What causes water damage?

When water enters a chimney and freezes, cracks are created that let more water in. The rate of deterioration increases each year. As more cracks are formed the water can eventually soak into the house roof or walls.

Water can enter a chimney through gaps in the crown and mortar joints, deteriorated or porous brick, or through the flashing. When the water evaporates it draws soluble salts to the surface which show up as a white powder called efflorescence. The area where the efflorescence appears can often be used to determine the source of entry of the water.

The chimney may have been soaked from the inside by the cool exhaust from an efficient furnace traveling too slowly up an oversized flue. These conditions can result in acidic condensation forming in the upper, cooler part of the flue and running down the inside walls, soaking the masonry. Installing the properly sized liner will keep the flue gasses warm enough that condensation doesn’t form.

Water can also enter the chimney through uncovered flues. These should be covered with a rain cap or top mounted fireplace damper. Unused flues should be sealed off with sheet metal or masonry.

Chimneys must be allowed to breathe so that any vapor that has found its way into the chimney can escape. Chimneys with a water tight coating such as paint or certain waterproofing products will deteriorate much more quickly than uncoated chimneys if water finds its way behind the barrier. Painted chimneys must be regularly touched up, especially at the top. The crown must be intact and rain caps in place.

How can we help?

Application of a clear vapor-permeable water repellent is often recommended as part of the solution to a wet chimney. A high quality repellent will soak into the masonry forming a strong interior bond with the silica found in masonry. Vapors are allowed to escape but rain cannot soak in. Water repellents that form a surface film must not be used.

While larger cracks in the chimney need to be ground out and pointed, fine cracks may be sealed with a brushable vapor permeable elastomeric sealant. We use a product that has proven itself over many years.

Flashing is used to prevent water entry between the chimney and the roof. It may need to be sealed, repaired, or covered with a flexible, fiberglass mesh reinforced long lasting sealant.