Or more likely not. In previous years I've had the odd FPP crack, with
it most likely being the top of the rim which cracks off. This year I've
already seen four "FPP" with damaged rims, one of them having several
cracks in the main body. The latter could be due to expansion of the
damp soil, but the rims are frost damage from damp getting into the
terracotta. Minimum temps here were around -6 to -7°C.

I've a feeling that glazed pots fare better, but am going back to
plastic. How have others here been getting on?

--

Jeff

On 16/03/2023 14:16, Jeff Layman wrote:
> Or more likely not. In previous years I've had the odd FPP crack, with
> it most likely being the top of the rim which cracks off. This year I've
> already seen four "FPP" with damaged rims, one of them having several
> cracks in the main body. The latter could be due to expansion of the
> damp soil, but the rims are frost damage from damp getting into the
> terracotta. Minimum temps here were around -6 to -7°C.
>
> I've a feeling that glazed pots fare better, but am going back to
> plastic. How have others here been getting on?
>

Perhaps you could coat unglazed ones with silicone treatment.
From some specialised knowledge relating to rare architectural heritage
vertical tiles called mathematical tiles.
These are usually unglazed terracotta (exceptionally "Brighton" black
ones are glazed) and if treated with silicone, not only does it stop
driving rain prenetrating through, it stops frost damage making them
fall off the wall. Unsure how often they need spray retreating though
and whether toxic to plants , as lichen/moss seems reluctant to grow on
such treated tiles

--
Global sea level rise to 2100 from curve-fitted existing altimetry data
<http://diverse.4mg.com/slr.htm>

On 16/03/2023 15:34, N_Cook wrote:
> On 16/03/2023 14:16, Jeff Layman wrote:
>> Or more likely not. In previous years I've had the odd FPP crack, with
>> it most likely being the top of the rim which cracks off. This year I've
>> already seen four "FPP" with damaged rims, one of them having several
>> cracks in the main body. The latter could be due to expansion of the
>> damp soil, but the rims are frost damage from damp getting into the
>> terracotta. Minimum temps here were around -6 to -7°C.
>>
>> I've a feeling that glazed pots fare better, but am going back to
>> plastic. How have others here been getting on?
>>
>
> Perhaps you could coat unglazed ones with silicone treatment.
> From some specialised knowledge relating to rare architectural heritage
> vertical tiles called mathematical tiles.
> These are usually unglazed terracotta (exceptionally "Brighton" black
> ones are glazed) and if treated with silicone, not only does it stop
> driving rain prenetrating through, it stops frost damage making them
> fall off the wall. Unsure how often they need spray retreating though
> and whether toxic to plants , as lichen/moss seems reluctant to grow on
> such treated tiles
>

The other consideration ,it could be, in a sense, damage rather than
frost damage. Do the frosted pots get direct sunlight the next morning ,
as its this abrupt positive temp change that seems to be the killer
of the tiles. ie screen the pots from sunlight when frost is around

--
Global sea level rise to 2100 from curve-fitted existing altimetry data
<http://diverse.4mg.com/slr.htm>

On 16/03/2023 15:38, N_Cook wrote:
> in a sense, damage rather than frost damage

crap text editor/windoze, slower than my slow typing

in a sense, sun damage rather than frost damage

--
Global sea level rise to 2100 from curve-fitted existing altimetry data
<http://diverse.4mg.com/slr.htm>

On 16/03/2023 14:16, Jeff Layman wrote:
> Or more likely not. In previous years I've had the odd FPP crack, with
> it most likely being the top of the rim which cracks off. This year I've
> already seen four "FPP" with damaged rims, one of them having several
> cracks in the main body. The latter could be due to expansion of the
> damp soil, but the rims are frost damage from damp getting into the
> terracotta. Minimum temps here were around -6 to -7°C.
>
> I've a feeling that glazed pots fare better, but am going back to
> plastic. How have others here been getting on?
>
All our glazed pots are OK as far as I can tell and they are out in the
garden on the low wall, so exposed. Noticed yesterday one of our
terracotta pots behind our greenhouse has lost it's rim.
--
Regards
Bob Hobden

On 16/03/2023 15:42, N_Cook wrote:
> On 16/03/2023 15:38, N_Cook wrote:
>> in a sense, damage rather than frost damage
>
> crap text editor/windoze, slower than my slow typing
>
> in a sense, sun damage rather than frost damage
>
>
>
No, its a well known myth., the freezing happens at night in the cold,
the sun warms the pots, the ice melts and the shattered bits fall off.

The only place you get direct sun damage is hot dry deserts. Onion or
exfoliation weathering

--
When plunder becomes a way of life for a group of men in a society, over
the course of time they create for themselves a legal system that
authorizes it and a moral code that glorifies it.

