Are chimney sealants a good idea?

The chimney is one prominent part of the home that is constantly at the mercy of the fluctuating weather. As weather patterns shift through the seasons, the baking sun, rising humidity, driving rain, and deep freeze of the outdoor elements can take a toll on the brickwork, and while bricks are a naturally resilient building material, they can still take on a considerable amount of wear damage over time. One common option for combating the threat of moisture and water is a brick sealant — but, is a sealant the right idea? Here are the points to keep in mind before committing to a sealant for your chimney.

Because bricks are a porous stone material, they naturally have minute pores which can absorb any moisture that comes into contact with the bricks. Once the liquid moisture is in the bricks, and the temperature drops, the moisture freezes and expands, causing larger cracks and spalling. Applying a waterproof sealant creates a layer of the surface of the bricks that stops the moisture from absorbing into the brick’s surface. This is the major pro of a sealant — preventing liquid from entering the brickwork and causing cracks. From here, we need to focus on the material being used in the sealant.

Circling back to the porous nature of brick, the small crevices are a necessary element to maintain the integrity of the material itself, because they allow the brick to naturally pass water vapor through the surface of the brick. Be careful about the type of sealant being used on the chimney, because many types found in hardware stores will simply fill in all of the natural pores in the brick, trapping water vapor within the brickwork, without providing a natural escape or evaporation route. If water vapor is trapped within the brick, it will find the path of least resistance out of the brick in some fashion, which can lead to cracks and spalling, on the exterior or interior of the brick. Naturally, this is a con, and should be avoided.

That said, there are sealants that are vapor permeable, which coat the exterior brickwork with a layer of protection from liquids, but still allow the pores of the brick to “breath”. These sealants provide the maximum amount of protection from weather conditions, while creating a minimal amount of risk to the underlying structure of your chimney. If adding an extra layer of protection against liquids and weather sounds like a good idea for your chimney, a 100% vapor permeable sealant is the best choice.

To ensure that the best sealant is applied to your fireplace correctly, and for general questions about keeping moisture out of your chimney, consult the professionals at Lindemann Chimney & Fireplace | Heating & Cooling at (847) 739-4199, or you can reach them online!