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Kiko Denzer on Art

[Cob] cob/straw bale sandwich wall

Henry Raduazo raduazo at
Mon Jul 21 12:58:21 CDT 2008

Robert: I have done it both ways. For a really small structure I  
prefer to put up the straw bale wall first and then build cob up  
against it. Normally I would just put a thick earth plaster on the  
outside and put a load bearing 8 inches of cob on the inside to act  
as heat storage, support and stabilizing wall.  I have found that  
when placing really wet cob up against a straw bale wall the cob  
tends to fall away from the wall during the drying process so I  
recommend that if you are doing wet cob, place dead man anchors  
between the straw bale and cob to hold the cob in place.
I have pictures if you are interested and if you have high speed  

On Jul 21, 2008, at 5:05 AM, Robert Alcock wrote:

> Hi group,
> As you may recall, we have built a small cob cabin (Snail Cabin)  
> here in
> northern Spain and we are now starting work on a larger building.
> We are looking at using a load-bearing hybrid straw-bale/cob wall
> consisting of straw bales laid on edge (35cm thick) with cob either  
> side
> (10cm interior and 5cm exterior). We plan to pour a concrete bond beam
> at first floor and roof level of this two storey, 100m2 per floor,  
> house
> and study centre.
> Does anyone on the group have experience with this "sandwich" type of
> wall construction?
> Is it better to put up the straw bale wall first, put in the bond beam
> and roof/floor beams, and then do the cob? The advantage of getting  
> the
> roof on quickly is obvious, but then I'm concerned that the straw  
> bales
> alone won't be strong enough to hold the roof.
> If the cob and straw bale go up together in parallel,  the bales  
> will be
> exposed to the weather for a lot longer (at least, the top of the  
> straw
> bale wall will be) and we get rain regularly here, even in summer.
> In this case, on the other hand, we need to think about what will  
> happen
> to the dry cob and straw bales when the load of the (green) roof and
> soil are applied - since dry cob is virtually incompressible it  
> will be
> taking the whole load of the roof on its own, without the straw bales
> helping.
> A compromise would be to build one storey of straw bale, pour the
> concrete bond beam, then apply the cob up to that height, relying  
> on the
> weather protection offered by the concrete, and also the preloading  
> that
> the concrete (+possibly roof/floor beams) provide.
> Any other guidance would be most welcome.
> Thanks a lot,
> Robert
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