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Incorrect mortar, mortar not setting

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  • Incorrect mortar, mortar not setting

    First a bit about myself. My name is James and i moved from Australia to the Netherlands 10 years ago. I love building and wood fired cooking.
    Now for my question.

    I have finally started building a wood fired bbq/fireplace which will later include a pizza oven. I have managed to source fire bricks and they are good. The problem that I am having is the mortar. The standard dry mix fire mortar here is full of small pieces of chamot which are to large for the gaps between the bricks. I managed to get some refractory cement but was hoping more for a grey colour mortar between the bricks instead of pitch black.
    I removed the refractory cement and tried filling the void with premixed mortar with a consistency resembling toothpaste. I was super happy with the result but after a week it still wasn't hard. In fact if I rubbed over it with water it washed away. So I thought I would try heat treating it. Some of it became hard on top but not all. And a lot of it resembled dried out or burnt toothpaste.

    My question is. Can I do anything to make the refractory cement grey instead of black.
    Can I add anything to the pre mm ix to help it become hard (portland cement?)
    Could I have played with the premix to much which resulted in it not drying? I tried wet sanding it a few times, and their was quite a few days where it rained (although the base was always covered) could humidity have affected it?
    Would it help to place a small electric fan heater under the tarp to help drying?

    Going crazy here, thanks for any replies.
    Attached Files

  • #2
    Hi James,
    that mortar is designed for high temperature furnaces or kilns and relies on its components being sintered (made permanent) at a temperature that exceeds what your oven is capable of reaching. A more suitable mortar is one that is calcium aluminate base or the homebrew mortar preferred by most builders. I think you have two choices, either live with what you have or tear down and start again. Also the floor bricks of a WFO are better left laid loose and unmortared to allow for individual thermal expansion and easier replacement should any fail.

    Kindled with zeal and fired with passion.


    • #3
      Hi Dave,
      Thank you very much for your reply.
      Very detailed and to the point. Unfortunately it was the answer I expected. I have since removed the premix as you suggested and replaced it with the homebrew.
      I should have followed the advice on this forum first instead of the salesman's. The homebrew is great!!!
      Easy to mix and apply. Sets well and dries perfect.
      I have since finished the smoke box as well.
      I have attached an updated photo.

      Greetings James


      • #4


        • #5
          I have two small questions.
          1: what size (diameter) pipe should I use and which type, double or single ( note in the future the pipe will pass through a patio roof)
          2: what would be the best way to install it?
          Bringing the pipe into the box and sealing with brick, or make a metal flange that sits on top with a pipe fitting attached (welded). Was thinking about the last one but not sure what thickness of steel to use?

          Would gladly appreciate any advice anyone can offer.
          Thanks in advance.
          Greeting James.