McCoy, Jack on tue 26 nov 96
I'm planning to make a few ceramic items for outdoor use. But I'm
a bit confused as to what sort of clay I should use.
I've heard that a soft, open clay (possibly one mixed with saw dust) is
best for outside use. This clay will absorb water, but because the saw
dust burns
out leaving air pockets it will handle the freeze/thaw cycles.
On the other hand, I've also heard that you need a clay which is
nearly vitrified, so that it will soak up very little water, which in
turn will
make it resistant to freezing problems.
Help!
Thanks,
Jack
Denis Whitfield on wed 27 nov 96
>----------------------------Original message----------------------------
>I'm planning to make a few ceramic items for outdoor use. But I'm
>a bit confused as to what sort of clay I should use.
>
>I've heard that a soft, open clay (possibly one mixed with saw dust) is
>best for outside use. This clay will absorb water, but because the saw
>dust burns
>out leaving air pockets it will handle the freeze/thaw cycles.
>
>On the other hand, I've also heard that you need a clay which is
>nearly vitrified, so that it will soak up very little water, which in
>turn will
>make it resistant to freezing problems.
>
>Help!
>
>Thanks,
>Jack
>
>
Jack,
In Australia we don't have the same freeze/thaw problem that you do but I
would be going for the vitrified body if I were in your position. I can only
think the burning out of the sawdust would simply increase the number of
opportunities for water to enter (and subsequently freeze and expand).
Regards
Denis
****************************************************************************
DR DENIS WHITFIELD
Senior Lecturer
Co Director, Centre for Ceramic Research, Design and Production
Department of Visual and Peforming Arts
University of Western Sydney, Macarthur
PO Box 555
CAMPBELLTOWN NSW 2560
AUSTRALIA
email: d.whitfield@uws.edu.au
phone: 02 97729345
****************************************************************************
Vince Pitelka on wed 27 nov 96
>I've heard that a soft, open clay (possibly one mixed with saw dust) is
>best for outside use. This clay will absorb water, but because the saw
>dust burns
>out leaving air pockets it will handle the freeze/thaw cycles.
>On the other hand, I've also heard that you need a clay which is
>nearly vitrified, so that it will soak up very little water, which in
>turn will make it resistant to freezing problems.
>Jack
Jack -
As I understand it, neither of the above answers is correct. A vitrified
body will still absorb some water if it is outside through the rainy season,
and then that water will be, for all practical purposes, sealed within the
clay. Such a body can break in freezing. A very porous body will absorb so
much water that it may completely dissintegrate when frozen. I believe that
the allowable absorption rate is between four and seven percent. Such a
body would be tight enough to prevent absorption of large amounts of
moisture, and yet loose enough for any water which is absorbed to easily
evaporate. In a post several months ago I asked if anyone out there got a
copy of the Boston Vally Terracotta Company recipe which was passed out last
year at NCECA. This was an outdoor terracotta recipe, and I would still
like to get this recipe if anyone has it. Architectural terracottas are
often fired into low midrange, which makes them much denser than your
average low-fire clay, and yet still porous enough to breath.
- Vince
Vince Pitelka - vpitelka@Dekalb.Net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts, Smithville TN 37166
LINDA BLOSSOM on fri 29 nov 96
In the Val Cushing Handbook there is a page about this. He goes for a
ratio between the absorbed (soaked)percentage and the boiled (after
soaking)percentage. The ratio should be less than I believe 78%. If you
have a fax number, I could fax you the page that tells exactly how to
determine this. Vince's post explains the reasoning behind the ratio.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
blossom@lightlink.com
http://www.artscape.com
607-539-7912
Tony Hansen on sat 30 nov 96
> >I'm planning to make a few ceramic items for outdoor use. But I'm
> >a bit confused as to what sort of clay I should use.
There is a web page on this at:
http://digitalfire.com/magic/articles/outdoor.htm
There is a special test for this, an ordinary porosity test is not good
enough. See the above page for details and the theory why.
=======================================================================
Tony Hansen, IMC - http://digitalfire.com
Check our web site for news on INSIGHT 5 and visit our ceramic library
Bill Amsterlaw on sat 30 nov 96
There is a good discussion of this topic at
http://digitalfire.com/magic/articles/outdoor.htm
Also, see Cushing Handbook, 3rd edition, p. 17. , available for $22 from Val
M. Cushing, 1497 Water Wells Rd., Alfred Station, NY, 14803.
The main ideas:
Any water that gets absorbed by the clay will expand on freezing.
