lesley alexander on thu 22 oct 09
Never done architectural tiles but may make some for a friend.... for =3D
the wall behind a wood-firing stove. This would involve subtle, unfired =3D
textured tiles; it will be a strawbale, plastered home. I know we have =3D
to be careful to know shrinkage and also, if we add outside work, =3D
adsorption. Ron Roy has recommended that it not be capable or more than =3D
1.5% adsorption. There seem to be clays that do that, although it would =3D
of course require testing.=3D20
This is from an entry by Ron Roy some years back:
I know that having the absorption - after boiling a dry sample for 2 =3D
hours
- under 3% will ensure enough vitrification so the ware will not leak or
absorb enough water to be a problem. So I try to keep each body between =3D
1
and 1.5 % absorption and specify that it be fired at one cone. =3D
Porcelains
are kept as close to 0% as possible. Ron Roy
To find the absorption rate, subtract the saturated weight (fired, =3D
soaked) from the dry weight.=3D20
Divide the difference by the dry weight. For example, let's say a pot =3D
weighed 0.75 pounds after
it was fired to maturity. After boiling, it weighed 0.8 pounds. The =3D
difference is 0.05.=3D20
Dividing 0.05 by 0.75, we get 0.067, or an absorption rate of 6.7%. (the =
=3D
net)
Weigh the just fired clay as it comes from the kiln - before any
atmospheric moisture has a chance to get in - or wrap it up very well so =
=3D
it
stays the same.
I boil for two hours - which may be the same as soaking over night - =3D
what
ever you do don't change unless you do a comparison test to see if the =3D
two
techniques produce the same % absorption.
Does anyone have any suggestions or references about all this process? =3D
The more info the better.....
Lesley Alexander
Stephani Stephenson on sat 24 oct 09
Leslie. just a few thoughts. As always, do your own checking and take ev=
=3D
erything anyone=3D20
says as general suggestion only.
In my humble opinion,It is OK for wall tiles for an interior wall/stove s=
=3D
urround to have a=3D20
higher absorption rate. wall tiles for stove surrounds are not drinking v=
=3D
essels.
these are not exterior tiles, pool or tub tiles or floor tiles. Their pr=
=3D
imary job is not to=3D20
keep water out,or hold water in.
their primary job is to provide a stove surround which is non combustibl=
=3D
e, attractive,=3D20
easy to clean, and which may, to some degree, act as a heat shield.
I would think in terms of whether your clay body and surface will meet th=
=3D
e needs of the=3D20
application. in fact, thinset mortar may not easily adhere to imperviou=
=3D
s or even vitreous=3D20
tiles.
in fact the thinset mortar, when sured, also acts as a moisture barrier. =
=3D
Other moisture=3D20
barriers such as plastics, as well as hear barriers such as tinfoil are s=
=3D
ometimes put into=3D20
tiled walls where appropriate....
It is also likely that strawbale houses, much like adobe houses, need to =
=3D
breathe.
strong fired tile which deflects heat and protects the wall and is yet s=
=3D
omewhat=3D20
permeable to moisture movement from inside to outside may be the ideal =
=3D
material in=3D20
this case.
ANSI categorizes tiles as follows:
nonvitreous: more than 7%
semi-vitreous- 3-7 %
vitreous .5-3%
impervious, less than .5 %
wall tile for general purpose interior walls can actually have up to 20%=
=3D
absorption.
wall tile is ungraded.
ANSI (American National Standards Institute) measure permeability to wate=
=3D
r by boiling=3D20
tile in water for 5 hours and dividing its gain in weight by its original=
=3D
dry weight. I think=3D20
over the years a number of folks have posted info on absorption in posts=
=3D
on freeze/thaw.=3D20
often quoting a procedure from Val Cushing's book, and Ron's procedure is=
=3D
similar.
it IS valuable to know the absorption of your claybody at the temperature=
=3D
to which you=3D20
fire. and if glazed, it is always good to have a glaze which fits the bod=
=3D
y and is easy to=3D20
clean.=3D20
All i am trying to say really, is that the range for acceptable absor=
=3D
ption is not as=3D20
narrow as you might think for this application
You might look up stove surrounds in a general tile setting book to find =
=3D
out what to use as=3D20
a substrate (i don't know about straw balle and the thickness of interior=
=3D
plastering, but=3D20
usually cement backerboard along with latex free thinset mortat and grout=
=3D
)
ALso find out whether the backerboard will be set away from the wall. Gen=
=3D
erally, you can=3D20
tile directly to substrate ,(unprotected clearance")if you have 36" inch=
=3D
es of clearance=3D20
between the stove and the wall... if it is closer, down to 12", you need =
=3D
to create an=3D20
airspace between the wall and the subsrate, generally by using hat channe=
=3D
l and allowing=3D20
for circulation of the air between the wall and the tiled panel...
you can easily research this, or , if someone else is doing the installat=
=3D
ion , ask about=3D20
what they will do, as it might affect how you finish the edges of the til=
=3D
ed area.
good success with your project!
Stephani Stephenson
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