Q: Because some bricks were loose around the front windows of our home we had a bricklayer replace them. He apparently used a mortar that had more sand than cement, and these mortar joints are now much lighter than the old ones, even though the repair is now over six months old. Would you advise us to have the repair done over, or is there any alternative to coloring the new mortar joints so they will match the old ones?

A: It is almost impossible to match any mortar to old material, and the fact that it is lighter does not necessarily indicate that it was mixed improperly. Sometimes by very carefully adding limeproof dry colors to the mortar, or by using different types of cement, colors can be matched better, but even this is iffy. If you cannot wait until it weathers out naturally, the only cure is to take out the new mortar and try to color new material to match - or redo all the mortar joints in that wall.

Q: The heating and air conditioning ducts for our first floor rooms run through our garage, which is under the house. The tops of these ducts are flush against the sandy-cement-type finish on the garage ceiling. Because of this the ducts cannot be wrapped. I tried covering what I could with fiber glass batts, but no adhesive tape will adhere to the ceiling. Have you any suggestions?

A: You can use fiber glass batts or blankets, but instead of trying to hold them up with tape, use narrow metal of plastic straps. These can be fastened to the ceiling with nails or self-tapping screws, or with small plastic anchors driven into the ceiling. Another method is to install boards of plastic foam insulation, such as styrofoam. However, because this is inflammable, it must be covered with one-half-inch-thick gypsum board. The boards can be nailed to a framework of 1x2 lumber, or held up with straps as described above.

Q: My recliner chair is covered with vinyl and has a four-inch tear on the seat. How can this be repaired?

A: It is almost impossible to do this kind of repair job satisfactorily unless the vinyl covering can be removed first. Some chairs have zippers that permit this, and some have studded nails that can be taken out to permit getting the vinyl covering. If you get it off, turn it wrong side out, hold the tear together and place a wide strip of adhesive-backed cloth tape over the tear to hold it together (duct tape is the best kind for this.) Now turn the vinyl right side out again, and carefully flow some plastic seam sealer along the cut. This special product is sold in many floor-covering stores for sealing the joints in seamless vinyl flooring. If you work carefully, a neat repair should result.

Q: When our house was built 20 years ago the basement walls were coated around the outside with a waterproofing substance. However, now when we have a heavy rain some water seeps through the concrete in several places. Is there any preparation I can apply to the inside of these walls to prevent this seepage?

A: This is one question that cannot be answered positively. It depends on how bad the seepage is, and on how much hydrostatic pressure there is on the ground around your foundation.Many paint stores and lumber yards sell coatings that are made for water-proofing basement walls. Unfortunately, there is no gurantee that they will always work. In some cases they do and in others they don't. The only sure cure is to excavate around the outside and renew or replace the waterproof membrane around the outside.

Q: I have a beautiful white baby chest that I would now like to refinish for use in my grown son's room. The problem is that it has a vinyl type finish on it. What would be the best procedure for removing this coating so I can stain or finish it in a walnut or other wood color?

A: I'm not quite sure what you mean by a vinyl type finish - it could be plastic laminate or merely a thin flexible vinyl that was glued on. Either way, I doubt that the wood underneath would be suitable for staining or finishing with a natural finish of any kind. I think your best bet is to leave the present coating on and finish over it. Clean the surface thoroughly, saidn lightly, then apply a base layer of undercoat. Then use one of the various antiquing kits to get a woodtone effect.

Q: I have a five-year-old, three-story brick house. According to an expert the roof is in good shape. However, on one of the outside wall, from the roof down to the middle of the gound floor, a six-foot-wide strip of brick gets wet after a rain, and the inside of this wall has visible traces of dampness. Must the outside wall be waterproofed again?

A: Although it shouldn't be necessary on a house that is only five years old, it is possible that mortar joints in the brickwork need repointing. I suspect the flashing around the roof line or on top of some windows on the upper floor. Also, although you have had one opinion on the roof, it may pay to call in another professional contractor to check. Pay particular attention to the gutters - they may be overflowing on the inner side and thus soaking the wall.

Q: One of my ceilings has a long crack in it and along this crack the paint is peeling in spots. There was a leak along the side of the house that has since been repaired! By this time the water should have dried out, so I was told that removing the cracked pieces of plaster, then spackling and shellacking these areas before repainting would effectively prevent cracking and peeling again. However, I am reluctant to shellac without your advice. Do your recommend this?

A: Scrapping or chipping out all the old peeling paint, as well as all plaster that is crumbly or loose, is definitely advisable. Then patch with spackling compound and sand smooth. I do not advise the use of ordinary shellac as a primer. Use either an alkyd primer sealer, or better yet, one of the shellac-base, pigmented primer sealers (sold in most paint stores). This can then be painted over with either latex or alkyd base flat paint.

Q: I accidentally spilled some white liquid glue on my highly polished walnut veneer desk and didn't discover this until well after it had dried. Is there any way to remove it without marring the finish on the desk?

A: The only answer I can give is maybe. If your desk was highly polished and had wax on it, you may be able to actually chip or scrape the glue off with a plastic scraper (like the ones used on automobile windshields). The wax may have prevented a bond, so that by scraping carefully you may be able to chip the glue loose on one edge, then peel it off. If you are careful you will not scratch the finish. If this doesn't work, you can try covering the glue with cloth saturated in warm water - many of these glues soften when wet. The trouble is, I don't know if the water will harm your finish, so test this first on an inconspicuous corner.

Q: Hot-air ducts that carry heat to the second floor are exposed in the basement so that heat is lost into the basement where it is not needed and I have trouble getting enough heat upstairs. Would adding insulation to the outside of these ducts help?

A: Wrapping the ducts with fiber glass or some similar insulation will definitely help - the thicker the better.

Q: Our finished attic is heated by radiators, but the rooms up there are never used. None of the radiators or pipes is near outside walls, and I was planning to close the shut-off valves to those radiators to conserve fuel. Is there any danger of the pipes or radiators bursting, and will this conserve fuel?

A: As far as danger of pipes burning, this will only happen if they freeze, and I cannot tell for sure whether this would happen. I doubt it, but it depends on how cold it gets and on how well the walls upstairs are insulated. As far as fuel saving is concerned, there will be some, but bear in mind that it may not be as much as you expect. If there is no insulation in the floor of the attic, a considerable amount of heat will be lost up into the attic if it is unheated - and this may be enough to negate the savings you would expect.

Q: We are having quarry tile installed on our kitchen floor. Should it be treated with a sealer, and if so, what kind?

A: The answer is yes. Use one of the clear sealers made for use on terrazzo and stone - sold in most paint stores and by stone dealers.

Questions about home repair should be addressed to Do-It-Yourself Clinic, The New York Times, 229 W. 43d St., New York, N.Y. 10036. Questions of general interest will be answered in this column, but unpublished letters will not be answered individually.