[Stoves] Brick making problems

[frank]

Dear Crispin, David and others,
The bricks seem to be cracking starting from the surface.  Not from the 
bottom as I would have expected.  The center -bottom is still very wet. 
The ground under the brick is very wet with a 'seal'  at the bottom of 
the brick. The brick has been covered with kraft paper on top and sides. 
Straw was added to the mix and broke like someone cut it with a knife.  
Even the newer bricks made of local material are cracking in large 
numbers. The bricks only shrunk about 0.5 inches on all sides. We have 
no rain and only mild temperature.  Water is hosed onto the kraft paper 
three time a week (?) but I don't think it penetrates to the brick. They 
crack before they are dry enough to stand up.

I brought back a brick to the lab and plan to do a pattern analysis of 
the moisture. 

I wonder about:
1) when making the bricks to place them on top of the kraft paper or, 
perhaps sheets of plastic so they slide ?
2) using cloth like burlap on top that will soak up the water?
3) add calcium like gypsum or lime to make the particles more sticky and 
reduce shrinkage (resulting in a less dense brick).


something like that

Thanks
Frank




Crispin Pemberton-Pigott wrote:

>Dear Frank
>
>This crack is an example of adhesion of the brick to the support underneath.
>It is interesting that you did not mention any other significant cracks.
>The brick is so big and so soft that the friction between the bottom and the
>surface it is sitting on is enough to prevent the brick shrinking normally
>(and get shorter).
>
>Pouring a mud mix is a way to just about guarantee significant shrinking.
>Try to reduce the water content to a paste instead of wet enough to be 'slop
>moulded' as we call it.
>
>You can a) add chopped straw/grass to give it more strength so that when it
>shrinks it will pull the dead weight of the brick ends towards each other
>instead of breaking, or b) put something underneath so it can slide (like a
>bed of sand) or c) as soon as it can be turned, put it on edge to dry, and
>stack them near each other.
>
>It sounds like they are not being used to keep each other damp as they dry
>very slowly.  There is a good example of drying slowly at
>http://www.newdawnengineering.com/largeimage.php?imagename=tbric015.jpg&retu
>rnpath=/website/brickandtile/tbrick/index.php
>
>You bricks sound too big to stack on end but don't rule it out. Perhaps
>stacked against a strong wall. If you can pick it up (barely) and get it off
>the ground it will be less likely to break as the drying progresses.
>
>Good luck!
>Crispin
>
>
>-----Original Message-----
>From: stoves-bounces at listserv.repp.org
>[mailto:stoves-bounces at listserv.repp.org] On Behalf Of frank
>Sent: August 13, 2007 9:23 PM
>To: Discussion of biomass cooking stoves
>Subject: [Stoves] Brick making problems
>
>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. 
>
>
>
>
>  
>

-- 
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