Preserving Masonry

The Damaging Effects of Water to a Masonry Chimney

Chimney repair

Waterproofing ruined this chimney

Many people who are in need of a  Lunenburg ma chimney repair ask me how their chimney has become so deteriorated, and it’s usually from water damage, strangely enough.  Let’s think about it for a moment. Everything on the exterior of your home below the roof line is protected from the elements to some degree. Protected by the overhang of the roof, and eave, all provides shelter from rain and snow. Only the chimney sticks up past the roof line without protection from the weather. Day in and day out the chimney takes all the brunt of Mother Nature, the wind driven rain, freezing rain and snow. Year after year it endures the freezing and thawing cycles.

A masonry chimney is built using brick or stone, concrete blocks, mortar and steel. These materials seem very durable, but their main weakness is the freeze and thawing of moisture. The materials used to construct a chimney are susceptible to deterioration of the freeze and thaw cycles, making it important to construct a chimney properly.

Should water enter the structure the material will be subjected to expansion when it freezes. This is damaging to masonry and is the cause of the majority of masonry repairs in colder climates and has led to numerous Boxborough ma masonry repair.

Water intrusion can cause damage to the wood structure behind the chimney as well. It is a common building practice to use a 30 pound felt paper, commonly referred to as “tar paper” behind the chimney. It is essential to have a moisture barrier between any masonry on the outside of your home, including steps, and veneers to prevent the transfer of moisture from the masonry structure to the wood framing behind it. Some of the things a masonry contractor or inspector should look for when inspecting a chimney are:

Spalling of the brick face

Cracked bricks

Missing mortar joints

Mortar that is flaky and rotted in appearance

Rusted Dampers

Rusted fireboxes (if applicable)

Rotted siding

Water damage to the interior around the area of the chimney

Water seeping in the basement at the base of the chimney

Cracked or broken flue tiles

How do we stop or prevent water from damaging a masonry chimney?

Here are a few of the simpler and effective methods:

A metal rain cap

These caps also called spark guards, or chimney caps are perhaps the easiest and most effective way to keep moisture out of the inside of a chimney. They can be purchased for less than a hundred dollars and if you can reach the top of the chimney with a ladder, can be installed by anyone with basic handyman skills. For every appliance attached to your chimney there is a corresponding flue pipe. The fireplace has the largest flue and it is the main priority for installing a metal cap. Furnace flues are relatively small and an oil fired furnace should evaporate any rain or moisture that gets into the flue pipe. The added benefit of these caps is it keeps leaves, bats, birds and even raccoons out of the chimney.

Repair minor damage now

Nine out of ten times the chimney crown is the first thing to fail on a chimney. If this can be caught early, it will prevent a more expensive chimney repair down the road.  The crown is the first line of defense the chimney has and is an essential part of a long lasting chimney. The chimney crown should be pitched away from the flue liners and cover the entire top portion of the chimney. Many chimney crowns are improperly built using simple mortar mix, but mortar should never ever be used on the chimney top like this.  It simply is not designed for this function and will crack and flake off. It is not uncommon for a Marlborough ma masonry contractor to repair a crown built with mortar a year after it was built.  It is essential to build the crown using Portland cement mixed with sand. This is essentially a concrete mix and it should be a minimum of one and a half inches thick. If built like this the top will withstand the elements for many years.

Repair the flashing

If you look up at where your chimney meets the roof line, you will be able to see metal lead flashing. This flashing seals off the space between your chimney and the roof, allowing rain and snow to run down the roof and not into your living space. Should you need your chimneys flashing fixed, an experienced chimney repair contractor can inspect, repair and replace this lead flashing. It is common to replace this flashing when your roof has been replaced.

Be cautious about waterproofing!Damaged brick building

Due to the design of a masonry unit, it will both absorb moisture and allow the moisture to evaporate back out. This is an essential function and should not be closed off. Applying a product that creates a membrane over the exterior of the masonry will always trap moisture inside. Despite what one would think it never prevents all the moisture from penetrating in.  If the function of evaporation is shut off, the freezing and thawing will be much worse and will cause very rapid deterioration of the structure.  Several products are designed specifically to allow the masonry to “breathe” and are called water repellants, not water proofing. Nit picking I know. The correct term is vapor permeable, meaning that water can evaporate out of the masonry. These products drastically slow water intrusion. Paint also should not be used in a manner to water proof masonry, as it will simply trap the moisture inside as well.

To conclude:

Preserving masonry

Chimneys in Massachusetts are quite durable and any damage will not happen overnight. It will be slow and subtle. Once it is noticeable it could be a serious repair.  The best prevention is to visually inspect your chimney often. Anything that seems wet, flaking or cracked should be inspected right away.


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