Frédéric Bastiat

On 16/03/2023 15:42, N_Cook wrote:
> On 16/03/2023 15:38, N_Cook wrote:
>> in a sense, damage rather than frost damage
>
> crap text editor/windoze, slower than my slow typing
>
> in a sense, sun damage rather than frost damage

No, it's as TNP answered. Three of the four pots are sheltered by a
north-facing wall. They only get morning sun well after the spring equinox.

I can't remember for certain, but I think these were Apta "frost-proof"
pots (I never buy the weasel-worded "frost-resistant" pots). They were
plain terracotta, so I was a bit surprised that they were described as
frost-proof. Several years ago I had to replace several Yorkshire
Potteries "frost-proof" bowls.

--

Jeff

On 16/03/2023 19:11, Jeff Layman wrote:
> On 16/03/2023 15:42, N_Cook wrote:
>> On 16/03/2023 15:38, N_Cook wrote:
>>> in a sense, damage rather than frost damage
>>
>> crap text editor/windoze, slower than my slow typing
>>
>> in a sense, sun damage rather than frost damage
>
> No, it's as TNP answered. Three of the four pots are sheltered by a
> north-facing wall. They only get morning sun well after the spring equinox.
>
> I can't remember for certain, but I think these were Apta "frost-proof"
> pots (I never buy the weasel-worded "frost-resistant" pots). They were
> plain terracotta, so I was a bit surprised that they were described as
> frost-proof. Several years ago I had to replace several Yorkshire
> Potteries "frost-proof" bowls.
>

Interesting observation going the other way back to my interest. From
this thread the breaks at the rim of clay planters, is where there is a
large change of thickness of material.
Mathematical tiles have this rain and frost failure potential but plain
hanging tiles don't. Plain tiles are constant thickness but the
mathematical ones , to mimic laid up bricks, have an abrupt change of
thickness also.

--
Global sea level rise to 2100 from curve-fitted existing altimetry data
<http://diverse.4mg.com/slr.htm>

On Thu, 16 Mar 2023 14:16:31 +0000, Jeff Layman <Jeff@invalid.invalid>
wrote:

>Or more likely not. In previous years I've had the odd FPP crack, with
>it most likely being the top of the rim which cracks off. This year I've
>already seen four "FPP" with damaged rims, one of them having several
>cracks in the main body. The latter could be due to expansion of the
>damp soil, but the rims are frost damage from damp getting into the
>terracotta. Minimum temps here were around -6 to -7°C.
>
>I've a feeling that glazed pots fare better, but am going back to
>plastic. How have others here been getting on?

The cause, as others have said, is moisture getting into the pores of
the earthenware pot, freezing and expanding, and thus cracking the
pot. The higher the firing temperature of the pot during manufacture,
the more resistant to frost damage it is, because (a) the high-fired
pots have fewer pores and (b) because of (a) they are inherently
stronger.

Higher firing temperatures require more fuel, so expect to see fewer
genuine frost-proof pots in the future as fuel costs rise.

But that's no help to you!

Glazed pots are much less likely to absorb water, because the glaze
seals the surface, although if the underside of the base or the inside
are not glazed, moisture can still penetrate.

As a first off, simply painting the pots all over, inside and out,
with a good exterior paint should make a difference, if you can get an
exterior colour that you like for pots.

NC's suggestion of silicone seems a good idea, too.

--
Chris

Gardening in West Cornwall, very mild, sheltered
from the West, but open to the North and East.

On 16/03/2023 14:16, Jeff Layman wrote:
> Or more likely not. In previous years I've had the odd FPP crack, with
> it most likely being the top of the rim which cracks off. This year I've
> already seen four "FPP" with damaged rims, one of them having several
> cracks in the main body. The latter could be due to expansion of the
> damp soil, but the rims are frost damage from damp getting into the
> terracotta. Minimum temps here were around -6 to -7°C.
>
> I've a feeling that glazed pots fare better, but am going back to
> plastic. How have others here been getting on?

My experience is that porous pots crack. I generally use faux terracotta
plastic pots. If you want to go to the trouble of making your own
concrete pots, include some waterproofing additive in the mix.

--
Rusty Hinge
To err is human. To really foul things up requires a computer and the BOFH.

