Masonry Chimneys

What should I know about the condition of a masonry chimney? What is a mortar wash? What are chimney caps used for? These are all good questions that deserve a valid answer.

The proper functioning of the masonry chimney that is usually located at the top of the house roof is crucial to the operation of the combustion appliances connected to it. Normally connected to the home’s heating unit and domestic water heater. Sometimes, if there are two separate chimney flues, one can be used with a fireplace and the other with a furnace or boiler.

Most masonry chimneys are made with concrete or cinder block and than covered with brick. At the top of the chimney, a concrete flashing is used to cap the masonry unit’s structure and keep rain water out and penetrating inside the chimney. These cement washes, however should not be considered by themselves a long term solution to guard against moisture penetration. All cement washes should be covered with a metal chimney cap to keep the rain water out.

Over time the chimney can develop severe damage and deterioration due to water seepage inside the masonry structure. A white powdery substance can develop on the outside surface of the chimney indicating that moisture has penetrated the chimney and is evaporating from inside the brick, hence the term given is efflorescence.

However there may be other internal forces at hand that can lead to additional deterioration of the masonry chimney’s internal components. Most modern home heating appliances use either gas or oil. During normal operation of the house’s heating appliance, a natural by product of combustion is the creation of water vapor. If the chimney is not properly sized or lined for the combustion to properly take place while discharging the water vapor out of the chimney, a lot of deterioration will develop over time due to excessive condensation water left inside the chimney.  The result will be damage to the inside of the masonry chimney.

So in conclusion, to adequately check a masonry chimney first look on the exterior for any obvious damage. Than if possible go on the roof and check the chimney top. It is highly recommended to hire a chimney sweep to clean and than inspect the interior of the chimney for loose or broken components.

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