Expansion issues??

[mrpottsmeister]

So, after 12months my build looks like this (see below)

[mrpottsmeister]

[mrpottsmeister]

I now have the materials to bring the recess up to finished oven floor level consisting of, (from the top down) 25mm fire brick, 40mm Calcium silicate board then approx 100mm vermicrete down to the concrete base. What I'm concerned about is, as I am building a square fireback floor, to fit the redbrick perimeter, should I fit the firebricks tight to the red bricks or should I leave a gap to allow for expansion(10mm???) and if so should I fill said gap with a refactory mastic?

Also as I have decided against building a 'keyhole' shape oven floor, intending instead to build my dome straight onto a flat firebrick base, I am concerned about the first course of dome bricks cracking away from its base due to heat expansion, is there anything I can do to counteract this or am I worrying too much??

Hope this makes sense

All help greatly appreciated

Thanks Matt

[downunderdave]

I think you're worrying too much. It makes little difference whether the walls of your oven are beside the firebrick floor or on top of the firebrick floor. The only problem of building on top of the floor is that it makes it almost impossible to remove a floor brick once you've built over it. Any floor brick replacement will probably only be done by your grandchildren and should only be needed in the bricks in the middle. You must make sure that there is insulation under the walls though.

[mrpottsmeister]

Cheers Dave

That has put my mind at rest,

Turns out I've miscounted My my firebrick and don't have enough to goright to the edge, would it be acceptable to use terracotta tiles around the perimeter so my dome wall sits on them? I guess this will help weatherproof the areas not covered by the dome!?

I have noticed On a few posts that people have wrapped their calsil board in tinfoil in case water gets in, what are your thoughts on this, also, as I have two. . 1m x0.5m boards am I OK to simply butt these together, or do I need to join them somehow?

One last question, can I use vermicrete on top of, as well as under, my calsil board, should I need to pack my terracotta tiles level with my firebrick?

[downunderdave]

Apr 5, 2017 12:48:22 GMT mrpottsmeister said:

Cheers Dave

That has put my mind at rest,

Turns out I've miscounted My my firebrick and don't have enough to goright to the edge, would it be acceptable to use terracotta tiles around the perimeter so my dome wall sits on them? I guess this will help weatherproof the areas not covered by the dome!?

I have noticed On a few posts that people have wrapped their calsil board in tinfoil in case water gets in, what are your thoughts on this, also, as I have two. . 1m x0.5m boards am I OK to simply butt these together, or do I need to join them somehow?

One last question, can I use vermicrete on top of, as well as under, my calsil board, should I need to pack my terracotta tiles level with my firebrick?

Re the terra cotta tiles, they may or may not work, because you don't know the thermal shock characteristics of the clay body used and the tiles are not designed for this application, however if I were in your position I think I'd give it a shot, but the worst that would happen is that they may crack a bit which just leaves you with more pieces and they'll be on the outer part of the oven floor anyhow. The floor bricks are generally not mortared to allow for expansion and movement as some will get hotter and expand at a different rate.

Re the use of foil, just remember that if used to stop water getting in, it also stops water getting out. I like to seal between the floor insulation and the supporting slab, to stop rising damp from the stand, but also have one or two holes through the supporting slab through which moisture can escape.

Re expansion gaps remember that the inner parts of the oven are expanding while the outer shell and decorative arch remain cool. This sets up enormous stress and often results in cracks around the outer dome shell near the outer decorative arch. So designing it in such a way that the inner oven parts can expand freely inside the outer parts is a good solution.

However, as they say, "there are two kinds of ovens, those with cracks and those with oven owners who lie about their ovens not having cracks".

You can use vermicrete beside, under or over the cal sil, but seal over it with render if it's exposed to the weather.

Yes, you should pack the terra cotta tiles so they are level with the firebricks, homebrew should be good for this.

[mrpottsmeister]

Many thanks Dave!!

Will post pictures once the next phase is completed this weekend!