search  current discussion  categories  techniques - misc

## freeze thaw resistance

### Mert & Holly Kilpatrick on mon 21 dec 98

Some time ago (11/97) Linda Blossom gave a procedure for checking the
suitability of a clay body for sustaining freezing and thawing. I just
worked through it with my claybody, and I am confused about the formula.
I'm hoping someone out there has the mental energy to follow this train of
thought and tell me what I'm missing.

Here are Linda's original instructions (not verbatim):

Weigh a tile immediately when it comes out of the kiln. That's the dry
weight. Then check the soaked absorption by soaking in water for 24 hours,
drying it and weighing it. That is the wet weight. Subtract the dry
weight from the wet weight and divide the difference by the dry weight.
That's the soaked absorption. Now boil the tile for two hours. Cool the
water and dry and weigh the tile immediately. That's the boiled weight.
Subtract the dry weight from the boiled weight and divide the difference by
the dry weight. That's the boiled absorption. Now divide the soaked
absorption by the boiled absorption. Linda said that this ratio should be
below .78 for the clay to be freeze thaw resistant.

Now, my results: My soaked absorption was .058 (5.8%), and my boiled
absorption was .065 (6.5%). My thought was, "Oh, good, they are very
close, there wasn't a lot of change in the absorption, that must be good."
However, the ratio of .058 to .065 is .89, which is _higher_ than .78, so

To be better, my body should have had a _larger_ discrepancy between soaked
and boiled absorption, according to Linda's instructions. Why would a
bigger swing in absorption under different conditions result in more
freeze-thaw resistance? To me it seemed that the less change, the better.
Can someone explain to me what is going on here?

TIA, Holly
Mert & Holly Kilpatrick
in the Slate Belt, East Bangor, PA

### John Fazzino on tue 22 dec 98

TIA,

Are you just trying to find out if your clay body will survive outdoors in
northern winters? My low tech response is, make some stuff and keep it
outside for a winter and see what happens.

John Fazzino

### Linda Blossom on tue 22 dec 98

Holly,

The theory here is that a very tight body may have a low absorption, but be
lacking in porosity. Porosity is what allows water that made its way into
the pore structure to get out when the water is freezing. The difference
between porosity and absorption may be better understood if you think of a
piece of pottery that has been bisqued. This piece is very absorptive and
underfired. When you put water on it, the water is instantly absorbed.
This is something that happens in the clay, between the particles.
Vitreosity is related to absorbency, not porosity. An underfired clay is
less vitreous and more absorbent because the clay particles are not fused.
Porosity,. however, is what happens as a result of spaces or pores in the
body of the work. It is a structural thing caused usually by grog and other
fillers. If a body is extremely tight, there are no escape routes for
water. A stoneware fired to maturity should not be very absorptive simply
because it is fired to a near vitreous state. However, nothing is
completely fused so water will get in. You need to provide pores to let the
water out. A body needs to be low on the absorption side to be used outside
in areas where it freezes - therefore it should be fired to maturity.
However, it should not be so tight that it has no pore structure. If you
are soaking and weighing a stoneware clay to maturity, and you are following
the formula, you will be determining the pore structure. If your clay has
mostly fine clays and no grog, it probably will be too tight.

I hope this helps. It does work for me - I have never had anything crack in
the winter here in upstate New York. You can get some help for this in the
Val Cushing handbook. The only thing that he didn't do was explain better
the difference between absorption and porosity and define them more
thoroughly. He does explain that a pore structure is necessary and gives
the formula that I posted.

Linda Blossom
Ithaca, NY
blossom@twcny.rr.com

----------------------------Original message----------------------------
Some time ago (11/97) Linda Blossom gave a procedure for checking the
suitability of a clay body for sustaining freezing and thawing. I just
worked through it with my claybody, and I am confused about the formula.
I'm hoping someone out there has the mental energy to follow this train of
thought and tell me what I'm missing.

Here are Linda's original instructions (not verbatim):

Weigh a tile immediately when it comes out of the kiln. That's the dry
weight. Then check the soaked absorption by soaking in water for 24 hours,
drying it and weighing it. That is the wet weight. Subtract the dry
weight from the wet weight and divide the difference by the dry weight.
That's the soaked absorption. Now boil the tile for two hours. Cool the
water and dry and weigh the tile immediately. That's the boiled weight.
Subtract the dry weight from the boiled weight and divide the difference by
the dry weight. That's the boiled absorption. Now divide the soaked
absorption by the boiled absorption. Linda said that this ratio should be
below .78 for the clay to be freeze thaw resistant.

Now, my results: My soaked absorption was .058 (5.8%), and my boiled
absorption was .065 (6.5%). My thought was, "Oh, good, they are very
close, there wasn't a lot of change in the absorption, that must be good."
However, the ratio of .058 to .065 is .89, which is _higher_ than .78, so

To be better, my body should have had a _larger_ discrepancy between soaked
and boiled absorption, according to Linda's instructions. Why would a
bigger swing in absorption under different conditions result in more
freeze-thaw resistance? To me it seemed that the less change, the better.
Can someone explain to me what is going on here?

TIA, Holly
Mert & Holly Kilpatrick
in the Slate Belt, East Bangor, PA

### Cheryl L Litman on wed 23 dec 98

Low tech method:
I tried that method last winter and then the winter turned out to be so
mild that I don't think it's a fair test so I'll leave them out again
this year. But rather than wait 2 years for an answer, a quick test is
my preference!

Cheryl Litman
Somerset, NJ
email: cheryllitman@juno.com

On Tue, 22 Dec 1998 14:10:53 EST John Fazzino writes:
>----------------------------Original
>message----------------------------
>TIA,
>
>Are you just trying to find out if your clay body will survive
>outdoors in
>northern winters? My low tech response is, make some stuff and keep
>it
>outside for a winter and see what happens.
>
>John Fazzino
>

___________________________________________________________________
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]

### Linda Blossom on thu 24 dec 98

Actually a milder winter in which there is a lot of freezing, snowing and
thawing in which things just don't stay frozen are actually harder on the
ceramic and the plants. One winter we stayed under snow from November til
April. It was a year that I lost very few perennials. But in a year when
it seems mild and it snows then it melts then it freezes and then melts -
those are tougher years.

Linda Blossom
2366 Slaterville Rd
Ithaca, NY 14850
607-539-7912
blossom@twcny.rr.com
www.artscape.com
-

----------------------------Original message----------------------------
Low tech method:
I tried that method last winter and then the winter turned out to be so
mild that I don't think it's a fair test so I'll leave them out again
this year. But rather than wait 2 years for an answer, a quick test is
my preference!

Cheryl Litman
Somerset, NJ
email: cheryllitman@juno.com

On Tue, 22 Dec 1998 14:10:53 EST John Fazzino writes:
>----------------------------Original
>message----------------------------
>TIA,
>
>Are you just trying to find out if your clay body will survive
>outdoors in
>northern winters? My low tech response is, make some stuff and keep
>it
>outside for a winter and see what happens.
>
>John Fazzino
>

___________________________________________________________________
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]

### Chris Trabka on fri 25 dec 98

My low tech suggestion:

Soak in water for 2 to 3 days; place in large freezer; repeat several
times.
It shouldn't take more than a month to get several freeze thaw cycles.

Chris
> Low tech method:
> I tried that method last winter and then the winter turned out to be so
> mild that I don't think it's a fair test so I'll leave them out again
> this year. But rather than wait 2 years for an answer, a quick test is
> my preference!
>