My HFGH has UV coating on both sides.
I think that is true of all of them but not sure. If you know the name of the manufacture you could contact them.

If it's already been dismantled, the only things I can think of that might give you a clue, would be any residual exterior sealant on the edges or exterior dust on one side.

Or, if viewed at an angle, if there is any hint of discoloration on one side, it might indicate it having been directly exposed to the sun.

Otherwise, I honestly don't know how you can tell just by looking, but hopefully, there is some other means of telling the difference and that someone on this forum will reveal what it is.

Thanks, gw - another plus for HFGH

Unfortunately, for my GH, only one side has the UV coating (according to the manual). The retailer doesn't know how to find the correct side once the covering material which idicated the sunward side has been removed.

I can't find the post but somewhere I remember seeing someone sticking strips of newspaper up the channels.

The side that lets UV through yellows the newspaper.

I did a quick search and found "UV Sensitive Beads" but I think they may be too big to stuff up the channels.

Here is a link that might be useful: An idea....

OK!

Looks like I should have done a better search before I posted.

I didn't realize there were so many items out there that were UV sensitive!

Take a look at this site to give you ideas. You may be able to find a kids toy, nail polish or some other novelty locally that is cheap and you could use.

Personally I would buy that teddy bear.... and RIP his toenails off!!!!!

:)

Here is a link that might be useful: Loads of ideas!

By golly, Chris found the answer!

Domeman: That color changing nail polish might be an easy solution, with no need to try to shove bits of newspaper into the channels. Just coat a small piece of metal or plastic with the polish color combination that has the greatest obvious change from sun to dark, then hold the piece under the polycarb panels in sunlight, to see which side blocks the UV.

Or, as Chris suggests: treat yourself to a Teddy. Come to think on it, Teddy could then become your GH mascot and tell you if any of your UV coating was failing long before you might otherwise notice a problem. Also, if you had to import, nail polish could cost more to ship than it's worth, as it's an ORM, but Teddy would probabaly ship as just a harmless toy.

But will that company ship to Australia? Or, is there a distributor there? Anyway, now you know. There ARE products that will make determining which side of polycarb has the UV coating quick, simple and if you go with Teddy, kind of fun.

OK Some great suggestions but........

Unfortunately the common fluoro toys react to fairly ordinary light (harmless UV). They can be 'charged' by ordinary fluor lights. So sunlight fluoresces these materials right though the polycarb.

I am talking to UV/fluorescence experts and will report back. Not such a simple problem it seems.

Domeman: I'm so sorry. I thought you had a simple solution and could have some fun waving a Teddy around while testing your polycarb. Please let us know if you find the real thing.

I think the idea of putting newspaper under the Poly is still a good one. Just take a few sheets a time and lean them against a row of sawhorses that you've placed newsprint under. Just weight down the paper to keep it from blowing away, and tarp the ends to prevent any other light from entering. Of course you could install the panels on your GH frame, tape newspapers to the inside of the Poly, and then swap the ones the yellow the fastest.

If I am not mistaken, there has to be a device capable of measuring UV. Some of the local TV and radio stations give the UV index during the summer, so you might check with a University or weather center to see what they use, and if you can get one.

The problem is that there are lots of different kinds of UV (from about 350 down to a few nm). A much bigger range than visible light. I think domeman's concern is with UVC or something.

Tanning lotion?

dcarch

Question - does one not want the entire light spectrum in the greenhouse to maximize growth?

What is the purpose of the UV covering in a greenhouse application?

"What is the purpose of the UV covering in a greenhouse application?"
Plastics will not last long unless UV protected.

dcarch

Esobofh- Plants do need most of the visible light spectrum, from 400-700 nm. However, the UV wavelength is not used in photosynthesis, and does indeed damage plastic. So, by inhibiting the UV, the plastic will last longer, and the plants will do just fine.

UV is helpful for insects to locate flowers.

They see UV, and flowers glow under UV.

dcarch

This is a good thread, until domeman comes back to us and tells us how he managed to work out which side of his twin walled polycarbonate had the UV blocking additive on it this discussion on UV blocking with respect to insects is interesting.

