LINDA BLOSSOM on sat 22 feb 97
Has anyone made terra cotta, handbuilt or thrown, planters that were
intended to be left outside in a northern climate, year round? If you did,
what was your claybody like and is there anything that you encountered that
you could pass on? I am interested in the freezing and possible breakage.
I would assume that it should have sloped sides that allow the frozen earth
to heave up. Thanks.
Linda Blossom
Ithaca, NY
Ric Swenson on sun 23 feb 97
>----------------------------Original message----------------------------
>Has anyone made terra cotta, handbuilt or thrown, planters that were
>intended to be left outside in a northern climate, year round? If you did,
>what was your claybody like and is there anything that you encountered that
>you could pass on? I am interested in the freezing and possible breakage.
>I would assume that it should have sloped sides that allow the frozen earth
>to heave up. Thanks.
>
>Linda Blossom
>Ithaca, NY
___________reply___________
Erosion happens.
If the body you use is porous and allows water to soak in...and the
temperature goes below freezing...the water will expand (11% I believe...)
and the body will start to deteriorate. For any hope of short term
survival.... Seal the body with a glaze that keeps out the water.....or a
silicon sealant...."Thompsons Water Seal will last a year or two.....or
fire it high enough that the body is tight and you will slow the process..I
doubt it will stop...but you might slow it down.
Age old problem. Only stoneware and porcelain...by definition "NON POROUS"
when fired properly....will last outdoors for any length of time.
Erosion has been around a long time...and thank goodness...it is why we
have clay instead of Igneous rock to make pots from.
Keep potting!
Ric Swenson, Bennington, Vt
Craig Martell on mon 24 feb 97
At 08:38 AM 2/22/97 EST, you wrote:
>----------------------------Original message----------------------------
>Has anyone made terra cotta, handbuilt or thrown, planters that were
>intended to be left outside in a northern climate, year round? If you did,
>what was your claybody like and is there anything that you encountered that
>you could pass on? I am interested in the freezing and possible breakage.
>I would assume that it should have sloped sides that allow the frozen earth
>to heave up. Thanks.
>
>Linda Blossom
>Ithaca, NY
Hi Linda: This isn't a real answer to the question, but a few years ago, I
took a workshop from Svend Bayer and he tells people to line his large
planters with bubble wrap prior to filling with soil and planting. I guess
the bubble wrap allows for expansion and contraction to take place without
any cracking.
Just a thought, Craig Martell-Oregon
David Feild on tue 25 feb 97
Linda--I made terra cotta planters for several years (sizes up to 18" in top
diameter) and used loads of grog in the base clay formula. This doesn't
really solve the problem because the planter then actually takes in more
water which tends to expand and contract during freezing and thawing, but,
somewhat counter intuitively, it did seem to help a great deal. I have
planters outside now that have gone through 20 years of winters, full of
dirt, full of dead plants roots and all. I'll replant them in them this
spring. However, yes, many also didn't make it. But grog, grog, grog and
perhaps a slightly higher firing temperature sure did help. I'll be
interested to see what others say. Good luck. David F
Vince Pitelka on wed 26 feb 97
Linda -
Regarding your request for information on terracotta claybodies which can
stand up to long-term exterior use, perhaps you yourself can help us all out
here, being in the right part of the country. Last fall Robert Wood, from
University of Buffalo, was down here setting up an exhibition of his
wonderful ceramic sculpture. We got to talking about outdoor claybodies,
and he confirmed what has been discussed on Clayart in the past - that a
vitrified claybody is just as bad as one which is too porous. All vitrified
claybodies have some porosity, and over time they absorb a small amount of
water, and when it freezes there is no way for this water to escape. As I
understand it, there is good information on proper absorption levels for
outdoor claybodies in Val Cushing's handbook. But back to my original
intent. Robert Wood told me that at NCECA Rochester last year someone from
Boston Valley Terracotta in Buffalo, NY gave out the recipe for their tried
and true outdoor terracotta. Last fall I posted a request to the list
trying to get this formula, but no response. Maybe you would like to call
Boston Vally Terracotta and see if they will give you the formula. If so,
could you post it to the list?? Hope this works out.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
Evan Dresel on wed 26 feb 97
I have been making a few coiled terra cotta planters etc. and
am also interested in how they hold up. I pumped several potters
for info at a fair last summer and they suggested firing to
at least cone 03 or 02. One also uses terra cotta with added sand
(from Seattle Pottery Supply). He claimed that the sand adds
strength without adding the porosity that grog does. I have fired
my pieces to cone 04 and I noticed a little spalling and cracking
in a birdbath I left full of water through multiple freeze-thaw
cycles. I think the other pot I left out which had drainage did ok.
