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Posts: 2,952
Reply with quote  #31 
Verrrrrry Interesting!
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay


Posts: 1
Reply with quote  #32 
It's now late June 2016. Did anyone ever find a reliable way to create a waterproof bond to coroplast? like many of you, I've thought of this material for this purpose for ages, but the bonding has always kept me from bothering.

Posts: 3
Reply with quote  #33 
As you know some adhesives stick to polypropylene (coroplast) but the bond is weak. So I will be trying a
different tack: to work with the weaker bond by using larger bonding areas and mechanical interlocking. I have
found the old fashioned type of contact cement made with neoprene rubber works quite
well and also the regular "35 year" exterior silicone caulk although less strong might

To get a better joint I will be using a big header pipe (1 1/2 inch ABS) I want to try
removing the first 3/4 inch of the fins inside the coroplast then splaying out the
walls forming two flanges one to each side at almost 90 degrees. Sliding the flanged
part into the slotted header pipe and using silicone caulk between the pipe and
the flange. Then using a jig inside to keep the flanges pressed to the header pipe
until the silicone cures. Then using a jig inside to keep the flanges pressed to the
header pipe until the silicone cures or leaving the jig in place ensuring pressure to
hold the parts together.


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Posts: 1,074
Reply with quote  #34 
Looking forward to hearing the results of your plan.
Both temperature rise and airflow are integral to comparing hot air collectors

Posts: 3
Reply with quote  #35 
While slow I am making some progress. I have got a small panel working without leaks using the method described below. I used the general purpose Silicone caulking Home Hardware brand (Canada) (vinegar smell) which is rated for 35 years and recommended for aquariums.

Initially I had two tiny leaks but I am using some prestone stop leak and so far so good. Also the first try was too much prestone and I will cut the dose in half the next time. Don't know if the anticorrosive additives will play havoc with the ABS header or the silicone caulk. Only more testing will tell.

I am using 1.5 inch ABS pipe for header, 10 MM thick black coroplast for the absorber. I make two cuts on the table saw to cut out the internal fins of the the coroplast sheet. Then bend the resulting legs outward. I cut a 10 mm grove in the ABS pipe with two cuts on a table saw. A surprise byproduct is a strip of ABS pipe that I glue along the length on the outside of a 1 inch PVC conduit. After I lay a thick layer of the silicone caulk on each side of the coroplast I slip the ABS pipe along the coroplast then use the PVC conduit as a jig to hold the splayed legs of the coroplast against the inside of the pipe. I wait about an hour and a half then twist the conduit and remove it from the inside of the header. Then let the silicone cure for at least 24hours

Once you cut the pipe, it contracts in diameter a bit (I guess due to residual stresses when it was extruded) Instead of using the usual ABS pipe cement I used the same silicone caulk for the header end cap and the ABS pipe to threaded adapter at the other end of the header. I did this since these pieces still have to be sealed to the Coroplast sheet as well as to themselves.

The black coroplast is a bit shiny so will be using the Krylon Camouflage Ultra Flat paint on the front of the collector to improve performance. I tried this already on another test collector using the 10 MM black coroplast and the paint adheres very well and is amazingly pitch black.

I just tested this panel today for about two hours. Next step is to get this collector back out in the sun to expose it to heating and cooling cycles and see how well the silicone caulk stands up.

100_2547.jpg 100_2565.jpg 100_2561.jpg 100_2556.jpg 


Posts: 31
Reply with quote  #36 
I know this thread is pretty old, but thought I might put my 2c in (worth about 1/3 of a US cent at todays exchange rate).

The issue with PP is that they are LSE (low surface energy) plastics - which is why they are attractive for their intended use. Both polypropylene and polyethylene are polyolefins: https://www.materials-talks.com/blog/2017/03/26/what-are-polyolefins/.

In order to bond them, you need to activate the surface - usually done in the hobby field with a low flame. Other ways are to use a surface activator, or primer.

That's usually a silane or hexane in some sort of vaporising carrier. Most common primers are designed for cyanoacrylate (superglues) adhesives and made by the major superglue manufacturers, like Loctite, 3M, etc., but will 'prime' for any suitable adhesive.

Loctite has their 7701 primer, which after application will allow a solid bond by most silicone and other caulks.

Without a primer, heat-activation, rubbing alcohol and fine sanding of the bonding surface, with an ACRYLIC caulk (not silicone!) will make a good, permanent bond. Something like 3M Marine Adhesive Sealant 5200 ticks all the boxes, bit only has a working temperature of 88C, and latex caulks are also no good at higher temperatures. 3M makes a range of heat-resistant acrylic caulks which are designed to seal fireboxes, etc. but are the foaming type and less useful as an adhesive. One other potential is an adhesive transfer tape, like 3M 966. Takes temps up to 232C, huge shear strength even at high temp and will definitely hold primed PP. 

So, a two-part solution - either primer and caulk/adhesive or mechanical prep and transfer tape/caulk. Adhesive for the mechanical bond, caulk for the sealing.

I don't think you will get one product to do both jobs.

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