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Chimney wall cracking

Stangob Member Posts: 26
Hello all -
Today I did some preventative maintenance on my IN 5 to get ready for the winter. I changed the sight glass and the cycle guard low water sensor. I noticed that where the flue goes into the chimney there are a lot of cracks. It seems to be separating from the wall. This boiler was installed 10 years ago and does have a chimney liner. I know I may be able to use the furnace cement to attempt to repair but that would mean turning on the boiler in hot weather to let it cure. Is there another method or another product I could use without turning the boiler on to cure the product since I have some time before starting the boiler up.
Thank you


  • Bob Harper
    Bob Harper Member Posts: 1,046
    If the liner is intact, properly sized and connected and all you need is to cosmetically seal around it there are a number of ways to do this.
    First, remove all the loose, non-viable material.
    Next, fill in the gaps with as much solid material as you can. Really pack them in as tightly as possible.
    Get some mortar mix, a pinch of stucco mix or gypsum plaster and polypropylene fibers. You can also toss in a latex or acrylic bonding additive if you aren't concerned about odors. Add the fibers and bonding additive to clean cool water. Dry mix the mortar with stucco or plaster. Be ready to work fast. Dampen the wall a few minutes ahead of time. Add the water, mix quickly and apply. We call this 'Zip mix' because it sets up so quickly. Push-fill the gaps. Add pebbles and rocks where you can to reinforce gaps. Large gaps full of mortar are what cause shrinkage cracks. Dampen the area when done and keep it damp for a day or two. HTH
  • Stangob
    Stangob Member Posts: 26
    Thank you this has been most helpful. I have found my weekend project. Thank you once again
  • mattmia2
    mattmia2 Member Posts: 9,938
    I'd dampen that stuff before chipping it off and collect and remove it. You never know when they randomly added asbestos to those sorts of products.