Then again I don't expect a planter to last forever.
-- Evan
Judith Enright on wed 26 feb 97
I've also made coiled terra cotta planters and the two I chose to keep
in the garden contain jade plants. These pots have lasted perfectly
for the past three years -- I've been very happy with them and,
judging by their proliferation, the jades are happy too.
The terra cotta I use can be fired between ^06 and ^6. The rich
red-brown color is achieved at ^6, and that's what I fired these
particular pots to. I treated the outsides with water sealant and
they have survived several below-freezing episodes over the years
without a problem.
Happy potting --!
-- Judith Enright @ Black Leopard Clayware & Pottery
LINDA BLOSSOM on fri 28 feb 97
Hello Vince and anyone else following this thread,
Well, I did it. I called Boston Valley Terracotta and asked if they would
share the formula for their terracotta. Looking back - what did I really
expect?!! However, I did get some information that will shed some light
here. First, they do use a low fire,06, body that is colored with redart.
It is intentionally porous. Vitrified is NOT the way to go. In fact, the
person I talked to believes that only low fire should be used. They are
the largest maker of terracotta in the country...? That's what I was told.
The method for testing a clay body, given in the Val Cushing handbook is:
Weigh the dry tile. Be sure there is no atmospheric water. Soak the tile
in water for 24 hours and then reweigh it. Subtract the dry from the wet
and this C. Next put the wet tile in boiling water for two hours and then
reweigh it. Subtract the dry weight from the boiled weight and this is B.
Divide C by B. This ratio should be .78 or less. I found that if you take
the tile from the boiling water and try to weigh it, the water in it will
evaporate so fast that if you are using a digital scale, you can watch it
go down. I started adding cooler water until I could handle the tile. Then
I dried it quickly and put it on the already turned on scale. (I carried
the hot water and tile in the pan from the house to the studio so that I
wasn't carrying the tile out of the water). My body which has 50% fireclay
(Hawthorn and Newman) and 20% fine grog had no increase in weight from wet
to boiled. I am first going to try making a batch without the feldspar
that I add. I may try adding some medium grog as well. My absorption was
3.8%.
Any thoughts on what the boiling is supposed to do to the fired clay?
Also, Vince, it seems that Robert Wood (they call him Bob at Boston Valley)
is a friend and the person I spoke with suggested we go to him with any
questions. Do you know him well enough to call him? I wonder why he isn't
online?? So I bounce the ball back to you Vince. I can't believe I asked
a large manufacturer for their formula!
Linda
Ithaca, NY
Margaret Arial on fri 28 feb 97
/There is a sealant used by commercil tile setters that is used to dip then
seal the (very pourous-i.e. Mexican) tile so it won't absorb all the water
from the grout.It is sold in tile stores at a pricy $38 per quart here.I will
notice its name next time i go to the megga hardware or tile store.I read
that sometimes two dippings may be necessary, whether this would fare in
freezing weather i don't know myself.I have had plenty of my pots crack from
freezing that were stoneware even in sunny South Carolina.
Margaret, looking foreward to NCECA but regretting not having enough time to
take all the fun sounding workshops happening nearby because my house and
studio are still beinrenovated.
Vince Pitelka on sat 1 mar 97
At 07:06 AM 2/28/97 -0500, you wrote:
>----------------------------Original message----------------------------
>Hello Vince and anyone else following this thread,
>
>Well, I did it. I called Boston Valley Terracotta and asked if they would
>share the formula for their terracotta. Looking back - what did I really
>expect?!! However, I did get some information that will shed some light
>here. First, they do use a low fire,06, body that is colored with redart.
>It is intentionally porous. Vitrified is NOT the way to go. In fact, the
>person I talked to believes that only low fire should be used. They are
>the largest maker of terracotta in the country...? That's what I was told.
I can't believe I asked
>a large manufacturer for their formula!
