Understanding Chimney Brick Porosity and Water Damage

Chimney bricks, much like a sponge, possess a porous nature. When faced with heavy rain, chimneys absorb a significant amount of water. However, just like a saturated sponge, there’s a limit to the amount of water bricks can hold. Once that threshold is reached, water leakage into your home becomes inevitable, resulting in interior damage.

Below, you’ll find images illustrating the consequences when bricks can no longer repel water and instead allow it to infiltrate your home.




Water Damage Manifestations: Beyond Leakage

Water damage doesn’t just manifest as leakage; it takes various forms that can impact your chimney’s overall health. These manifestations include unsightly staining, reduced insulation effectiveness, gradual deterioration, and, in the worst-case scenario, structural failure.




Brick Water Retention and Its Consequences: Moss Growth

Excessive water retention in your chimney’s bricks can also foster the growth of moss, which poses a significant threat to mortar joints and crowns. (Explore our Chimney Moss Removal Page for more information on moss removal.)




The Freeze-Thaw Cycle: A Threat to Chimney Integrity

Damage to chimneys can be particularly pronounced during the freezing winter months. When water inside the bricks freezes and expands, it exerts pressure on the brick’s structure, potentially causing structural integrity damage. Few factors are as detrimental to a chimney’s stability as water.


To safeguard against water damage, proper protection is essential. Chimneys require waterproofing solutions specifically tailored for bricks and mortar. Standard water sealers available at typical hardware stores are ill-suited for chimneys as they merely act as surface sealers and silicone coatings, forming a water-resistant film that traps water vapor. When these vapors cannot escape, they contribute to brick deterioration.


Painting your chimney won’t resolve the issue either, as it simply seals the surface, hindering the chimney’s ability to “breathe.” This can lead to mortar damage and spalling, as water and water vapors still need a pathway to exit the bricks.




Prioritizing Proper Brick Ventilation for Your Chimney

Ensuring that the bricks in your chimney can “breathe” is of paramount importance. Off-the-shelf waterproofing solutions from local hardware stores, including chain hardware stores, can create the same issues as chimney painting.


The product we use is a non-film-forming water-repellent that goes beyond surface sealing. It effectively penetrates and lines the masonry pores to shield the brick from water damage. What sets it apart is its 100% vapor permeability, allowing water vapor trapped within the brick to easily escape. This unique quality permits the chimney to breathe freely while keeping water at bay.




Chimney Moss Removal and Waterproofing: A Precise Process

Before applying waterproofing, it’s crucial to address any existing moss on the chimney. We conduct thorough chimney moss removal in accordance with the Manufacturer’s specifications to ensure proper preparation for waterproofing. Additionally, if lime leaching or remnants from prior chimney repairs are present, we perform an acid wash on the chimney, adhering to the Manufacturer’s guidelines, before applying the waterproofing. These steps are essential to maintain the warranty’s validity, as the Manufacturer requires their completion.


Our chosen product includes an impressive 10-year Manufacturer’s Warranty, providing you with a decade of worry-free chimney water protection. Metro Chimney follows the Manufacturer’s recommended application instructions meticulously. Upon completion, we’ll provide you with a Warranty Card that you can easily fill out and submit to the Manufacturer, securing your 10-year protection.



*It is important to note that a chimney must be fully free of moss to apply this product per manufacturer’s instructions (Click here to see our moss removal page). It also cannot be applied until 24 hours after moss removal to allow the PH in the chimney to return to normal. It also must be applied on a dry day that is above 40 degrees.

**We must wait for a full 28 days following a chimney repair to apply this product per the manufacturer’s instructions. This is to allow the new mortar work to cure enough to allow the water proofing to have full penetration.

***It is best to do this service in the dryer spring and summer months, but we can do this on any day of the year so long as it is not raining.





I e-mail bids only to give you all the information you need to make an informed decision for the work. If you contact me for a bid, please give me a correct e-mail address. Also, I may need to contact you via phone prior to e-mailing you the bid if there is work that needs to be done in addition to what you originally called for due to structural, code, or safety reasons, or if I need any further information not provided during your first call to schedule me to come out to do the bid.






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