Q. I have a brick chimney built thirty years ago. When there are high south-easterly winds, accompanied by heavy rain, I get a lot of water in my basement through the chimney clean-out doors. I tried covering the two flue tops temporarily, but it didn’t make any difference. I tried treating the chimney with a sealer, but that didn’t help either, it still leaks like a sieve.

My main frustration is that no one seems to be able to tell me what to do. I contacted the so-called experts recommended by my friends but all to no avail. I plan to get my chimney repointed and resealed this summer but I’m not sure if this is the right answer. Can you offer a suggestion? G. E.

A. Since you tried covering the tops of the chimney flues and it still leaked, the water must be coming in from another location. Given the age of the chimney, a number of things are possible. A common problem is corroded flashing at the juncture of the chimney with the roof. After years of exposure to the elements, metal flashing, usually made from sheet aluminum or copper, will eventually corrode and require replacement.

To replace the flashing, the shingles will have to be removed around the chimney and the chimney top will have to be rebuilt from the roof up. Alternatively, removing mortar at the brick joints to insert new flashing is possible, but this will not result in as good a job as rebuilding the chimney top. If the flashing is still in good shape, it’s possible the bitumen sealing the flashing laps has failed, in which case installing new bitumen at the flashing joints may solve the problem.

Another problem frequently found in areas of high exposure is a cracked chimney cap. The cap is usually constructed of concrete with a flashing installed under it. The cap flashing should extend from the clay liner out to the drip edge of the concrete cap. If water enters through cracks in the cap, deterioration of the concrete and flashing accelerates due to the freeze-thaw cycle.

In the worst case, the walls of the chimney may have cracked and failed at the mortar joints. Again, the freeze-thaw cycle speeds up the erosion, and repointing – replacing the mortar between the bricks – may not work in serious cases where the cracks extend into the clay liner of the chimney. If the liner is cracked, it must be replaced by rebuilding the chimney. Repointing is only satisfactory for repairing cracks in the outer brick wall of the chimney. Similarly, a sealer is useless for repairing cracks which extend through to the liner.

To locate the source of the leak, hold a mirror in your fireplace at a 45° angle and shine a flashlight up into the flue with the damper open. At the same time, have a friend spray water with a garden hose on different parts of the chimney on the outside. Do the inspection and water test when it’s not raining so you can better identify the point of water entry.

The chimney should be inspected by a fire prevention officer and a qualified mason. The fire prevention officer will assess the chimney condition as per the latest fire safety standards and give a detailed report of the remedial work required. The mason will be able to ascertain the amount of repairs or rebuilding necessary and provide a cost estimate.

A common misconception about brick construction is that it is maintenance-free. Even the best built brick wall or chimney requires repointing after a number of years. In exposed areas, the mortar eventually cracks and loosens, creating a dangerous situation where bricks can fall out and injure people below. Regular maintenance of chimneys and other building components minimizes deterioration and ensures safety over the life of the building.