What mix and sand\cement ratio's should I use for replacing a chimney stack flaunching?

I've seen suggestions to add some sharp sand to the building sand, and other suggestions to add lime or plasticizer or even PVA glue, but without an explanation of why I don't want to risk it!

  • I would use fire brick mortar it can handle the heat and can be purchased in bags or premixed buckets. I like the bags because they can be sealed and last forever if kept dry. once the buckets are opened they always tend to dry out.
    – Ed Beal
    Feb 26, 2016 at 14:31
  • 1
    "Flaunching" is an excellent word, BTW. Feb 27, 2016 at 3:27

1 Answer 1


Nobody answered so I went with:

  • 2 parts sharp sand
  • 1 part soft/builders sand
  • 1 part cement

Seemed to work ok.

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