Do chimney leak repair kits work?
Short answer. Chimney leak repair kits work for a narrow set of problems: porous brick soaking up rain, hairline cracks in the crown, and small gaps in otherwise sound flashing. They do not fix missing or rusted step flashing, counterflashing that has pulled out of the mortar, a broken crown or a missing cricket, which are the most common causes of chimney leaks.
What is typically in a kit
- Masonry water repellent. A breathable siloxane or silane sealer that keeps brick and mortar from absorbing rain while letting vapor escape.
- Crown sealer. A brushable elastomeric coating for hairline crown cracks.
- Flashing sealant. A thick elastomeric coating or tape for seams in flashing.
When a kit is the right tool
- Water shows up only in long, driving rains, and the brick looks dark and saturated afterward.
- The crown has fine cracks but is not broken or crumbling.
- The flashing is intact and properly layered, with one small gap at a seam.
When a kit will not fix it
- Step flashing is missing, rusted through, or was installed as one long piece instead of overlapping steps.
- Counterflashing was never cut into the mortar joints or has pulled away.
- There is no cricket behind a wide chimney, so water pools against the uphill side.
- The crown is broken, the cap is missing, or a framed chimney's metal chase cover has rusted.
Sealant smeared over failed flashing usually buys a season. And a non-breathable paint or coating on brick can trap moisture that later pops the brick face off, called spalling.
Before buying anything
Find the source. A hose test, with one person running water low on the chimney and working upward while another watches inside, tells you whether it is brick, crown, cap or flashing. See chimney leaks and crickets and roof flashing explained.