"Martin Brown" wrote in message
...
In message , Franz Heymann
writes
I am mean that lightweight double-skinned stuff which can be cut
with
a pocket knife. It has an overall thickness of about 5 or 6 mm.
It
is translucent, but not transparent.

Some grades are almost transparent. And if you want it to stay that
way
be sure to assemble it with the UV stabilised side facing outwards.

Which urgler would like to report on its usefulness for making
"rectangular cloches", or small portable frames?

I have one outside. Two sheets clamped on a wooden frame. Actually
it is
made from the 1cm thick grade intended for conservatories from my
old
greenhouse. The 6mm stuff is a bit weak to be self supporting for
large
cloches. The only thing to watch is if the wind gets under it.

Actually I have one frame constructed by using the 1 cm transparent
stuff. It is made proof against being lifted by the wind by having
large corner gussets at ground level, with full pots always standing
on them. It has not blown over in 15 years. Unfortunately there is
now so much algal growth inside the hollows that is losing a lot of
light.

What does one use for gluing two pieces together?

You don't glue it reliably with any strength. But you can bolt it to
a
frame or to itself with suitable plastic washers to spread the load.
Clear silicone rubber sealant can be useful for weather proofing.

Silicone fishtank sealant sticks to glass like the proverbial shit to
a blanket, and makes a very strong structure. I now have a few trial
joints under test, using that stuff and the 6 mm polycarbonate.

I do have one small large cloche made entirely of this material, with
the corners sewn together using nylon string and a series of drilled
holes in the material. It works fine, but making it is an
excruciatingly tedious procedure. The finished object is pegged on to
the soil with stout wire stakes.

The 6mm grade you mention is ideal for small opening roof vents on a
greenhouse since it is indestructible if the wind grabs hold of it
(unlike glass).

I intend to build my next greenhouse entirely out of twinwall
polycarbonate.

I suspect that you will find it to be superior to a glass house.
Double glazing and all that...

Franz

Franz