Brick Types

[Capt. Toddy]

I picked up 200 bricks this afternoon for my WFO. They are a bit of a mix of sandstock, and pressed bricks. The pressed ones are a mix of 'smooth creams' and 'solid reds'.

Can anybody see this being a problem?

Obviously the density varies a bit and this will effect the rate of heating and cooling. What I'm more interested in is the staying power of each of these brick types. There is a wealth of knowledge on this site and there would have to be a fair amount of variety in the type of bricks that have been used. So what brick type did you use and how has it lasted?

Rod

[egalecki]

Re: Brick Types

I'm not sure we use the same terms for bricks in the US as you do in Australia. I know several people in Aus. have used the ones called "pressed reds". No idea about the others.

Neill would know. Where is Neill, anyway?

[gjbingham]

Re: Brick Types

Same here. I have no idea about the properties of Aussie bricks.

One consideration in mixing brick types is that more than likely, the bricks have different coefficients of expansion, which if true, will result in the two types of bricks expanding at different rates of speed and different amounts. The differences might possibly cause non-uniform expansion and impart additional stresses on the dome beyond those forces normally experienced in a single material build. This may or may not have some detrimental and observable effect on the oven. If it was me, I would group similar bricks together - something along the lines of the floor and first couple of courses made of one type brick and the rest of the dome made of the other.

I could be way off base on this too. Hell, I was a dentist in my previous life. I haven't studied chemistry and physics for 30 years!

Other people have mixed bricks in thier builds and written about it on this forum, but its been quite awhile since I've seen it mentioned. You might consider reviewing some of the builds older than 18 months or so to see if you can find them.

Have fun!
G.

[Capt. Toddy]

Re: Brick Types

FYI for everyone. I conducted a little experiment this arvo with the bricks that I now have. I heated three samples of bricks in the oven at 200 (c) for 2 hrs. The bricks hadn't become 'soaked' by this time but I undertook the experiment non-the-less. Attached are the results.

Rod

[bimbo]

Re: Brick Types

There have been plenty of ovens built out of pressed red so they should be fine, i have heard reference to smooth creams as well which i think have similar properties to the pressed reds, not sure about the sand stock though.

Just wondering exactly what the smooth creams are?

[Rodneyf]

Re: Brick Types

I am just starting my oven and live in Sydney. I am not familiar with "pressed reds", are they the bricks used in the federation style houses of the early
1900's? I have access to a supply of double fired face bricks from a federation house that I was going to use for my oven, these bricks are sometimes refered to as "Bondi Blues". Any thoughts would be very much appreciated.

[rosfreed]

Re: Brick Types

Re brick types:
I live in Mexico where adobe bricks are available. Can I build an oven with these?

[david s]

Re: Brick Types

Doug, you are spot on.It is the rapid heating that is the problem. We fire our ovens at around 300C/Hr which is way too fast for the refractory materials. The rapid expansion of the material close to the flame creates stress on the rest that hasn't had time to catch up. The industry standard for heating kilns safely is 100/Hr None of us has the patience to fire up that slowly. The materials you use maybe rated to withstand 1500C but that does not mean it is safe to push them at 300/Hr.
dave

[dmun]

Re: Brick Types

I live in Mexico where adobe bricks are available. Can I build an oven with these?

As far as I know, adobe is unfired clay, and ovens can built out of clay. It's probably not hard enough for the hearth, but it should be OK for the dome. Like all clay/cob ovens it must be kept absolutely dry.

The test for fired/unfired is to submerge the brick in water. If it dissolves, it's unfired.

In any case, refractory (fire) bricks make better, longer lasting ovens.

[Rodneyf]

Re: Brick Types

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]

Re: Brick Types

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]

Re: Brick Types

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]

Re: Brick Types

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,