Making terra cotta bricks

[Magnolia Mud Research]

Or you can just use several layers of newsprint.  The top layers stick to the bricks, the bottom layers stick to the board, and middle layers are free to move  and peel away when the bricks are lifted.  Cardboard and tarpaper should also work.  

LT

[Peter Angel]

Quick update.

I tried 3 layers of newspaper at the bottom of the brick but it buckled and wrinkled badly when it got wet and it left a deep texture into the bottom of the brick that I had to smooth out. No big deal but it was one addition step. 

Then I tried 1 layer of aluminium foil at the bottom of the brick. Foil has 2 sides. A textured side and a smooth side. I used the smooth side. It worked perfectly! Peeled off cleanly.

Pete

 

[Peter Angel]

Hello all,

This failed badly.

The thick bricks (2.5" - 3") cracked when I put them in the sun.

I did some research. Big cracks happen when you don't use enough sand. 

I found the following recipe on Wikipedia:

Normally, bricks contain the following ingredients:^[15]

1. Silica (sand) – 50% to 60% by weight
2. Alumina (clay) – 20% to 30% by weight
3. Lime – 2 to 5% by weight
4. Iron oxide – ≤ 7% by weight
5. Magnesia – less than 1% by weight

Can some please tell me what I would use for lime? 

Getting closer!

Pete

 

[tinbucket]

I would say skip the lime. I'm thinking the recipe above was for bricks that were not fired/not ceramic and rather aggregate cemented together (like concrete). Large chunks of lime are undesirable in ceramics (I believe they absorb moisture after being fired, expand, and create holes in the fired surface - search lime pop out). I'm sorry to hear about your cracked bricks, I would try 50/50 clay and coarse sand (40 or lower mesh). I would try drying a few in direct sunlight just to see how far you can push the drying process - or you could dry them more delicately and flip them periodically.