If you look at studies then the fact that greenhouse coverings block UV is great for reducing the numbers of insect pests in a greenhouse.

Basically they are blind, they cannot see. Even in daylight, the have difficulty finding food, and can I say this on a gardening forum? Ummm.. they have difficulty in finding a mate and having sex. Good for us with UV free greenhouses! (OK so insects work by scent too, so they can still eat and do the other thing but they are doing it in less than ideal conditions)

HOWEVER! If you need insects in your greenhouse to pollonate crops in there then the UV blocking is a real disadvantage!

Here is a link that might be useful: Insects and UV light

Thanks everyone!

At this stage I have decided that I need to pass just a limited band of UV through the sheet from each side until I see the difference. This means using a UV light and narrow band UV filters. I expect to do these test in the next week. Without a filter the result does not make any distinction using comon UV materials as suggested in some posts, since most of these materials respond to 'near UV colors' and the coatings do not effect these colors.

Must admit that I thought this was a simple problem at first. Will post as soon as I have a simple test.

domeman,

It is a problem a few others have had, if you can solve it then it will help other people.

I know which side of 6mm greenhouse poly is the UV coated side if it is just coated on one side. (If I tell you then I will have to kill you as it is a closely guarded secret.)

To find wich side of Tuflite IV was supposed to be on the outside took me 6 long distance phone calls, supplier, distributer, manufacturer, and a nice guy in Alabama just after a hurricaine hit told me the poly was a three layer sandwich... UV coating on both sides.

Did I feel stupid!

Most UV Polycarbonate panel material is only protected on ONE side. If you put the wrong side toward the sun (ie: the unprotected side) the polycarbonate will decompose and deteriorate, causing the holes reported here.
We just started selling polycarbonate sheeting and our manufacturer warranty info states: "Polycarbonate sheet is treated on ONE SIDE. This treated side must be glazed outwards or towards the light source to provide protection for the substrate. If there is a need to identify the treated surface, please contact your dealer."
As a new dealer, I will find out for you.

Although we do not carry the 4mm PC, we can get custom cut 6mm panels for those interested.

Contact me if interested.

Here is a link that might be useful: UVPoly Supply

""My HFGH has UV coating on both sides.""

Please see current forum thread concerning the facts in this matter. Link attached.

Here is a link that might be useful: HFGH polycarbonate panel discussion

I have seen this question posted many times in many boards.

Greenhouse polycarbonate insulated panels are expensive. How can you tell which side is UV protected, if you get the panels mixed up?

I don't remember if anyone has a way to solve the problem. If you do, please share.

Here is what I have come up with:

1. Buy a "black light" (UV light). you can get one from $10 to $20. Or you can just buy the tube if you have a portable fluorescent light. Cheaper.

2. Steal some fabric whitener powder from your wife (or husband ).

3. Pour some whitener in the panel's cavities.

4. In a darken room, shine the black light on the panel. The clear side without the UV protection will be slightly brighter.

LED UV black light will not work very well becasue the wave length is not short enough.

dcarch

Dcarch

This seemed the obvious thing to do. And so this is what I did first. I used a UV system designed to identify minerals. Unfortunately I couldn't see any difference at all. I also tried reflecting the light to see if that helped. Again - no difference.

It could be that the harmful (to the plastic) UV is being absorbed by the first layer of the plastic even on the uncoated side. Indeed if it isn't absorbed then it would do no harm.

It is not a coating.

UV stabilizers are added to plastics. They are "dissolved" in the plastic and not coated on the surface. Think of it like mixing up jello. The color is not just on the surface, but thoughout the mix when it sets.

UV stabilizers are expensive and in a product can range between 0.05% and 5%. The more you put in, the better protection you have, but then the more expensive the panels.

If the manufacturer screws up a batch and forgets to add it, you loose all the protection. If the customer wants cheaper panels, the manufacturer can accomodate them by using less UV stabilizer. The manufacturer makes it however the customer wants - good or cheap - you can't have both.