On 17/03/2023 07:33, Chris Hogg wrote:
> On Thu, 16 Mar 2023 14:16:31 +0000, Jeff Layman <Jeff@invalid.invalid>
> wrote:
>
>> Or more likely not. In previous years I've had the odd FPP crack, with
>> it most likely being the top of the rim which cracks off. This year I've
>> already seen four "FPP" with damaged rims, one of them having several
>> cracks in the main body. The latter could be due to expansion of the
>> damp soil, but the rims are frost damage from damp getting into the
>> terracotta. Minimum temps here were around -6 to -7°C.
>>
>> I've a feeling that glazed pots fare better, but am going back to
>> plastic. How have others here been getting on?
>
>
> The cause, as others have said, is moisture getting into the pores of
> the earthenware pot, freezing and expanding, and thus cracking the
> pot. The higher the firing temperature of the pot during manufacture,
> the more resistant to frost damage it is, because (a) the high-fired
> pots have fewer pores and (b) because of (a) they are inherently
> stronger.
>
> Higher firing temperatures require more fuel, so expect to see fewer
> genuine frost-proof pots in the future as fuel costs rise.
>
> But that's no help to you!
>
> Glazed pots are much less likely to absorb water, because the glaze
> seals the surface, although if the underside of the base or the inside
> are not glazed, moisture can still penetrate.
>
> As a first off, simply painting the pots all over, inside and out,
> with a good exterior paint should make a difference, if you can get an
> exterior colour that you like for pots.
>
> NC's suggestion of silicone seems a good idea, too.
>

Certainly the case with bricks, cheaper, lower firing temperature ones
are more liable to spalling with the same rain/frost cycling .
The weather facing section, a few mm thick, shears away leaving an
unsightly rough surface

--
Global sea level rise to 2100 from curve-fitted existing altimetry data
<http://diverse.4mg.com/slr.htm>

On 17/03/2023 09:25, N_Cook wrote:
> On 17/03/2023 07:33, Chris Hogg wrote:
>> On Thu, 16 Mar 2023 14:16:31 +0000, Jeff Layman <Jeff@invalid.invalid>
>> wrote:
>>
>>> Or more likely not. In previous years I've had the odd FPP crack, with
>>> it most likely being the top of the rim which cracks off. This year I've
>>> already seen four "FPP" with damaged rims, one of them having several
>>> cracks in the main body. The latter could be due to expansion of the
>>> damp soil, but the rims are frost damage from damp getting into the
>>> terracotta. Minimum temps here were around -6 to -7°C.
>>>
>>> I've a feeling that glazed pots fare better, but am going back to
>>> plastic. How have others here been getting on?
>>
>>
>> The cause, as others have said, is moisture getting into the pores of
>> the earthenware pot, freezing and expanding, and thus cracking the
>> pot. The higher the firing temperature of the pot during manufacture,
>> the more resistant to frost damage it is, because (a) the high-fired
>> pots have fewer pores and (b) because of (a) they are inherently
>> stronger.
>>
>> Higher firing temperatures require more fuel, so expect to see fewer
>> genuine frost-proof pots in the future as fuel costs rise.
>>
>> But that's no help to you!
>>
>> Glazed pots are much less likely to absorb water, because the glaze
>> seals the surface, although if the underside of the base or the inside
>> are not glazed, moisture can still penetrate.
>>
>> As a first off, simply painting the pots all over, inside and out,
>> with a good exterior paint should make a difference, if you can get an
>> exterior colour that you like for pots.
>>
>> NC's suggestion of silicone seems a good idea, too.
>>
>
> Certainly the case with bricks, cheaper, lower firing temperature ones
> are more liable to spalling with the same rain/frost cycling .
> The weather facing section, a few mm thick, shears away leaving an
> unsightly rough surface

I've got the national collection of spalled bricks here!

--

Jeff

On 16/03/2023 19:33, N_Cook wrote:
> On 16/03/2023 19:11, Jeff Layman wrote:
>> On 16/03/2023 15:42, N_Cook wrote:
>>> On 16/03/2023 15:38, N_Cook wrote:
>>>> in a sense, damage rather than frost damage
>>>
>>> crap text editor/windoze, slower than my slow typing
>>>
>>> in a sense, sun damage rather than frost damage
>>
>> No, it's as TNP answered. Three of the four pots are sheltered by a
>> north-facing wall. They only get morning sun well after the spring
>> equinox.
>>
>> I can't remember for certain, but I think these were Apta "frost-proof"
>> pots (I never buy the weasel-worded "frost-resistant" pots). They were
>> plain terracotta, so I was a bit surprised that they were described as
>> frost-proof. Several years ago I had to replace several Yorkshire
>> Potteries "frost-proof" bowls.
>>
>
> Interesting observation going the other way back to my interest. From
> this thread the breaks at the rim of clay planters, is where there is a
> large change of thickness of material.
> Mathematical tiles have this rain and frost failure potential but plain
> hanging tiles don't. Plain tiles are constant thickness but the
> mathematical ones , to mimic laid up bricks, have an abrupt change of
> thickness also.
>
What happens is the rims are soaked through with water, being porous and
on top, They are also the most exposed part and they are not in contact
with any soil, which would keep them stabilised temperature wise, so
they get the coldest.

Thickness probably has a slight effect in that the outside will freeze
and expand whilst the inside might not. But its the position that is I
think most relevant.

Freeze cracking leads to spalling - flaking off in layers., Differential
temperature cracking will usually lead to large cracks across an
otherwise intact structure.

