On Tue, 18 Jun 2019 13:38:35 +0100, Jeff Layman
wrote:

My understanding is that it is due to old glass having many micro-cracks
and scratches which weaken it and assist in crack propagation throughout
the glass once it starts. Modern glass (and more expensive glass than
the "agricultural" grade glass often used for greenhouses) has a surface
treatment to inhibit the production of these microcracks and scratches
over time. So toughened or tempered glass is much less likely to become
brittle.

Hello,

So to update: the galvanised clips arrived but looked a lot bigger. I
measured the "legs" but both the stainless steel and galvanised ones
are 30mm or 1.25" long. The difference is that the legs are at a 45
degree angle on the stainless ones but at a smaller angle on the
galvanised ones, so the galvanised ones have more depth. The
galvanised ones hold the glass perfectly because the legs are "longer"
and under more tension that the stainless ones.

The glass was stored against my garage wall and it has got wet in the
rain. I've noticed that the glass has a white discolouration in places
that I can't seem to clean off. I'm not sure what this is? Perhaps it
is the micro-cracks you talked about, either refracting light or
perhaps something has got into them?

On 08/07/2019 11:58, Chris Hogg wrote:
On Mon, 08 Jul 2019 10:49:56 +0100, Stephen
wrote:

On Tue, 18 Jun 2019 13:38:35 +0100, Jeff Layman
wrote:

My understanding is that it is due to old glass having many micro-cracks
and scratches which weaken it and assist in crack propagation throughout
the glass once it starts. Modern glass (and more expensive glass than
the "agricultural" grade glass often used for greenhouses) has a surface
treatment to inhibit the production of these microcracks and scratches
over time. So toughened or tempered glass is much less likely to become
brittle.

Hello,

So to update: the galvanised clips arrived but looked a lot bigger. I
measured the "legs" but both the stainless steel and galvanised ones
are 30mm or 1.25" long. The difference is that the legs are at a 45
degree angle on the stainless ones but at a smaller angle on the
galvanised ones, so the galvanised ones have more depth. The
galvanised ones hold the glass perfectly because the legs are "longer"
and under more tension that the stainless ones.

The glass was stored against my garage wall and it has got wet in the
rain. I've noticed that the glass has a white discolouration in places
that I can't seem to clean off. I'm not sure what this is? Perhaps it
is the micro-cracks you talked about, either refracting light or
perhaps something has got into them?

Sheets of glass that are stacked together and get wet can be very
difficult to separate, due to surface tension of the water film
between them holding the panes together. Prize them apart only very
gently or you'll break them, or slide them apart.

The white discolouration is possibly salts that have leached out of
the glass and then redeposited onto the surfaces. You sometimes see a
white deposit on the enclosed surfaces of double-glazing panels that
have failed and moisture has eventually got in, and they've not been
replaced for a long time. Not sure what will shift it - possibly a
very mildly abrasive bath cleaner or similar. It probably doesn't
matter too much anyway for a greenhouse.

To seperatr the sheets a VERY thin bladed knife is the best way. dont
force them or they will break.

On 08/07/2019 12:46, David Hill wrote:
On 08/07/2019 11:58, Chris Hogg wrote:
On Mon, 08 Jul 2019 10:49:56 +0100, Stephen
wrote:

On Tue, 18 Jun 2019 13:38:35 +0100, Jeff Layman
wrote:

My understanding is that it is due to old glass having many
micro-cracks
and scratches which weaken it and assist in crack propagation
throughout
the glass once it starts. Modern glass (and more expensive glass than
the "agricultural" grade glass often used for greenhouses) has a
surface
treatment to inhibit the production of these microcracks and scratches
over time. So toughened or tempered glass is much less likely to become
brittle.

Hello,

So to update: the galvanised clips arrived but looked a lot bigger. I
measured the "legs" but both the stainless steel and galvanised ones
are 30mm or 1.25" long. The difference is that the legs are at a 45
degree angle on the stainless ones but at a smaller angle on the
galvanised ones, so the galvanised ones have more depth. The
galvanised ones hold the glass perfectly because the legs are "longer"
and under more tension that the stainless ones.

The glass was stored against my garage wall and it has got wet in the
rain. I've noticed that the glass has a white discolouration in places
that I can't seem to clean off. I'm not sure what this is? Perhaps it
is the micro-cracks you talked about, either refracting light or
perhaps something has got into them?

Sheets of glass that are stacked together and get wet can be very
difficult to separate, due to surface tension of the water film
between them holding the panes together. Prize them apart only very
gently or you'll break them, or slide them apart.

The white discolouration is possibly salts that have leached out of
the glass and then redeposited onto the surfaces. You sometimes see a
white deposit on the enclosed surfaces of double-glazing panels that
have failed and moisture has eventually got in, and they've not been
replaced for a long time. Not sure what will shift it - possibly a
very mildly abrasive bath cleaner or similar. It probably doesn't
matter too much anyway for a greenhouse.

Surface hydration damage. You can get irridescent surface layers in
glass which has been buried in soil for a while. You may be able to
polish it out but it isn't worth the effort.
To seperatr the sheets a VERY thin bladed knife is the best way. dont
force them or they will break.

I favour sliding them, but a thin blade will help lift them. It is
definitely something to wear stout gloves handling greenhouse glass.

Eye protection isn't a bad idea either - toughened glass can detonate
into copious 3mm glass grit when or if a scratch gets deep enough.