What about a Spray on UV Coating?

http://www.krylon.com/products/uvresistant_clear/

Here is a link that might be useful: Krylon UV coating

I'm putting up a commercial greenhouse right now. New sheets of polycarbonate have a blue plastic film over the UV treated side. Coincidentally (?) I've found that this blue coloring is also visible after the film is removed.
We simply view the cut end of the sheet, and the 'outside' edge is tinted blue.

Depending upon whose polycarb you have, this may help...

I have noticed that the new twinwall I am putting on my GH has some printing on the exterior side. The brand is Palram their product name is ThermaGlas. The printing is one one edge only, in rather small type (about 1/8" tall), black, approximately 1 rib in from the edge. It has the product name, some numbers and the text "This side UV protected" The text repeats every 8' or so, so I can only find it on longer pieces.

You might want to check and see if you can find this somewhere.

HTH

^^That would be the simple and easy way to tell which side is which.

Yeah I thought that printing something to identify the UV side was a great idea.

FWIW, I took a look at a piece of my old Palram triple wall from ~10 yrs ago, and it too has this printing along one edge. So they have been doing it for a while.

I had a similar problem, with a self-assembly greenhouse, and the manual didn't say that only one side of the plastic was uv treated - until the very end, until after I had gone about removing protective covering, and inserted them willy nilly into the frame. Luckily I discovered the issue before all of them were mixed up. On my panels, the edging of the uv coated side is slightly straighter - compared to the non-treated side, which is noticably more corrugated to the touch. Hope that helps others...

I hope my solution works for you. We got some of our brand new 6mm double wall panels mixed up when we pulled them off halfway through assembling our greenhouse because of nasty weather. 1) bought a black light flashlight, like the ones they use for finding urine stains. 2) colored a thin strip of paper that will fit in the channel with a black sharpie and inserted into a channel. 3) draped black material over a saw horse and leaned the panel against it. 4) turned off the lights and shined the flashlight on the panel. On one side the black strip of paper was seen clearly, the other side it was cloudy. We got this same result for every panel. For a control group, we did the same test on a panel we had not mixed up, and the UV protected side was the side that showed cloudy. The room doesn't have to be totally dark, but it is critical that the panel is up against the black material, the strip of paper is black, and you use a black light. I don't know if using the sharpie ink to color the paper was a key factor.

UV stabilizers can be dispersed inside the polycarbonate resin or in coatings on one or both sides of the product, depending on the manufacturer. Contact the manufacturer for specifics on how they made that particular product. All polycarbonate products are not the same. UV stabilizers are expensive. The more UV stabilizer, the longer the product will last in the Sun without yellowing or cracking, but the more expensive it will be. Reference: https://advancedpolymersolutions.com/uv-polycarbonate.html 

Advanced Greenhouses, thank you the black light worked like a charm.

Quantum Black light flashlight at harbor freight - (cheap 395 nm) aim thru panel near ends. Look at side of thru plastic layer. change sides of panel. The UV side is the side where the plastics glows the most. The Non UV side will not glow much at all. Think a 365 nm would do better since the sheets reject UV beginning at 400 and the 395 nm flashlights have some output to at least 425 nm. But it works at least for Makrolon Multi UV sheets I have.

I spent a few hours on this today and I think I have the most reliable solution.

A q-tip saturated in highlighter ink with a UV light shined at it. Works in broad daylight with a cheap UV light and gives a super positive result.

Side that shines neon green is the interior side as it allows the UV to pass. Side that doesn't shine or looks violet is the exterior/UV treated side.

Future readers.. I hope you scroll to the bottom first.. I tried a lot of half baked things from this thread! 😅

The UV light did not work for me. I ended up using a different detection method I found at the link below and it worked. While not as cool or easy as the UV light method, it seems to be more reliable.

Polycarbonate UV Test with Iodine

https://www.youtube.com/watch?v=x3qT2QrlsPc

I like the iodine test but didnt have any so I tried this: I have faily thin progressive eyeglass lens that have UV induced darkening - I mean very dark. Along the sides of my panels I could get enough of the lens under each 'side' of the double wall. Pointed to the sun and tada there was a thin cleared part of the lens that was behind the side with the UV protected surface. I tested both surfaces - one does it the other does not.