Water is a Masonry Chimney’s Worst Enemy

Brick and stone are used in construction because of their aesthetic and durability, however, these materials, along with mortar, are susceptible to water damage and need to be maintained to prevent failure.  Since restoration or reconstruction is costly, it is important to keep a watchful eye on any chimneys in a home.

Bricks, stones, and mortar all absorb rainwater to some degree based on their density and hardness. Some of these masonry materials, such as soft-type brick, absorb and retain water more easily than hard-type brick. Unfortunately, many builders use soft brick since the cost is lower, and problems usually won’t show up for several years after a structure has been built and they are long gone.

Spalling bricks and missing mortar due to water penetration

All types of masonry should be treated with a professional water-repellant sealer every two to five years. The sealer will reduce penetration of water into the masonry by causing the water to bead up. This process alone can save homeowners thousands of dollars. Without water repellant, the masonry will absorb moisture, go through freeze/thaw cycles, and at some point will begin to spall (faces pop off). In severe cases, mortar is washed out and bricks may fall out.

The next area of concern is the cement cap, otherwise known as a wash, splay, or crown. The cement cap acts as a roof for a chimney, and if properly built will shed water away from the top portion of the chimney rather than directing rainwater onto the masonry. This area is the most common space to find damage to the masonry since most cement caps are not built properly and to International Residential Code requirements. The IRC requires a 4” thick cap with a 2” drip edge and drip channel, with bond breaks around the flue tiles to allow for expansion. A properly built cap will last for many years and will help protect the masonry below it.

Finally, faulty flashing is often a source of leaking into the attic or other floors of the home. If water damage is found next to a chimney at the ceiling area, suspect the flashing as the first place to look. Gaps or missing pieces of flashing, or unsealed areas will likely be areas of concern that need to be addressed with sealant, repair, or replacement.

If your chimney is spalling, has deteriorated mortar,  a cracked or improperly built cement cap, or leaking issue, contact your local chimney professional for help. 

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Marge Padgitt is a 40-year chimney industry veteran and the author of Wood-Fired Heating and Cooking. Website: www.chimkc.com. 

Masonry chimney repairs should be done in the spring

By Marge Padgitt

Badly spalling bricks on a chimney

If there are pieces of bricks or stones lying around the yard or driveway, it could be a sign that masonry repair is needed. The first place to look for damages by cold, freezing rain, and wind is the chimney since it is the area most exposed to the elements.

Signs that repairs or rebuilding is needed are missing or deteriorating mortar joints, cracked bricks or stones, or faces of masonry popped off. This is due to the penetration of water into the masonry- and when water freezes it expands, which usually results in the face of a brick or stone breaking off.

Badly spalling bricks

Unfortunately, many chimneys are built with soft type bricks rather than hard type bricks due to the cost.  Soft bricks absorb moisture more easily than hard bricks. After a few years, the soft bricks will begin to show damage, but after 30 years any type of brick or stone chimney will likely show damages of some type, if only to the mortar joints.  In some cases, masons have found completely deteriorated bricks with hard mortar left behind. In other cases, the bricks are good but the mortar is severely deteriorated or missing altogether. When this occurs it is a sign that the wrong type of mortar was used.  For this reason, the Midwest Chimney Safety Council recommends that chimneys should be built or reconstructed using hard bricks and the right type of mortar which will last many years longer than those built with soft masonry units.

Mortar deteriorated so badly that
the chimney is falling apart

Mortar sets up better when the work is done in the spring when temperatures are moderate so the curing process can complete without issue. If the temperature is too cold, the mortar can crack and take a long time to cure. If the temperature is too hot the water in the mortar may migrate to surrounding masonry and shrink. Professional masons can control some of this by adding an accelerant in cold weather or soaking bricks in water before using them in hot weather, but they much prefer working with masonry in ideal weather conditions.

Cement cap with drip edge

The cement cap (crown) should be inspected in the spring to assure that it is in good condition with no cracks, deterioration, or lifting. The cap serves as a roof for the chimney and keeps the elements out of the interior chimney chase where rain can cause damage to the interior flue, smoke chamber, damper, and firebox. Any small cracks or gaps should be filled with high temp silicone, but if large cracks, severe deterioration, or missing sections of the cap exist a new cap should be constructed.  As of 2012, the International Residential Code required a poured formed crown with a drip edge to better protect the chimney from damaging rainwater. The old-style crowns with a slope but without a drip edge actually contribute to the fast deterioration of masonry at the top part of the chimney, so this newer style is a big improvement.

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Marge Padgitt is the CEO of HearthMasters, Inc. and HearthMasters Education in Kansas City, Missouri. Contact her at hearthmastersboss@gmail.com.