You might think that the only factor that could protect clay from frost damage
would be to keep the water out. However, there is another factor to be
considered called "closed porosity": The clay can resist damage from the
freezing of absorbed water if it contains enough porous areas which are not
penetrated by water. These closed pores can shrink as the ice expands.
You measure ABSORBANCY of a piece of fired clay by comparing its dry weight to
the weight after soaking in water for 24 hours. You can express this as a
percentage of the dry weight.
You measure TOTAL SATURATION of the piece by comparing its dry weight to the
weight after boiling for 5 hours. (The total saturation represents absorbancy
plus closed porosity.) You can express this as a percentage of the dry
weight.
You want the ratio of ABSORBANCY : TOTAL_SAT to be less than 0.78.
Examples:
1. Even if the absorbancy were only 1%, the clay body would be susceptible to
frost damage if its total absorbancy is also 1% (ratio=1).
This is a body that has no closed pores to absorb the pressure of expanding
ice.
2. If the absorbancy were 7%, the clay would resist frost damage if its total
absorbancy is greater than 9% (ratio=.78). This body absorbs a lot of water
but it contains plenty of closed pores into which ice can expand.
- Bill Amsterlaw (wamster@msn.com)
Plattsburgh, NY
Stephen Forslund on tue 3 dec 96
Tony Hansen wrote:
>
> ----------------------------Original message----------------------------
> > >I'm planning to make a few ceramic items for outdoor use. But I'm
> > >a bit confused as to what sort of clay I should use.
>
> There is a web page on this at:
> http://digitalfire.com/magic/articles/outdoor.htm
>
> There is a special test for this, an ordinary porosity test is not good
> enough. See the above page for details and the theory why.
>
> =======================================================================
> Tony Hansen, IMC - http://digitalfire.com
> Check our web site for news on INSIGHT 5 and visit our ceramic library
I checked the referenced web site and found the info interesting. I
have no scientific info but can provide some observations of what has
happened with outdoor ceramics in my experience.
I make bird feeders using both earthenware and stoneware purchased
prepared from Continental Clay in Minneapolis, MN. I have fired the
stoneware clays in both reduction and oxidation from cone 6 to 10.
These feeders have been left outdoors and used HEAVILY by birds and
squirrels in weather from the high 90's to 50 below with rain, snow and
ice storms. I have taken them down, put them in the laundry tub, soaked
and washed them and hung them back out and have seen no evidence of
damage or even wear. Surprisingly, the earthenware even look like new
after a good soak. The oldest bird feeders are about six years old and
are in excellent shape.
Hope this helps...
Steve forslund
Akita-jin \"Lee Love\" on tue 3 dec 96
A friend of mine has made sculpture and some are large outdoor
fountains. Her clay comes from Continental Clay Co and they recommend
that she fire the earthenware to a higher temperature, so that it wasn't
porous. I think she fired to cone 1, not exactly sure.
Lee
====================================================
/(o\ Lee Love In "St. Paul", MN ' Come see some pixs of my AkitaPup:
\o)/ mailto:LeeLove@millcomm.com ' http://www.millcomm.com/~leelove
mailto:AkitaJin@Cryogen.com ' "It gets late early out there."
-Yogi Berra-
vpitelka@dekalb.net on thu 5 dec 96
Linda -
Almost forgot to ask you - I would love to know more about Val Cushing's
info on outdoor ceramics. If you would, please fax me that page at
615/597-6803, and if you would, include info on how/where I can purchase a
copy of his handbook.
Thanks,
- Vince
Bill Amsterlaw on sat 7 dec 96
Vince:
(repeating some of the info I posted several days ago...)
Cushing Handbook, 3rd edition, p. 17. , available for $22 + S/H from :
Val M. Cushing
1497 Water Wells Rd.
Alfred Station, NY, 14803
(cushing@bigvax.alfred.edu)
There is also a good discussion on freezing effects on clay at
http://digitalfire.com/magic/articles/outdoor.htm
Vince Pitelka asked:
>>
I would love to know more about Val Cushing's info on outdoor ceramics. If
you would, please fax me that page at 615/597-6803, and if you would, include
info on how/where I can purchase a copy of his handbook.
<<
- Bill Amsterlaw (wamster@msn.com)
Plattsburgh, NY
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