I've had both, but spallation (sp?) dominates on the large terracotta
pots my ex was fond of purchasing,. I am now down to the ones that have
survived. Darwinian action in clay...

--
If you tell a lie big enough and keep repeating it, people will
eventually come to believe it. The lie can be maintained only for such
time as the State can shield the people from the political, economic
and/or military consequences of the lie. It thus becomes vitally
important for the State to use all of its powers to repress dissent, for
the truth is the mortal enemy of the lie, and thus by extension, the
truth is the greatest enemy of the State.

Joseph Goebbels

On 17/03/2023 08:02, RustyHinge wrote:
> On 16/03/2023 14:16, Jeff Layman wrote:
>> Or more likely not. In previous years I've had the odd FPP crack, with
>> it most likely being the top of the rim which cracks off. This year
>> I've already seen four "FPP" with damaged rims, one of them having
>> several cracks in the main body. The latter could be due to expansion
>> of the damp soil, but the rims are frost damage from damp getting into
>> the terracotta. Minimum temps here were around -6 to -7°C.
>>
>> I've a feeling that glazed pots fare better, but am going back to
>> plastic. How have others here been getting on?
>
> My experience is that porous pots crack. I generally use faux terracotta
> plastic pots. If you want to go to the trouble of making your own
> concrete pots, include some waterproofing additive in the mix.
>
Its the same as spallation in brickwork. Hard engineering style bricks
dont absorb water.

Cheap shit will.

Someone else mentioned firing temperature. It sounds eminently plausible.

With brick, the answer is to pay more for a harder brick, or use a water
repellent coating that soaks on and stop water absorption.

Probably work fine on a pot but will change its appearance slightly.

--
The New Left are the people they warned you about.

On 17/03/2023 09:25, N_Cook wrote:
> On 17/03/2023 07:33, Chris Hogg wrote:
>> On Thu, 16 Mar 2023 14:16:31 +0000, Jeff Layman <Jeff@invalid.invalid>
>> wrote:
>>
>>> Or more likely not. In previous years I've had the odd FPP crack, with
>>> it most likely being the top of the rim which cracks off. This year I've
>>> already seen four "FPP" with damaged rims, one of them having several
>>> cracks in the main body. The latter could be due to expansion of the
>>> damp soil, but the rims are frost damage from damp getting into the
>>> terracotta. Minimum temps here were around -6 to -7°C.
>>>
>>> I've a feeling that glazed pots fare better, but am going back to
>>> plastic. How have others here been getting on?
>>
>>
>> The cause, as others have said, is moisture getting into the pores of
>> the earthenware pot, freezing and expanding, and thus cracking the
>> pot. The higher the firing temperature of the pot during manufacture,
>> the more resistant to frost damage it is, because (a) the high-fired
>> pots have fewer pores and (b) because of (a) they are inherently
>> stronger.
>>
>> Higher firing temperatures require more fuel, so expect to see fewer
>> genuine frost-proof pots in the future as fuel costs rise.
>>
>> But that's no help to you!
>>
>> Glazed pots are much less likely to absorb water, because the glaze
>> seals the surface, although if the underside of the base or the inside
>> are not glazed, moisture can still penetrate.
>>
>> As a first off, simply painting the pots all over, inside and out,
>> with a good exterior paint should make a difference, if you can get an
>> exterior colour that you like for pots.
>>
>> NC's suggestion of silicone seems a good idea, too.
>>
>
> Certainly the case with bricks, cheaper, lower firing temperature  ones
> are more liable to spalling with the same rain/frost cycling .
> The weather facing section, a few mm thick, shears away leaving an
> unsightly rough surface
>
+1. Absolutely my experience too And at the top of walls mostly. where
rain hits hardest and its coldest at night

--
“It is dangerous to be right in matters on which the established
authorities are wrong.”

― Voltaire, The Age of Louis XIV

On 16/03/2023 14:16, Jeff Layman wrote:
> Or more likely not. In previous years I've had the odd FPP crack, with
> it most likely being the top of the rim which cracks off. This year I've
> already seen four "FPP" with damaged rims, one of them having several
> cracks in the main body. The latter could be due to expansion of the
> damp soil, but the rims are frost damage from damp getting into the
> terracotta. Minimum temps here were around -6 to -7°C.
>
> I've a feeling that glazed pots fare better, but am going back to
> plastic. How have others here been getting on?
>

Perhaps ignore any labels saying frost proof and go by the colour
indicating firing temperature. ISTR it is whitish pink, pink,
pinkish-orange,orange,dark orange, and brown for highest ,its starting
colour curiously, if terra cotta but probably mixed with other clays
for cost reasons

--
Global sea level rise to 2100 from curve-fitted existing altimetry data
<http://diverse.4mg.com/slr.htm>