Hey I'm wondering how to attach velcro tape to builders/greenhouse plastic? I have made a greenhouse and have the openings on the frame. Originally I put velcro tape on the frame and flap which worked great for a week, but now when I open it, the tape has lost it's adhesive properties and isn't attached. I could use gorilla double sided tape, but expect the same result. Could it be sewed on or some other adhesive? I thought of backing it with fabric mesh tape and stapling it. Any ideas? Thanks!
Plastic to plastic connections are often heat-bonded instead of being made with an adhesive. You might be able to literally iron them together.
You'd have to play with iron temperature settings and expect to totally melt through some plastic while testing to see what works for you.
Do this outside where the smell of melting plastic won't cause anyone any headaches.
In this case I'd pop-rivet it on, punching both materials with a leather punch, and using washers under the rivet heads. You could use webbing on the other face for reinforcement but it's quite hard to punch (a hot punch also seals the cut edges). I'd rivet both ends and the middle of the strip if it's stretched out. If it gets slack, glue or the original self-adhesive backing could be used in addition to help the materials lie together if it gets slack, with the rivets taking the load.
Sewing would also work - it's tedious by hand but might not fit under a machine.
This assumes you've got quite thick flexible sheet - I have seen rigid greenhouse plastic, which would need drilling for rivets, and sewing would require many tiny holes to be drilled - not recommended.
I have had a similar repair before, where I didn't want to puncture the plastic (a mapcase, link is to outdoors.se). The glues I tried were only partially successful.
I find the website ThisToThat useful for suggestions on what glue to use to attach different materials. You just select material 1 and material 2 and it gives you suggestions. For plastic to plastic (not PVC) it suggested either epoxy or a silicone-based adhesive (in the US, there are a range of "goop" products for repairing e.g. plastic/foam/rubber shoe soles).
I also found a big brand name plastic bonding system that appears to be cyanoacrylate (super glue) used on surfaces that have first been "painted" with an activator. They claim this works even on polyethylene and polypropylene:
The key to success is our 2 part system with activator to prime the surface prior to gluing plastic together. Works on all plastics including hard-to-bond polyethylene and polypropylene.