[Cob] a cob bathtub

[Amanda Peck]

May have written it wrong, but I did know that you have to have clay, and 
preferably something on the order of straw wood chips and/or sawdust, in 
your floor mix.  What I thought was in question was the amount of oil.  And 
I figured that everything would stay in suspension better if the oil was 
mixed well with the sand to start with, then with the more or less powdered 
clay, then with water.

I hadn't thought about making (unused!) kitty litter mayonnaise, with what 
sounds like quite a bit of oil.  Although it ought to give you a better 
waterproof finish as a floor.  Or, for pete's sake, a bathtub.

I think a couple of people have mentioned adding oil to their floor mix.  I 
didn't do it.  I put in a one-coat inch and a quarter (35 mm?) floor. 
pounded in well over maybe 8" (somewhere around 200mm) of well-tamped and 
well-drained gravel and given a nice trowel finish.  The only cracks seemed 
to be where we didn't pound it in well enough--it sounded hollow after it 
dried, just before I walked on it and caused the cracks!  I still haven't 
finished it, although I did fix the hollow places.

It wouldn't have occurred to me to put a soft rock-proof layer between the 
rock and the floor mixture.

...............
Shannon wrote (snipped)
In a separate bucket you will want
to make an emulsion by mixing one part bentonite clay (I bought a box of
of generic clumping cat litter which listed only bentonite clay in it's
list of ingredients), six parts water, and eight parts oil (this was off
the shelf boiled linseed oil from the local hardware store).  Mix this
thoroughly, it should end up with a consistency similar to mayonaise,
probably will do better if after you mix it, let is sit overnight, then
mix it again.  Finally, mix your sand and clay together, and in place of
additional water, add the emulsion to get your usual pre-straw cob working
consistency, and finally add the straw.  I mixed this in a five gallon
bucket, making batches of about three gallons at a time (using a heavy
stick to do the mixing).  Keep in mind this is intended to be a finish
coat, so it is typically going to be less than an inch thick and you
won't need that much, three gallons would cover six to twelve square feet
depending on the thickness.  If you dry this quickly (as I did, using a
fan), expect cracking, though of course you can fill in the small cracks
with a fine mix.  Once this is dry it is usable and much more durable than
straight cob, but still somewhat fragile, ultimately it will still require
multiple coats of linseed oil to finish it.

 > Using it on top is easier, and you probably want to do it this way even 
if
 > you did use oil in the mix.  Just wipe it on.  Mixed with mineral spirits 
if
 > you have it.  Let dry, repeat--probably three coats in all.  Then leave 
out
 > in the rain for a couple of months!
[snip]

The way I was originally taught this was to use uncut linseed oil for the
first coat, then add thinner to linseed oil in progressively greater
quantities to the succeeding coats (seven was the recommended number as I
recall).  A number of people I know have just been using the linseed oil
without thinners in multiple coats.  I think one person used thinner in
all their coats in order to get deeper penetration into the floor.  The
basic rule in applying linseed oil to anything is to apply it, give it
some time to absorb into the surface (ten minutes comes to mind), then
wipe off ALL the excess (a single drop of linseed oil left standing on
the surface will not only take forever to dry, but will create a gummy
mess if you step on it).  With a floor, you can just work slowly,
and migrate the excess from the treated areas to the untreated areas,
supplementing with more linseed oil as you go.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
                       |    Embedded Systems, Real-time, Device Drivers
Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications
    or: (541) 929-4089 |                  www.deatech.com