QUESTION: We have a brick patio, and the spaces between the bricks need to be filled - again. I've tried two kinds of sand, but it washes away in a few months. What is a good way to fill the spaces, and when is the best time?ANSWER: The problem is probably not the sand, but the slope of the patio. A slight slope (one inch for every four to eight feet) is necessary for proper drainage. Too little slope, and rainwater settles into low spots, eventually softening and washing out the sand and the subbase material beneath the patio. Too much slope, and the sand washes out continually.Correcting the problem starts with the subbase, the combination of crushed stone and sand that sits below the patio. Take up the bricks, then build up low spots or lower high spots by adding or subtracting subbase material. Check after it rains; if the patio still isn't draining properly, you may need to make additional adjustments.A dry spell is the best time for adding sand; just sweep it in between the bricks.

QUESTION: I have a problem with moss and lichen on my aging roof. I'm going to sell my house this spring, and I think it makes a terrible impression. But I imagine power-washing won't help the shingles, which are all right but nearing the end of their useful life.ANSWER: It's true, curb appeal sells about 50 percent of houses, but it's probably too late to begin cleaning those shingles now, and it wouldn't be cost-effective.Even if your shingles were new, power-washing wouldn't be a good idea. Water pressure can remove the coating from asphalt shingles; that shortens their lives and probably compromises any warranty the roofer and the manufacturer provided.Remember, Pennsylvania laws require disclosing the age and condition of a roof during the sale of a house. How this will fit into negotiations with prospective buyers is something you and your real estate agent need to discuss.

QUESTION: A plumber I hired to repair a release valve on my water heater told me I needed a chimney liner. Because my new high-efficiency gas furnace is no longer vented through the chimney, he said, there isn't enough constant heat, and that will crack the chimney.ANSWER: Your furnace contractor should have told you all that when he installed the furnace, which is probably vented through polyvinyl-chloride (plastic) pipes through the basement wall to the outside. The plumber is saying that without the furnace, the chimney flue is too big to vent the water heater alone.Condensation is created inside a chimney from the water-vapor byproduct of natural-gas combustion. Your old furnace probably generated enough heat to dry out the chimney flue. By itself, though, the water heater doesn't generate much heat, and the resulting buildup of moisture could cause the chimney to deteriorate.A liner will protect the chimney's masonry. But a better solution would be to install a corrugated metal pipe that snakes down the chimney and connects the furnace to the exhaust pipe of the water heater. Because of the narrower pipe, the water heater's warmth will be enough to prevent condensation. Other gases produced by the furnace would be exhausted instead of being forced down into the basement by cold air.Send questions to Alan Heavens, The Philadelphia Inquirer, Box 8263, 400 N. Broad St., Philadelphia 19101 or aheavens@phillynews.com