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Can I use cob as a mortar for a rock house  RSS feed

 
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I was wondering if its possible to use cob as a mortar for a rock roundhouse? And then finish the inside with cob or an earthen plaster? Thanks for the help!
 
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Location: Abkhazia
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A mixture of clay and sand (cob) works well as mortar – as long as water is kept away. I have build a small brick wall with it so far and it is quite solid.

EDIT: If your stone does not wick up the water, it may take some time for each layer to dry.
 
Franak Ostapowicz
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Ok great. What do you think of the possibility of using it as a mortar for a house? Woyld the inside be weather proof if I was to use an earthen plaster as the inner walls?
 
Posts: 944
Location: Graham, Washington [Zone 7b, 47.041 Latitude] 41inches average annual rainfall, cool summer drought
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Franak Ostapowicz wrote:Ok great. What do you think of the possibility of using it as a mortar for a house? Woyld the inside be weather proof if I was to use an earthen plaster as the inner walls?


Depends on your climate. If you can expect little rain during construction and provide very good hat and boots you would probably be fine
 
Posts: 550
Location: Bendigo , Australia
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I am currently using a sloppy mud mortar to lay a double brick internal wall.
The bricks are what we call 'wire cut' with holes in the core, I just dunk the dry brick into the mixture
and lay the bricks.
The wall is very solid.
 
Franak Ostapowicz
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Well that's awesome. What is your mud mortar ratios and ingredients?
 
John C Daley
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Location: Bendigo , Australia
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Naturally occurring mixture of sand and clay with 50-50 ratio, mixed with water so its just thicker than running.
I don't mix it at all, just use it as it came from the ground.
But I did select it carefully from near a creek.
Just experiment and ask more if you need to.
 
Franak Ostapowicz
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Really cool. Is this creek on your property or do you know someone that lives on the creek? I do have a small creek that goes by my dads land. It may have what I need. Though I wonder if my subsoil has a decent enough ratio. What do you do to test it? Do you get a glob and put it in a jar with water and shake it up and when it settles you can see the different layers? Thank you so much for your help!
 
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When I built with stone, we used concrete, but I don't see any reason why you can not use cob to do it, so long as you have drainage, and a good roof protecting it from moisture in all directions.  When I lay stone, each stone is placed on the wall, so that I am sure that it works for that spot, by itself, as if it was a 'dry stone wall' (without mortar).  If it needs a small stone placed under it, so that it sits better (a 90 degree plumb angle on the inside or outside face), then add the stone and make it sit proper.  Then move the stone off the wall, and add mortar. Then lay the stone (including whatever small stone you might need to sit it right first).  The mortar is just filling in gaps, in this case, as the stone stands alone and the wall shouldn't need mortar for it's integrity if it's done this way. 
 
John C Daley
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Location: Bendigo , Australia
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Franak, unusual name, whats the background to it?
I took soil from a hole I dug 4 metres from the creek on my property.
Use the bottle test you spoke of.
Basically the mortar should be the same type of soil that you could build an earth block with.
Jf you decide ro go for cement, think about a lime mortar rather than a cement mortar.
 
Posts: 559
Location: In the woods, West Coast USA
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If you are using expansive clay it will shrink and swell even with just moisture in the air.  I live with expansive clay and it surprises me every year how much it shrinks.   The eaves on the house have to be really big to keep all rain and blowing rain off of cob and clay-based mortar. 

If you are in earthquake zones even the little temblors will cause it to crack eventually.

It just seems like there is an awful lot of maintenance, some of which may have to happen in the rain, because it starts leaking in one of those really rainy years, in which case the cob wouldn't dry in time to fix the leak.
 
Franak Ostapowicz
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Franak is one way of saying frank in Polish! I will definitely consider digging a bit and using the jar method in a few places on my dads property, that is for the advice John. And thanks for being so frank with me cristo! Ill definitely not be using clay plaster/mortar on the out side of the round house considering arkansas humidity and rainfall. I really appreciate all o' yalls help.
 
gardener
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Location: Upstate NY, zone 5
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Roberto's advice is critical, as clay mortar has no bonding ability, only sealing and stabilizing. Your stone walls must be able to stand by themselves, and resist any stress or shaking they may be exposed to.
 
Franak Ostapowicz
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how thick do the rock walls need to be and how can i insulate the inside? wiring in between rock and earthen plaster?
 
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