Why are bricks falling off my chimney?

Water, usually, and mortar that has given up

Bricks fall off a chimney because the mortar holding them has failed and, behind that, because water has been getting in. A chimney stands in the weather on all sides, and masonry is subject to deterioration, especially at the mortar joints.^[1] Once a joint is eroded, the brick above it has nothing holding it, and wind, a squirrel or one more winter can bring it down.

The bricks themselves can also fail. If the face of a brick flakes or peels away, that is called spalling, and it is a different problem from a loose brick, although the two often show up together.

The usual causes

Eroded mortar joints. The first to go is the mortar, and the National Park Service lists spalled, cracked masonry or eroded mortar joints^[2] among the signs of a moisture problem. The top of a chimney gets the most rain and sun, so the top courses typically loosen first.

Water from somewhere else. The Park Service also lists faulty roofs and gutters, including poor condition of flashing or gutters,^[2] as sources of damage. Failed flashing where the chimney meets the roof lets water run into the masonry from below. A cracked crown or a missing cap lets it in from above. Woodstock Soapstone, a stove maker, lists as part of a sound masonry chimney a crown of concrete or non-water soluble refractory cement sloping away from the chimney and sealed with a flexible material^[3] and a cap to keep out moisture, birds, or other pests.^[3] A chimney with neither is taking water straight into the brick.

Freezing. Water can also cause spalled masonry from freeze-thaw action.^[2] Water that soaks into a brick or a joint and freezes pushes the surface off.

Salts. Moisture moving through masonry carries salts to the surface. Salts deposited on the surface of masonry units are usually relatively harmless, but salt crystallization within a masonry unit creates pressure that can cause parts of the outer surface to spall off.^[1] A white powdery crust on the brick is a sign that this is going on.

Wrong mortar from an earlier repair. A patch job done in a hard, strong mortar can make things worse. The National Park Service explains that a mortar stronger in compressive strength than the masonry units will not "give," so the stresses are relieved through the masonry units, resulting in permanent damage to the masonry, such as cracking and spalling, that cannot be repaired easily.^[1] It also calls it a common error to assume that hardness or high strength is a measure of appropriateness.^[1] If a chimney was repointed some years ago and is now losing brick faces, that may be the reason.

Why it matters

A falling brick is a risk to people and the roof below. It is also a sign that the whole chimney is taking on water, and the leaking can reach the roof framing and the interior walls. Keep people and pets away from the base of the chimney until a mason has looked at it, and do not climb up to push bricks back in place.

What the repair is

The fix depends on how far the damage goes, and a mason decides that on site. In broad terms it ranges from repointing the joints, through replacing individual spalled bricks, to taking down and rebuilding the top of the chimney. The Park Service warns that it is erroneous to assume that repointing alone will solve deficiencies that result from other problems,^[1] so a competent mason also looks at the flashing, the crown, the cap and the gutters nearby. Without that, any repointing will have been a waste of time and money.^[1]

What a rebuild involves is covered in what rebuilding a chimney involves, and the cost drivers in what it costs to rebuild a chimney in Virginia. If you are not sure whom to call, read who repairs chimney masonry, a mason or a chimney sweep.

When to call a licensed pro

For the repair itself, and a mason is the right person. Virginia defines "masonry contracting" as the installation of brick, concrete block, stone, marble, slate, or other units and products common to the masonry industry, including mortarless type masonry products, and the service covers grout, caulking, tuck pointing, sand blasting, mortar washing and parging.^[4] DPOR says that if the work is valued at $1,000 or more, a valid Virginia Contractor's License is required for the license category in which the contractor is to work.^[5] Check the licence before you pay a deposit.

Call promptly if bricks have fallen once, since more will follow, if the chimney leans or has a gap between it and the house, or if a fireplace or stove vents through it. Do not light fires in a fireplace whose chimney is losing bricks until it has been inspected.

Getting help in Virginia

Loclis lists DPOR-licensed contractors with their licence number and class. Browse chimney services, see more chimney answers, or find a masonry contractor near you.

When you are ready, describe the damage once and licensed local contractors quote it.