[Cob] plastic jugs in walls?

[Henry Raduazo]

John:
	The walls in Coquille are two stories high but 6 foot 6 inch  
stories.  I do not think Coquille is in an earth quake zone so that  
may not be a consideration. Washington, DC is not an earthquake zone  
so when I figured the weight of my roof divided by the number of  
square inches in the wall I got 10 to 20 pounds per square inch, well  
within the load bearing capacity of cob.
	The rules applied to adobe are excessively conservative for cob. It  
is impossible to get the wet mud mortar to stick to dry mud bricks so  
the mortar joints form fracture lines which do not exist in cob. I  
build children's playhouses out of cob because if I built a playhouse  
in a public park from adobe people would be able to nock the bricks  
off the wall with their fist. When I build a playhouse from cob you  
need a sledge hammer to destroy the walls. Try making two a small  
test walls 4 inches thick and destroying them. There is simply no  
comparison between adobe and cob.
	Have you tried searching the CobWeb for articles about earthquakes  
Issue Twenty Winter 2005 they did a seismic test on cob and it stood  
up to level 8 on the Richter scale. Of course a test like that is a  
meaningless because the structure was built by experienced  cobbers  
who knew the building would be tested and built accordingly. My walls  
are slopped together rototiller cob made with chopped straw and  
probably not a fraction as good as cob walls built specifically to  
withstand earthquakes. Still they are impressively strong.
Ed


On Dec 10, 2009, at 10:27 PM, john fordice wrote:

> Ed,
> Based on historic seismic survival of adobe buildings, and some  
> research that was also done for adobe,  a wall height to thickness  
> ratio of 7 to 1 has good seismic survival capacity.  In the absence  
> of similar tested data for cob, I use this ratio when designing and  
> building cob walls.  At 7" thick, this would give a height limit of  
> 7x7 = 49".  What is the height of the walls you are describing?
> john fordice
>
> On Dec 10, 2009, at 7:16 PM, Henry Raduazo wrote:
>
>> 	If you are making good quality cob the wall can be as thin as 7  
>> inches. At cob cottage in Coquille they have been retying bales of  
>> straw and chain sawing them half. The half bales are stuck in the  
>> wall and this results in an insulation layer on the outside of 7  
>> inch thick cob walls. It saves tones of cob.
>> 	I just finished putting a cob wall on top of two cinderblock  
>> retaining walls 7.5 inches thick. Two 7 inch thick cob walls  
>> support 12 foot living roof 50 pounds per square foot.  They are  
>> short cob walls with a good overhang so I expect no trouble  
>> supporting the weight.
>> Ed
>> On Dec 10, 2009, at 2:46 PM, john fordice wrote:
>>
>>> Tys,
>>> I'll venture to say (without really being able to prove it) that  
>>> it will weaken the wall.  A cob wall gets it  strength by being  
>>> thick.  A structure resists forces acting on it by being made as  
>>> continuous as possible.  Making a void in the wall will create a  
>>> weak spot which compromises the continuity of the structure.    I  
>>> would not do anything which creates voids in the cob based on  
>>> this reasoning.
>>> john fordice
>>>
>>> On Dec 10, 2009, at 10:07 AM, Tys Sniffen wrote:
>>>
>>>> So, as my walls get up over 7 feet high, I'm starting to  
>>>> remember how lower
>>>> down, when I had them laying around, I would toss in the  
>>>> occasional urbanite
>>>> chunk to take up some space.
>>>>
>>>> Now I'm starting to think about tossing in some one gallon  
>>>> plastic jugs
>>>> (vinegar jugs, that are slightly thicker plastic than the common  
>>>> 1 gal milk
>>>> jug) again, to take up space, but also I'm thinking having a  
>>>> void in the
>>>> wall that size could insulation in a way, and, of course, would  
>>>> make my tall
>>>> parts a bit lighter.
>>>>
>>>> Does that sound like a bad idea to anyone?
>>>>
>>>> Tys
>>>>
>>>>
>>>>
>>>>
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>