>Linda
Linda -
I am surprised that Boston Valley Terracotta was not more forthcoming, since
representatives of their company were giving out the formula last year at
NCECA. Did you mention that to them on the phone? Sounds like you got some
good info from them anyway. I will call Bob Wood. He did an exhibition at
the Craft Center last fall, and if memory serves me, he said he had the
formula at home somewhere. I'll look into it. If I find anything good I'll
post it to the list, since I know many of you have been seeking a good
outdoor formula.
And I truly believe that one should never hesitate to call a large
manufacturer and ask for such information. One never knows how forthcoming
they will be, and after all, what do we have to loose?
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
Tony Hansen on sat 1 mar 97
> Vitrified is NOT the way to go.
Exactly. Iron bodies turn brown when they vitrify, the red color depends on
stopping well short of vitrification. Most terra cotta bodies begin to brown out
suddenly above cone 1 and many lower. Even if the body fires red, if it is burne
too hot transparent glazes will flux the surface enough to turn it brown.
Low fire red bodies can be very strong, I have measured a cone 1 red burning bod
strength at 10,000 lbs/square inch, that's as strong as many cone 10 porcelains?
You can cast with 100% red art and get a nice product. However it may be too red
and doesn't handle that well. Try 25% of a large particle size kaolin, 25%
feldspar, and 50% redart. If this is deflocculated properly it casts like a drea
It is very important to understand the deflocculation process to use slip proper
check the web page at http://www.ceramicsoftware.com/education/articles/slip.htm
Don't be to worried about high porosity. Many commercial wares are 6-8% and yet
are very strong. Just make sure the glaze fits (can survive a hot water:ice wate
test) and strengthens the ware. Check the web page at
http://www.ceramicsoftware.com/education/articles/control.htm
At the bottom it has links to test procedure pages that go into great detail how
carry out standard testing.
--
=================================================================
Tony Hansen, IMC - Get INSIGHT 5 beta or The Magic of Fire II at
http://digitalfire.com or http://www.ceramicsoftware.com
koratpot@korat.loxinfo.co.th on thu 6 mar 97
> ----------------------------Original message----------------------------
> > Vitrified is NOT the way to go.
> Check the web page at
> http://www.ceramicsoftware.com/education/articles/control.htm
> At the bottom it has links to test procedure pages that go into great detail h
> carry out standard testing.
..........................................................
I have followed this device and done the test, and found that my clay
absorbs no more water after being boiled for five hours than it did
after being soaked for 24 hours. So it won't work as outdoor planters
in cold places.
Next question: how would I modify this body to make it work? How do
you build "closed porosity" into a clay body? Is it a function of
particle size, or what?
I also would like to know how a vitrified body can possiblly absorb
water. Seems to me that if absorbtion is zero, that clay should go
safely through freeze-thaw cycles. How could water do it any harm?
What am I missing here?
Nikom
koratpot@korat.loxinfo.co.th
Tony Hansen on fri 7 mar 97
> Next question: How do you build "closed porosity" into a clay body?
> Is it a function of particle size, or what?
I trust you weighed accurately. I will pass this question on to the
technician in our brick division, he will know. However I think it is
important to have a good distribution of particle sizes and some coarser
particles to encourage development of channels.
> I also would like to know how a vitrified body can possiblly absorb
> water. Seems to me that if absorbtion is zero, that clay should go
> safely through freeze-thaw cycles. How could water do it any harm?
'Vitrification' is a process and a very subjective term. A vitrified
bone china is almost melted, a vitrified porcelain will be zero porosity
but nowhere near melting, a vitrified white stoneware may have 1-2%
porosity, a vitrified pipe might have 4-5% porosity, etc. Very few potters
use zero-porosity bodies because they cannot put up with the associated
warping in the kiln. Lots of potters use bodies they believe are
zero-porosity but this is not the case. I've seen people who fire pottery
with 10% porosity who believe that their ware was zero porosity.
There are tradeoffs between vitrification, fired strength, stability in
the kiln, fuel costs, etc. Many clays simply cannot be fired to zero
porosity before they blister and become brittle.
--
=================================================================
Tony Hansen, IMC - Get INSIGHT 5 beta or The Magic of Fire II at
http://digitalfire.com or http://www.ceramicsoftware.com
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