DEAR SAM: What is the easiest way to clean a dirty garage floor?

ANSWER: For oil stains, as well as dirt, many household products, such as Savogram or Spic 'N Span, are satisfactory.

A commercial product called Duracone can also beused for garage floors and other masonry structure. This silicone water repellant, when applied to a cleanfloor, should keep it clean for a long period.

One gallon should suffice for a one-car garage of about 200 square feet. It is brushed onto the concrete thoroughly. W.R. Grace & Co., 2133 85th St., North Bergen, N.J. 07047, says Daracone makes porous masonry water repellent to a depth of 1/4 inch. It is also considered suitable for treating stucco, sandstone and cement asbestos products as well as treating water cement paint, mortar joints in glass block and glaze tile.

DEAR SAM: What can be done when the thin brass coating on a bedstead wears away and the base metal shows?

ANSWER: Brass-plated beds must be polished correctly to avoid wear. If it has a lacquer finish, it should not be polished. To clean lacquer, use only mild detergent and then wipe dry to avoid water stains. If you have a problem of peeling or wearing lacquer, it is better to strip the section rather than try to touch up the spots. Since the brass base metal is already revealed, this indicates that the lacquer is no longer protecting; you may require professional services if the areas are extensive.

You could also use Duro, a plating enamel that comes in different shades of gold. It is available in tubes with a hairbrush cap and costs 89 cents. Check withhardware stores or write Woodhill Chemical Sales Corp., Cleveland, Ohio, 44178.

DEAR SAM: I recently purchased a 22-year-old, brick veneer rambler built on a concrete slab. Crickets, pill bugs, centipedes and waterbugs are getting into the house, I think through the bottom course of bricks. Can I plug these holes with mortar?

ANSWER: It is possible that the missing mortar joints were intended for weep holes to let moisture out of the slab when it was poured. They haven't any purpose now except to let bugs in.

You should spray these openings with pesticides and then fill the joints and repoint to match the existing joints in color and style. If this doesn't help, it may be possible that the insects have settled in your house. An exterminator may be needed. Get two estimates; if a warrenty is offered, you might want to extendit for a few years until you are sure that the problem has been solved.

DEAR SAM: Would you please discuss the advantages or disadvantages of a log cabin, built of commercially marketed logs and erected by a commercial supplier. Our cottage would be located in the mountains. How warm would such cabins be in the winter? Does one need to insulate? How do the chinks hold up between the logs? Is the price comparable to other forms of wood construction?

ANSWER: You have undoubtedly received a brochure on log cabins from the commercial supplier or should obtain one, which will furnish many of the answers to your questions; however, you must realize that this specialty home - be it ever so humble - is intended as a second home and is not expected to contain central heating similar to a large home. If you include a fireplace or a wood-burning stove, this will be your primary source of heating.

Naturally, the mountains in the winter time may be colder than elsewhere. You might want to check with the prevailing area temperatures for the past few years. For a winter cabin, you will surely need insulation not only for the ceiling but or the walls, too; thus, the "cathedral ceiling" and the walls could be treated indentically with the use of two-inch Styrofoam. The exterior of the roof should be covered with 5/8-inch plyscore (exterior type) over which the Styrofoamand asphalt shingles should be applied. (R-value is 10.82)

The interior walls should have the Styrofoam applied inside to eliminate the chinks between the logs; secondly, the use of half-inch gypsum board will complete the walls by gluing with Dow Mastic Number 7 or 11.

Whether the construction cost of a log cabin is comparable to that of general frame construction, my answer is in the affirmative. If you inclination leads to the log cabin type, why not satisfy this desire, willy-nilly, a few dollars more? You could, however, obtain competitive prices from other suppliers, such as Boyne Falls Log Homes, Cross Road, Coshen, N.H. or Walpole Woodworkers, Rte. 27, Walpole, Mass.

DEAR SAM: Our large brick rambler, which was built in 1955, has a full basement that has a full story out of ground on the back. It was dry up until last year, when it started leaking during severe downpours. Water seems to come up in several places through the cement floor, which is covered with tile. The junction of the wall and floor on the front side is wet.

ANSWER: It is clear that after more than 20 years, the drainage facilities at the front wall, such as the drywells, do not absorb the water of your front gutters. Drains become clogged with leaves and debris entering from the downspouts. This causes a backup of water at the front wall and even under the floor.

You should locate the drywells at the downspouts and have them cleaned. You should check the gutters for spillovers that may also flow toward the foundation instead of away from it. I have also sent you a copy of may article on the seven key points to check if you're troubled by a wet basement.

Samuel Fishlyn includes those questions on home repairs that are of general interest in this column. Readers who wish a personal reply should include a self-addressed, stamped envelope. Allow several weeks for return. Write him at Box 62, Newton Centre, Mass. 02159.