[Cob] Re: Bathroom / kitchen tile in a cob house

[Barbara Roemer & Glenn Miller]

Paul inquired a couple of days ago about bathroom tiles:

"Do any list members
have experience of using tile on cob walls? How to stick them on - lime
putty? mud/dung plaster?"

Charmaine replied with a link to Emerald Earth's beautiful greenhouse
shower, which prompted me to ask Michael Smith, long-time resident there and
fine natural builder, about their construction process with the shower.
(There was also some question of a leak.)

Michael graciously replied,

"We did initially have some moisture problems in our sauna due to a
flashing problem in the ceiling. That had nothing to do with the cob
or tile.

This is how we did our tile shower: First we painted the cob surface
with waterglass (probably completely superfluous), then screwed
expanded metal lath to the cob surface, then stuck on the tile with
thinset mixed with a synthetic waterproofing additive, then grouted
with conventional grout, then sealed the grout with a tile sealer.
Lots of synthetic materials, but no problems at all to date."

In my own shower, I used the traditional (higher embodied energy) approach
with thin-set, but in the bathroom earthen floor, I installed pads of tile
at the tub side and the back door so areas of high and potentially wet use
would be more protected.  The travertine tile was practically free and too
thin for an application where if the earth beneath it subsided or shifted
just a bit, it would crack.  I reserved the to-be-tiled areas with pieces of
scrap plywood when we did the floor.  Then I put a thin layer of thin-set as
a bed for the tile, laid the tile, and grouted it with earth floor mix so
the finish level just matches that of the earthen floor.  Then I oiled the
whole thing.  Water still beads up on it after four years.

If Minke builds sinks of oiled cob, probably a shower pan would work, too,
but I was too timid to try it.  The vertical surfaces are less a problem
than water collecting and sitting on the horizontal ones.  Waterglass is
potassium silicate, available from chemical supply houses or pharmacies or
some hardware stores.

For those of you who are interested in tracking it down, Bill Steen had some
posts about lime plaster in showers at their place outside of Tucson, on the
SB R Us list (Yahoo).  They've held up beautifully, but I think the pans
were concrete.