Cob: Test Bricks

Sat Nov 9 18:26:20 CST 2002

I am new here [and new to cob] and do not know what all subjects have been covered, but my interest has been piqued by the recent posts concerning the mixture to use in making cob.

After doing some tests on the soil on my property I found that it was anywhere from 80-95% sand, according to where I collected the sample, with the remainder being silt. There was no clay mixed in with the soil, but if I dug down anywhere from 6 inches to 1 foot I found solid red clay.

I made some test bricks using the soil and the red clay in three different ratios and found that 25% clay and 75% soil was a bad mixture and the bricks made from it crumbled easily.

The two other ratios that I tried were 50/50 clay/soil and 75/25 clay/soil. 

The 50/50 did not crack in the drop test until 3 feet above the ground, and it broke at 5 feet above the ground. 

The 75/25 cracked at 5 feet above the ground and broke at 7 feet above the ground.

With what little I know it seems that the 75/50 ratio is the best and should be used in any cob that I make from my land, but reading here and on other sites it seems that 75% clay is too high.

Am I missing something here? Would someone please fill me in on whether or not I should use the 75/25 clay/soil mixture. It would seem to me that I should since it passed the drop test so well, but looks can sometimes be deceiving and I would like to know if I am missing something.

Thanks,

Kim
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<DIV><FONT face=Arial size=2>I am new here [and new to cob] and do not know what 
all subjects have been covered, but my interest has been piqued by the recent 
posts concerning the mixture to use in making cob.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>After doing some tests on the soil on my property I 
found that it was anywhere from 80-95% sand, according to where I collected the 
sample, with the remainder being silt. There was no clay mixed in with the 
soil, but if I dug down anywhere from 6 inches to 1 foot I found solid red 
clay.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I made some test bricks using the soil and the red 
clay in three different ratios and found that 25% clay and 75% soil 
was a bad mixture and the bricks made from it crumbled easily.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The two other ratios that I tried were 50/50 
clay/soil and 75/25 clay/soil. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The 50/50 did not crack in the drop test until 3 
feet above the ground, and it broke at 5 feet above the ground. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The 75/25 cracked at 5 feet above the ground and 
broke at 7 feet above the ground.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>With what little I know it seems that the 75/50 
ratio is the best and should be used in any cob that I make from my land, but 
reading here and on other sites it seems that 75% clay is too high.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Am I missing something here? Would someone please 
fill me in on whether or not I should use the 75/25 clay/soil mixture. It would 
seem to me that I should since it passed the drop test so well, but looks can 
sometimes be deceiving and I would like to know if I am missing 
something.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Thanks,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Kim</FONT></DIV></BODY></HTML>

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