previous
  • 9 Concrete Countertops Ideas
    9 Concrete Countertops Ideas
  • 7 Trim Carpentry Secrets
    7 Trim Carpentry Secrets
  • Video: Build a curved step
    Video: Build a curved step
  • Shorten a Prehung Door
    Shorten a Prehung Door
  • Tips & Techniques for Painting
    Tips & Techniques for Painting
  • The Passive House Build
    The Passive House Build
  • 12 Remodeling Secrets
    12 Remodeling Secrets
  • All about Roofing
    All about Roofing
  • Clever daily tip in your inbox
    Clever daily tip in your inbox
  • Deck Design & Construction
    Deck Design & Construction
  • Remodeling in Action
    Remodeling in Action
  • Magazine Departments
    Magazine Departments
  • Master Carpenter Videos
    Master Carpenter Videos
  • Energy-Smart Details
    Energy-Smart Details
  • 7 Smart Kitchen Solutions
    7 Smart Kitchen Solutions
  • Buyer's Guide to Insulation
    Buyer's Guide to Insulation
  • How to Install Housewrap Solo
    How to Install Housewrap Solo
  • 7 Small Bathroom Layouts
    7 Small Bathroom Layouts
  • Read FHB on Your iPad
    Read FHB on Your iPad
  • Basement Remodeling Tips
    Basement Remodeling Tips
  • Electrical Articles & Videos
    Electrical Articles & Videos
  • The Hobbit House and More
    The Hobbit House and More
  • Play the Inspector Game!
    Play the Inspector Game!
next

How to Repair Hairline Cracks in Chimney Mortar

Q:

During a recent heavy rain, I noticed a steady drip near my fireplace. The drip indicates a leak somewhere around my chimney. I’m not sure if the water is getting in through mortar joints (some have hairline cracks) or through the brick. Is there a way to seal the brick and the cracks? I’ve ruled out all other entry points.



Mike Guertin, East Greenwich, RI


A:

Cody Macfie, owner of Steep Creek Stoneworks Inc. in Brevard, N.C., replies: In terms of water entry, the most-important part of a chimney is the flashing. If the flashing isn’t installed properly, sealing the brick and the mortar joints will be about as productive an endeavor as trying to have a conversation with a fish. If you’re sure the flashing is fine, though, and you have eliminated all other potential problem areas, sealing the brick and the mortar is inexpensive and easy.


To seal mortar cracks and brick, I use a waterproof sealant by Prosoco called Siloxane PD (www.prosoco.com; about $25 a gal., available at most masonry-supply stores). I don’t add water to the Siloxane PD, and I like to apply it with a garden sprayer so that I can spray it directly into the cracks. After all cracks have been filled, apply a couple of layers of Siloxane PD over the entire chimney to seal the brick.


Seal the cracks before they’re too far gone. Hairline cracks in brick and mortar can be sealed. The larger cracks in this chimney cap should be repointed before penetrating sealant is applied.

Seal the cracks before they’re too far gone. Hairline cracks in brick and mortar can be sealed. The larger cracks in this chimney cap should be repointed before penetrating sealant is applied.

Photo by: Daniel S. Morrison
Inspect the flashing. Improperly installed flashing can cause major water damage. Unlike this application, flashing should tuck into the mortar joints and fold around the chimney’s corner

Inspect the flashing. Improperly installed flashing can cause major water damage. Unlike this application, flashing should tuck into the mortar joints and fold around the chimney’s corner

Photo by: Daniel S. Morrison
From Fine Homebuilding 196, pp. 90 May 14, 2008