[Cob] oil and cob, floors, too

[Amanda Peck]

The lime finish is harder than a cob/earthen plaster finish, which might or 
might not make it the best choice for INSIDE window sills (especially after 
a century or so!), alternatives would be wood, or stone, or.....  Not much 
in the way of outside sills is what the books show, I think.  mostly rounded 
so that water won't sit there.   A good seal between your window glazing and 
the cob, so water doesn't drip down into your wall.

I've been bad about putting links in.  here's the Dancing Rabbit flooring 
saga.  Notice how they're pounding.  I think I'd greatly prefer not to put a 
layer of waterproof stuff down, at least partly because I'd be afraid of 
movement or hollow places as the floor went on.  Sand on both sides might 
make it OK, apparently it did for them.

http://www.dancingrabbit.org/newsletter/Newsletter0701-floors.html

"As dry as possible" and "a couple of handfuls" of straw/manure raise 
question marks for me on Dorethy's floor.  Did you pack the 2nd and 3d 
layers in as well as the first?  We put a layer of hay (not straw season!!) 
which we changed a couple of times on the freshly done floor to slow down 
drying time and prevent cracking.  Don't know if Dorethy did that, not 
absolutely sure we needed to, but that I'll do again, it's easy enough.

Linseed oil dries nicely.  Boiled dries a lot faster than the raw, say the 
people who finish furniture.  I did test with boiled, coated some wood with 
boiled.  The last coat may well be visible on top of the original surface, 
if my brick is any indication. of how it works.  No problems with stickiness 
after it dries, but don't paint yourself into a corner.  (Boiling linseed 
oil is apparently a "don't try this at home" thing, by the way.  It's been 
known to explode)

Cracks ARE caused by shrinkage (I haven't mentioned the time I tried to do 
lime plaster without any sand?  That was SPECTACULAR!) and/or hollow places 
that you can hear by the time it dries.

On my floor we tamped a fairly deep gravel layer (8" or more above ground 
level, two sets of drains on the outside, which was why I thought we could 
do without waterproofing) like mad, it settled a couple of inches, even 
after tamping lower layers.   I put in a lot of expansion joints, we used 
what looks like a good cob mix for us (but not everybody else!!), 3:1 
sand/clay, mixed, watered pretty heavily, then dried it out with at least 
half of a bucket of wood chips, usually more, instead of straw.  The 
"mud-pie queen of Oklahoma" supervised, we stomped until the stuff rolled 
clean from the tarp, didn't pound every place we needed to into the floor.  
Oops!  I know I'm responsible for at least one of those places!

This worked fine, except for the hollow places.  The "expansion joints" may 
have been necessary, but they were a LOT of trouble.  A man who had done a 
lot of large-scale pottery told me that a four feet on a side sample is 
really good for shrinkage tests.  I didn't want to do those, so....  I think 
next time I'll do a test.

Even with the oil, you CAN cut out down, probably one layer, a couple of 
inches on each side of your cracks, re-do them.  It should dry faster.  You 
may be able to wash the cob mix off of the oiled surface, I'd try for as you 
do it.

Remember that the outside finishes of those lovely African houses are 
renewed every year or so, for all I know they change designs while they're 
at it.
.............
Kim wrote (also a reply to Dorethy)

Having read the last few posts about sealing cob I am wondering--if one were 
to put extra thick lime plaster [that doesn't have oil added to the mixture] 
on the outside window sills, could some applications of oil then be used 
after applying the plaster to help further seal them as long as it is only 
put on the top surface of the sills--or would putting oil on lime plaster be 
redundant?

And with linseed oil on a cob couch or bench--would not the oil get on your 
clothes?

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