--
Regards,
Martin Brown

On Mon, 15 Jul 2019 13:09:40 +0100, Martin Brown
wrote:

Surface hydration damage. You can get irridescent surface layers in
glass which has been buried in soil for a while. You may be able to
polish it out but it isn't worth the effort.

Is this the same as Chris said: salts that have leached out?

I favour sliding them, but a thin blade will help lift them. It is
definitely something to wear stout gloves handling greenhouse glass.

Eye protection isn't a bad idea either - toughened glass can detonate
into copious 3mm glass grit when or if a scratch gets deep enough.

I have two pieces with a small crack in the glass in the corner; in
both cases there is a line about an inch long. I was wondering whether
to use them or whether to replace them. Is the worry that the crack
could get bigger at any time and the pane shatter?

You may remember I asked whether to glaze the roof or the sides first.
I did the sides first and then stopped because I didn't have enough
panes to do the roof! I have been and bought some more glass today. I
put two panes in the roof on the one side and they were perfectly
square. I went to do the other side only the glass will not sit square
in the frame. The bottom left hand corner of the glass goes in the
bottom left hand corner of the frame but the bottom right hand corner
of the glass is about half an inch above the bottom of the frame!

I'm puzzled by this. A spirit level says the greenhouse is perfectly
level, so it's not as if one corner has sunk. The back of the
greenhouse must be leaning out slightly, causing this section to not
be square. Perhaps the advice to do the roof first is the best advice!
But how do I pull the frame back in square? Why has it only affected
the one side?

Thanks,
Stephen

On 15/07/2019 20:39, Stephen wrote:
On Mon, 15 Jul 2019 13:09:40 +0100, Martin Brown
wrote:

Surface hydration damage. You can get irridescent surface layers in
glass which has been buried in soil for a while. You may be able to
polish it out but it isn't worth the effort.

Is this the same as Chris said: salts that have leached out?

Glass is amorphous so it is a bit ambiguous whether salts have leached
out or the water has hydrated some of the weak spots in the network. The
result is ultimately the same glass that stays wet for extended periods
will get a surface bloom of some sort.

I favour sliding them, but a thin blade will help lift them. It is
definitely something to wear stout gloves handling greenhouse glass.

Eye protection isn't a bad idea either - toughened glass can detonate
into copious 3mm glass grit when or if a scratch gets deep enough.

I have two pieces with a small crack in the glass in the corner; in
both cases there is a line about an inch long. I was wondering whether
to use them or whether to replace them. Is the worry that the crack
could get bigger at any time and the pane shatter?

I wouldn't use any glass that has a visible crack in it. YMMV

You may remember I asked whether to glaze the roof or the sides first.
I did the sides first and then stopped because I didn't have enough
panes to do the roof! I have been and bought some more glass today. I
put two panes in the roof on the one side and they were perfectly
square. I went to do the other side only the glass will not sit square
in the frame. The bottom left hand corner of the glass goes in the
bottom left hand corner of the frame but the bottom right hand corner
of the glass is about half an inch above the bottom of the frame!

I can't quite visualise what you are describing. Are you saying that the
rectangular pieces of glass are too tight a fit at the bottom? You may
need to get a friend to lean gently on the frame to tweak it square.

Once you start (on a calm still day) then you should aim to complete the
job as quickly as possible in one session if you can. The whole thing is
uniquely vulnerable to wind damage when it is partially erected.

It is also the case that a greenhouse with a broken pane facing into the
wind can be very rapidly stripped of glass. I keep a piece of riot
shield with a baton on the back for instant repairs to storm damage. It
didn't protect me from the super storm of Xmas 1998 but that was gusting
to 100mph and crippled the aluminium frame. Glass doesn't bend

I'm puzzled by this. A spirit level says the greenhouse is perfectly
level, so it's not as if one corner has sunk. The back of the
greenhouse must be leaning out slightly, causing this section to not
be square. Perhaps the advice to do the roof first is the best advice!
But how do I pull the frame back in square? Why has it only affected
the one side?

Best bet is measure up to find where the discrepancy lies and use some
assistance to square it up while you get the first few pieces in to the
awkward bit. I suspect once it has some more glass in it will be OK.

--
Regards,
Martin Brown

On Mon, 15 Jul 2019 20:39:07 +0100, Stephen
wrote:



I have two pieces with a small crack in the glass in the corner; in
both cases there is a line about an inch long. I was wondering whether
to use them or whether to replace them. Is the worry that the crack
could get bigger at any time and the pane shatter?

Had a friend with the same problem, seems a waste to ditch an almost
complete pane, he mangaged to source a roll of tape, had a pink
colouring, but srtill perfectly transparent, three years on and the
fix is still working, hopefully someone more knowlegable can tell you
the name of the product, but it was speciffally sold as a glass
repair.

On Tue, 16 Jul 2019 12:13:10 +0100, Martin Brown
wrote:

I can't quite visualise what you are describing. Are you saying that the
rectangular pieces of glass are too tight a fit at the bottom? You may
need to get a friend to lean gently on the frame to tweak it square.

Once you start (on a calm still day) then you should aim to complete the
job as quickly as possible in one session if you can. The whole thing is
uniquely vulnerable to wind damage when it is partially erected.

Sorry for the delay - I was on holiday. It's raining heavily at the
moment, I'll take some photos to explain it more when the weather is
drier.