Cob: RE: RE: CEBs

[Michael Fitzgerald]

Hiallyall

Charmaine: Yes that is the Cinva Ram that I got from Fernco Metals in New
Mexico. They where pretty fast and the machine is very nice. I had a
boilermaker friend who is the welding messiah look at it and he was
impressed with the price and workmanship. I am very happy so far with my
purchase.

DJ: I am pretty much sticking with the suggestions in the BASIN publications
as I have spent alot of my life reinventing the wheel. I read both volumes
cover to cover and they seem to be well researched and based on practical
experience. Soooooo, no I don't think the block should be placed in a wall
to cure. They are very fragile when they first come out of the mold, and the
publication suggests not moving them for 2 days. That's about right. I also
have been hosing them down every day for the first few days and am
constantly amazed at how much water they soak up. On the third day I have
been stacking them. They are still not anywhere near full strength at that
point and I had some crack due to improper stacking and handling. Some of
the first have been curing for a week now and don't soak up as much water
and are noticeably harder. I have put a few down  on uneven ground and walk
over them every chance that I get and they seem to be taking foot traffic.
The publication recommends a two week cure for blocks made with a cement
stabilizer and 30 days for those made with lime. As for the mortar. I have
also seen sites where it was suggested to use a thin mortar. The basin
publication suggests a standard masonry mortar composed of sand, lime and
cement and to treat it with a typical struck joint. I think this is the way
to go with a hand operated machine like mine because it is difficult to make
all your blocks to within a 1/4 to 3/8" tolerance on the thickness. My
tolerances may improve as I get better at it. We shall see.

Bill: My recipe comes from the BASIN publications. A shake bottle test of my
soil shows approximately 20% clay, with about 40% sand, and the rest being a
fine silt and a good amount of pebbles etc. I came across some references in
bricklaying books to soilcrete roads and patios. They recommend a minimum
15% Portland cement to soil ratio. The BASIN publications recommend a 5%
ratio for CEBs. However they also make reference to 10% blocks used below
grade and in situations such as water tanks. I am trying to convince a very
tolerant but somewhat reticent spouse as to the architectural soundness of
CEBs. Consequently I have decided to run with a 10% mixture for the first
few projects. This ratio lightens the color of the brick and I am slightly
disappointed to lose the pink hue that I was getting when I was making blox
with straight soil and no stabilizer. However, Home Depot is selling blocks
half the size of mine for a $1.25 and they call this color "Carrington
Buff". My wife rests easier now that she can tell the "normals", "We decided
to go with Carrington Buff!" I am getting 50 blocks per bag of cement and
inputs are costing about 14 cents per block without factoring in the cost of
the machine. The biggest factor I find in making block is how well you
screen the soil. The BASIN publications suggest starting with screened  and
dry soil. Having dry soil makes mixing the cement into it  alot easier and
helps to achieve consistent product.

Which brings me to some musings on machine mixing cob. Has anybody tried
mixing straw and dried screened soil and then just adding water? The BASIN
publications suggest that soil could be prepared on a large scale with
impact mills and pulverizers. The idea is to get the lumps of clay as small
as possible so that they bind well with the straw and sand in the mix. It
just seems to me that bringing clay and straw together would be easier when
they are both dry. I might try it this weekend if nobody writes to say
they've tried it and it doesn't work.

Happy Independence Day one and all.
May God bless us all.
May God bless our Libyan Brothers
May God protect those who build their houses from earth.
May God give our President even a little bit of sense.

Michael Fitzgerald
Anthropologist/Woodcarver/Puppetmaker