Cob: sandy soil

[dtebb]

>    Thanks for all the info. I'm building it a 15 ft round with flat on
>one side  for my windows. Sort of a half moon shape i guess. I'd like to
>do just a shed roof cuz it seems  easiest we got lucky and got a bunch of
>windows free.   They are in great shape and all four have double pane
>windows in them that  work! They are pretty big and so that's what
>determined  the shape of the house plans. I'd like to have already gotten
>started because the  weather has been so great here in Minnesota!! It's
>been so warm and wonderful out. I think it will take quite a while to dry
>however  so I'm thinking I might need to build the roof first so we can
>move in with semi  wet walls. It will be getting very very cold  soooooon!
>My clay that I had brought in gets extremely hard,  not really crumbly at
>all.  Maybe I just got sandy clay?? I was thinking of just using it
>with a very small  amount of my sandy soil like 70%clay 30% soil and
>mixing with either a cement  mixer or a bobcat. Anyone have experience
>with either?  Sara

Hi Sara,

I have used both a mortar mixer and bobcat. First, I don't think you want
to use a cement mixer. They work very differently and usually cob is mixed
in a mortar mixer. I found the mortar mixer to work very well and fast, but
that was after screening the clay to fairly small pieces. If the clay
remains hard and in big clumps, it may not mix so easy, but rather the clay
may ball up into baseball size clumps and not mix. You also will want to
screen out as many of the larger rocks as possible as they sometimes jam up
the paddles and possibly damage the mixer. I also think that different clay
will work differently. I had nice soft clay. Using alot of water will help
mix up the clay but you will have to let the cob dry out for a few days
perhaps before using it. As for a bobcat, we used one one day. It did a
reasonable job at mixing, but you will want to mix your pile on a hard
surface, preferably a cement slab. we mixed on fairly soft ground and dug
up lots of silty crap into our nice mix. A bobcat does work well, but it is
noisy and smelly. We were at it for about 2 or 3 hours and produced a large
picknick table size pile of cob. It kept alot of us cobbing for a few days.

Ian Marcuse