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]

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]

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]

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]

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]

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

[Karangi Dude]

Hey Capt. Toddy,
All bricks will expand when heated and at different rates.
To me it is not the expansion but the thermal shock that is the issue. I have read Russel Jeavons Book on WFO he says that solid reds are fine as thay are fired at 1200c but it is the cooling down and then reheating that's the problem. Russel runs a restaurant so I would imagine his ovens never completley cool down. I used all fire bricks to avoid any thermal shock problems, if you don't want to go down that track at least use fire bricks for the hearth and if that is still a problem use only two kinds of bricks, one for the hearth and one for the dome/walls don't mix them up. Solid reds and clay bricks are much better than any sandstock I would only use sandstock bricks for an enclosure. Your test of heating the bricks does not prove to much as you heated the bricks pretty slowly, did you know that a flame tip is in the 700/800c range so when you light you oven the area that has the flame contact is going to heat up rapidly and the rest of the oven is going to remain a lot cooler this where cracking will occur.

Cheers Doug

[david s]

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]

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.