more often the weakening of the girder (structural member that runs beneath and at right angles to the joists) or supporting post.

One remedy is to merely add another post directly beneath the sagging section of girder. Rent a shoring jack and use it to raise the girder to level, plus a fraction of an inch more to allow for settling. Raise the jack very gradually, a partial turn or so a day over the course of a week or more.

Adjust the height of the new post and make sure there is solid footing beneath (a 20-inch-square concrete slab 10 inches thick is standard). Then fit the post, check that it is exactly vertical, and lower the girder onto it as you remove the jack. Sometimes all that is necessary is to place shims between the girder and existing posts, using the same jacking method.

To determine the amount a girder must be raised to level it, stretch a string along one side of the beam, from the bottom corner at one end to the bottom corner at the other. The amount of wood showing below the string (where the sag is most extreme) is the distance the girder must be raised.

Electric Water Heater Leaves Him Cold Q: We remodeled our kitchen and replaced our 40-gallon, gas-fired water heater with an electric water heater that has a 5,500-watt element. Now we are stuck with a tank that is good only for me and my wife. When our three grandchildren come to visit, the water is not hot enough for them to bathe at half-hour intervals, like they did when I had a gas-fired water heater. Can you help?

A: People switching from a gas-fired to an electric water heater frequently cite the problem you discuss. When selecting a water heater, consider its capacity and the recovery rate. The recovery rate is the number of gallons that the unit will heat to 90 degrees to 100 degrees Fahrenheit above its inlet temperature in 1 hour. When the tank capacity is low, the unit must have a high recovery rate to have an adequate supply of hot water. As an example, a typical oil-fired water heater has a 30-gallon capacity and a 120-gallon-per-hour recovery rate.

Electric water heaters, on the other hand, have a low recovery rate: usually about 18 gallons an hour, although some units have a 22-gallon recovery rate. Unless there is a large tank capacity (on the order of 60 to 80 gallons), a simultaneous longtime demand for hot water will result in an inadequate amount of hot water being supplied to the fixture.

You can increase your heater’s hot-water output by installing a pre-warming tank in series with the water heater. The cold-water supply is connected to the pre-warming tank’s inlet and the tank’s outlet is connected to the water heater’s inlet.

By boosting the temperature of the water entering the water heater, you improve its recovery rate. It is also more economical because you are not electrically heating a large volume of water all day, so there will be sufficient supply during the peak periods.

On Spores and Ceiling Chores Q: The cathedral ceiling in my 10-year-old house was OK until five years ago, when we noticed black spots appearing through the sand finish. I painted it and it looked good but the black spots came back. No matter what I do, they come back. I have asked many carpenters what causes it, but none seem to know. Can you help?

A: The black spots are probably mildew spores. Mildew is a fungus and unless you kill it, it will come through a new layer of paint, especially a water-based paint. Try washing the ceiling with a solution of bleach, detergent and water. After the ceiling is dry, paint it with a mildew-resistant paint or use a fungicide additive in the paint.

Low-Radiant Heat Makes a Pooch Smile Q: The plans I have for building a year-round doghouse state that low-radiant heat can be used during the cold winter months. Just what is low-radiant heat and where can I get the parts needed to install it?

A: This type of heat radiates directly to objects so it doesn’t have to heat the air around them to have a warming effect. Low-radiant heat is usually supplied by electric cables embedded in floors or ceilings.

To protect the cables from damage by the animals, place the cables in a bed of sand over polyurethane insulation and a vapor barrier followed by a minimum of 3 inches of concrete.

Some low-radiant heating cables can be laid directly in the concrete but insulation is still required to keep bottom heat loss to a minimum. Use Styrofoam panels for this purpose.

Protect all wiring in metal conduit so your dog can’t chew it.

Simple Ideas to Help in the Workshop Here are some timesaving tips and hints that can make life easier for you in the workshop:

* Small particles of steel wool can collect on a piece and even become airborne as metal dust. To contain them, wrap a small or medium-size magnet in the wad of steel wool.

As you work, periodically wipe off the magnet. When the job is done, run the magnet over the work to remove remaining metal particles. Always wear a dust mask when working with steel wool.

* The front end of a wire brush always wears out before the rest. To give new life to the brush, clamp it in a vise and saw off the front inch or so.

* To convert an old paintbrush into a light-duty scrub brush, wrap the bristles securely with masking tape. The closer the tape is to the tips of the bristles, the stiffer the brush will be.

* Restore the cutting edge of your craft knife by rubbing the blade a few times on the striking surface of a matchbox. Sharpen both sides, holding the blade at a low angle that matches the blade’s bevel.

* If you need to carry a razor blade to a job, tear the matches out of a matchbook, insert the blade and close the cover. Carry a craft knife in a plastic toothbrush holder.

In your workshop, store single-edge razor blades in slots cut into a small piece of rigid foam packing material.

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To submit a question, write to Popular Mechanics, Reader Service Bureau, 224 W. 57th St., New York, NY 10019. The most interesting questions will be answered in a future column.