[Cob] Re: Screening clay for floors & plasters

[ocean]

Hey Ed, Amanda, all,

I've had no trouble making and applying volumes and volumes of 
plaster/floor mix (200 linear feet of wall, 600 sq. ft. of floor) with 
a very simple procedure:

1. Whip beautiful red clay in a 55 gallon drum with enough water to 
cover, resulting in a nice runny clay slip.  I use a 1/2" drill and 
drywall "beater" to whip the slip.

2. Pour the clay through a 1/4" mesh (hardware cloth), screeding a bit 
back & forth with a 2x4 block.

3. I don't do a second screening, just mix this slip with river sand, 
ratio is 3:1 (sand to clay) in an Imer electric cement mixer for 
plaster.  For floor finish I'd go with a higher ration - 5:1 or more 
(Ianto told me 7:1 for his floors !!)  I don't worry about rocks in my 
slip, since the sand also has small rocks approaching 1/8-1/4".

4. I spray in enough water to the mixer to make sure the clay slip 
completely coats all the sand particles.  Then I add chopped straw 
which has been screened with a 1/2" mesh.  The straw absorbs enough of 
the water in the clay/sand to make a nice consistency.

5. The trick to getting a smooth finish is in the floating after the 
plaster/floor finish is applied.  "Floating" brings the fines up to the 
surface, and forces all the bigger stuff (rocks, chunks of unmixed 
clay, etc.) deeper down, resulting in a very beautiful smooth wall or 
floor.  On walls we float with stainless steel Japanese trowels, which 
I love!  For the floor a nice cement float works well.

Good luck, but don't worry about screening out those little sharp 
rocks.  I've never had the patience for an 1/8" screen, though for very 
fine sculpture work, Kiko uses very fine sand and clay, plus grass-fed 
cow manure.  He has some beautiful bas relief sculptures on exhibit at 
Intabas, you can see pictures of his sculptures on our website:  
http://www.intabas.com

Happy "Cob"-mas!

Ocean
Intaba's Restaurant, Corvallis, Oregon
http://www.intabas.com
Ahimsa Sanctuary for Peacemaking and Sustainable Living, Philomath, 
Oregon
http://www.peacemaking.org


On Dec 9, 2004, at 10:29 AM, Amanda Peck wrote:

> I've run it through the--half-inch--screen as dry as possible--not 
> very, given that the clay pile is outside--which means that we 
> basically extruded bits through the screen, letting the easy stuff go 
> on down (into a garbage can) and sometimes putting the bigger pieces 
> away for later consideration
>
> But I'm using galvanized wire mesh, the kind you use for rabbit cages. 
>  Not all that likely to break, in the two-foot square we were using, 
> in other words.
>
> And there's plenty left in the garbage can after we did a 100sf floor 
> at about an inch and a quarter deep in one step.  The mixture WAS less 
> than a quarter clay.  We were able to use one clay, three sand, and 
> maybe a bucket of wood shavings, no idea what you're having to use.
>
> But seems like some people are getting themselves SOME powder/dry 
> clay, and mixing the rest into a slip, pouring that through their 
> screen, drying it out in the final floor mixture with sand and their 
> clay powder, and wood chips or sawdust or whatever.  I guess you'd 
> want to add a lot of water, mix a lot, let it stand maybe overnight 
> and take off the nearly pure water that accumulates on top, pour the 
> next layer through that or even a finer screen, with or without the 
> stones that have accumulated on the bottom.  Using the ubiquitous 
> 5-gallon buckets--3-gallon if I can find them and they're not too much 
> more than the 5  (they sell fewer of them).
>
> A third way, (if you've got one of those concrete mixing tubs or a 
> shallow rubber-like tub and enough wire mesh to make a basket to fit 
> it,)  might be to lay the mesh basket in the tub, put as dry as 
> possible clay in there. pound with a mallet, then lift the basket, 
> shake out all the small stuff, pour the now sifted contents of the tub 
> into something else, repeat.  (I really have pounded very dry clay in 
> a tub, poured out what will go through the mesh, and repeated)
>
> But take care of your hands!  Pure clay is pretty sterile, but just 
> dirt isn't, and the particular composition of the soil bacteria varies 
> wildly, from stuff that pediatricians wish that more toddlers were 
> exposed to, to mildly stimulate their immune system, on.
>
> Ed wrote:
>
>     I am having a problem processing enough clay for a floor finish.
>     The first step is to wet it and mix it with a power mixer then I 
> push it
> through 1/2 inch screen. This gives me a tapioca-like mixture of clay 
> tapioca
> balls mixed with a few very sharp quarts rocks.
>     The next step is add more water, mix it again and push it through a
> window screen. This is where the problem occurs. When I place an 
> aluminum or nylon
> screen on top of the 1/2 inch screen and try pushing the clay through 
> it is a
> very slow process. I cut up my right hand Tuesday, my left hand 
> Wednesday just
> making one batch a day, and I am not looking forward to five more 
> batches
> needed to finish. I can wear dishwashing gloves or a wooden block 
> taped to my
> hand to protect it from the sharp rocks, but if I use more force to 
> speed up the
> process it tears the window screen.
>     Today I am going to try 1/4 inch screen and then two layers of 1/4 
> inch
> screen set at a 45 degree angle with a power mix between steps to get 
> rid of
> the tapiocas. This stuff is tough enough to take lots of force. Then I 
> when I
> get to the window screen it is my hope that most of the sharp rocks 
> will be gone
> and I can use a little more force.
>     If this does not work I am not sure what to do. I am slated to 
> help Chris
> do his floor next. He wants the same nice red clay as I am using for 
> my floor
> and his floor is twice the size of mine.
>     I tried finding a supplier for stainless steel screen but cannot 
> seem to
> find anyone who wants to sell small quantities.
>     Does anyone have ideas? Someone must have had this problem before 
> me.
> Ed
>
>
>
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