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Exterior chimney repair

Posted by navigator (My Page) on
Fri, Jun 17, 11 at 13:06

I have an old house in southern Vermont with a chimney that is worse for wear after this past winter. The two plus story chimney is made of brick on the lower half and cement block for the remainder. The entire chimney has been coated with thin cement product (guess) and/or Thoroseal. Over the winter a large section of the lower half (brick) lost this cement/paint coating. There is a a 2x2 section of brick that is badly deteriorated. The mason that installed a new cap 4 years ago gave me two options: 1. Rebuild chimney (costly-- no thanks) or 2. Repatch and hope, no promises made as to how long. Question: Would it make any sense to add another "layer" of bricks (encasing 3 exterior sides of chimney)on the lower half of the chimney? This approach might slow down further deterioration of the chimney. Thoughts? (I have photos but the site does not accommodate.)

Follow-Up Postings:

RE: Exterior chimney repair

I'd check with another mason or two. Parging (the masonry coating over the brick and block) can be repaired. Adding various epoxy/plastic compounds and polypropylene fibers to the parging mortar can strengthen it a good deal. A silicon based water proofing can also be applied after the parging dries.

Exterior chimneys in cold climates are subject to extreme freeze and thaw cycles which are very hard on coatings. Repairing the parging and then building some sort of chase around the chimney to prevent water on the masonry itself should help considerably.

RE: Exterior chimney repair

Obviously water is getting into the brick work and freezing in the winter. For the chimney to survive you need to patch it and keep water out of it.

RE: Exterior chimney repair

I appreciate the comments/suggestions for repairing my chimney and thought I should provide some feedback after actually making the repairs. Although time will tell, I repaired the chimney by initially filling in the deep divots with surface bonding cement-- about $14 per 50 lb bag at my local building supply store. It has fibers in it. For the deeper divots in the brick I had to apply a second layer. I then covered any remaining exposed brick with a thin coat of the bonding cement. There is some "art" to getting the right consistency; but it does adhere to a vertical surface. I allowed it to dry for a few days and then "painted" on a batter-like consistency coat of Thoroseal ($33 per 50 lb) with Acryl 60 admixture. When I return in the fall I will give it a second coat. Thanks for your comments!

RE: Exterior chimney repair

Keep in mind that the water that is causes freeze damage can come from the top, sides or bottom. In your case, it could be wicking up from the ground level.

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