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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.