[Stoves] Brick making problems

[frank]

Dear brickers,

I am working with the local park service that has the task to rebuild 
the two ends of a two story building (Castro Adobe)  that cracked 
(badly) in the 1989 earthquake. I am doing my research using my 
compression tested and doing other soil tests like plasticity and 
shrinking index and percent shrinking along with chemical tests. Its a 
great project for me because they are making about 2500 bricks and when 
they uncovered the first set the other day about 70% was cracked. The 
first set was made using soil-clay from southern Calif and the rest are 
made using local material so they are hoping the rest will not crack.

The bricks are a strange size from my limited experience. They are 28" X 
14" X 4". The walls of the adobe building is 28" inches thick so they 
can use these bricks one across or turned to the side, two across.
The crack is most always in the center. One large crack completely 
breaking the brick in two. No other cracks are visible. It does not seem 
to be the result of not kneading the mud when making the brick but 
occurring during drying. I also noted the bottom of the bricks, when 
lifted up on end to dry, has a white salt layer meaning to me, the soil 
under is wicking the moisture down and drying at the contact point.

Process:
Mud poured into forms, kneaded by hand to get out air, scraped smooth 
with stick, smoothed with flat hand and form removed. Covered with paper 
on top and sides tucked in. Cover with a little soil to keep paper from 
blowing off. Watered lightly on top about three times a week. The soil 
the bricks are placed on is dry and the same type of soil the bricks are 
made of.

Any suggestions what made them crack and what to do to make them so they 
will not crack?

Thanks
Frank












-- 
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com