I have a large crack where the fireplace hearth meets the chimney. I’m curious if this is a foundational problem, and if it needs to be repaired by a pro, or if I should just use a sealant repair product.

cracked mortar

right side


  • 2
    Age of house &/or chimney? What does it look like from below, or is it on a slab so there's no "below?" Tht looks more like "hearth meets the chimney" than "fireplace meets the chimney" terminology-wise. – Ecnerwal Sep 19 at 14:15
  • There is obviously movement between the two major parts. You could seal the crack with flexible material, but could you ever match the appearance? If you used mortar, unlikely to be an exact match, plus ponting up the mortar, filling it in, requires a pretty big gap, say 1/4" to 3/8". So might be best to remove the mortar an inch or so deep, mask, then refill with new mortar. Mix and test first for color! – Old Uncle Ho Sep 19 at 16:13
  • There are a whole lot of "shoulds" going on here. The hearth should be on a 4" or thicker slab reinforced with rebar that goes under the firebox. There should be a picture showing the configuration of the firebox to the hearth as well as a picture showing the support, if visible the slab or form work on the underside, and the crack on the other side, if there is one. It needs to be determined if it is expansion from the firebox or settlement. I think so far it is expansion, and no concern except for the esthetics. – Jack Sep 19 at 17:19
  • House was built in ‘92, I’ve edited the post with a pic of the entire fireplace and other side of the hearth. I’ll try to get in the crawl space for the slab tomorrow. – DeadSysAdmin Sep 20 at 16:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.