Brick Types

[Rodneyf]

Just an update to this thread, I finished my oven a little under 2 yrs ago and have used it about 15 times with no sign of brick spalling or cracking so far.
I have got 2 hairline cracks on 2 mortar joints but they have not proved to be a problem and there is no heat on the out side of the dome at these 2 points so I do not think the bricks have failed, it is simply a crack in the mortar joint.

[azpizzanut]

Hello Capt. Toddy,

Using a little "Pizza Oven Builder Logic" you might consider the heaviest bricks of standard size for the dome and hearth since they will hold heat better than a lighter, less dense brick. If the brick doesn't dissolve in water then it would be a good bet. Use the questionable bricks for less heat sensitive elements of your build.

If you have very light bricks then you could consider them for insulation under the hearth. Many Aussie and Kiwi builders use Hebel under the hearth with fair to good results. I would augment any questionable insulating brick with a layer of perlite and Portland or vermiculite and Portland in a 5:1 (up to 10:1) mix over the top of those bricks, by 2-3 inches. You don't actually "pour" this mix but shovel it in place and tamp very lightly to push it into the form. You don't want it to be so wet that water carries away the Portland cement. Just use an angle iron or piece of lumber to level the surface. It doesn't trowel or finish like concrete. Use sand and clay 50/50 for a leveling paste, 1/4" thick, for your hearth.

Best of luck,

Cheers,

[david s]

Bob,
A 10:1 vermicrete mix is too weak to be used under the floor. You need 5:1
A 10:1 mix is ok for insulating the dome where the cement content is only needed to hold the mix together.
I'd hate to see someone try and support the huge weight of an oven with a crumbly 10:1 mix and find it fails.

[azpizzanut]

Hi Capt. Toddy, David S,

David, thanks for your concern about the vermicrete mix for the hearth. The recommendation is for 5:1. A mix of up to 10:1 can be used elsewhere, such as the dome, as you noted, but I didn't communicate it well. Thanks for pointing that out.

Cheers,