Polycarbonate glazing and winter growers

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conolady
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Polycarbonate glazing and winter growers

Post by conolady »

Does anyone out there have a 6mm polycarbonate greenhouse who grows AND FLOWERS winter growing mesembs? I'm considering the glazing for a new house and wondering whether the 11% light transference difference between it and toughened glass would impede the flowering of my babies. I could just use polycarb on the roof, of course...
First it was orchids, then, since c.2001, cacti and succulents. I'm into South African plants, mainly conos, lithops and haworthias, with a few cacti, especially 'posh' mamms, turbs and other smalls. Now it’s stapeliads as well...
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el48tel
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Re: Polycarbonate glazing and winter growers

Post by el48tel »

For what it's worth ....
My greenhouse supplier says polycarbonate is lighter and so a greenhouse not anchored to the ground is likely to fly in a high wind. It discolours. It loses its plastic nature and becomes brittle. It is a better insulator than glass. It is safer to use should you have young children in the area.
Endeavouring to grow Aylostera, Echinocereus, Echinopsis, Gymnocalycium, Matucana, Rebutia, and Sulcorebutia. Fallen out of love with Lithops and aggravated by Aeoniums.
Currently being wooed by Haworthia, attempting hybridisation, and enticed by Mesembs.
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habanerocat
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Re: Polycarbonate glazing and winter growers

Post by habanerocat »

From my research earlier in the year I was of the opinion that polycarbonate was well up there if not better at transmitting light than general glass. So I wasn't that worried about that factor.

You need to get UV grade polycarbonate otherwise the ordinary grade will yellow quickly. UV grade is only guaranteed for 10 years which may be important to you.

Also polycarbonate expands and contacts in heat more that glass. So you need to allow for that if you have a large span. So if bolting you need to allow for movement. Best sit it on a bed of UV grade silicon.
davidfair
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Re: Polycarbonate glazing and winter growers

Post by davidfair »

I have 5-ply opal-coloured polycarbonate. It is quoted to transmit 67% of light (ie compared to just fresh air between the plants and the sun). Clear polycarbonate is even better. It looks less than 67% to the naked eye because it also diffuses the light and so you don't get sharp shadows, but I think this is a good thing for the plants and the comfort of our eyes. I have never had any yellowing or brittling of the polycarbonate and it's been up for 10 years so far. It is far safer than glass but it makes an almighty din when we get hail or heavy rain. My mesembs and everything else flower perfectly well, and many mesembs in flower at the moment.
David
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KarlR
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Re: Polycarbonate glazing and winter growers

Post by KarlR »

I can't remember where I read it or what the percentages were, but I believe it's the case that glass lets through more light on sunny days whereas polycarbonate lets through more light on overcast days because of the light diffraction in the polycarbonate. I am unsure whether this interesting side effect of polycarbonate amounts to a real meaningful amount of light though.

Wind is no problem for polycarbonate unless you're very exposed to strong winds perhaps.

It is more difficult to clean than glass, particularly if you get water inside the polycarbonate leading to algae growth. This happened to some of my poly sheets because the tape covering all the small «tubes» (?) had started to rot. Admittedly I should have redone the tape years and years ago, so I'm only blaming myself. Still, I do feel that my glasshouse is easier to clean.

I'm personally not going to use polycarbonate for my next greenhouse, but poly does have its merits.
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conolady
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Re: Polycarbonate glazing and winter growers

Post by conolady »

Many thanks for the info, guys. I'll have a think...
First it was orchids, then, since c.2001, cacti and succulents. I'm into South African plants, mainly conos, lithops and haworthias, with a few cacti, especially 'posh' mamms, turbs and other smalls. Now it’s stapeliads as well...
peter831shaw
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Re: Polycarbonate glazing and winter growers

Post by peter831shaw »

Polycarbonate comes in several configurations, corrugated and multi-walled (2 and 3 layers) as well as clear and diffuse.

The more layers the more light gets reflected back of sideways. Corrugated has 20% more surface area than the layered forms, resulting in greater surface area = greater heat loss.

Diffuse creates a shadeless environment due to the light bouncing around,

the transmission rates of light are all over the board, but.... a lighter material requires less structural support (trusses etc) than glass so the overall transmission is greenhouse dependent. From my measuring lots of greenhouses, 50-65% of the outside light is transmitted on a sunny day.

If you are worried about coloration of your plants then avoid polycarbonate as it blocks more UV light which triggers coloration of many plants.

Glass and poly film as well as acrylic covers allow more UV.

I have seen lithops flower under old dirty fiberglass covers.

Peter
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conolady
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Re: Polycarbonate glazing and winter growers

Post by conolady »

That's very interesting, Peter. Thanks.
First it was orchids, then, since c.2001, cacti and succulents. I'm into South African plants, mainly conos, lithops and haworthias, with a few cacti, especially 'posh' mamms, turbs and other smalls. Now it’s stapeliads as well...
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