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From: John De Armond
Subject: Re: Cheap DIY solar collector
Date: Fri, 29 Aug 2008 17:39:31 -0400
Message-ID: <>

On 29 Aug 2008 15:48:35 -0400, wrote:

>>   I think 3M # DP-8005 is the recommended adhesive, I don't know about
>>Scotch-Weld 4693 H, it may be fine.
>...3M recommends it for polypropylene. It comes in a $15 red and white tube.
>I made a heat exchanger by gluing up multiple coroplast sheets separated by
>small coroplast spacers into a brick.

Here's what Coroplast has to say about bonding the stuff:  Bottom of the page.  Welding isn't difficult
to do using supplies from  Harbor Freight sells
a decent hot air plastic welding gun.

Be sure to note the part about the corona surface treatment.  ALL PP cement
requires that the PP be surface-treated to increase its surface energy.  The
three major methods are flame, corona and ion bombardment, in order of
increasing effectiveness.  As I understand it, the process embeds ions in the
surface to make the surface more attractive to the cement.  The surface
treatment leaks off and has to be repeated if the material is stored for long.

I've never tried to cement Coroplast but I have cemented PP sheeting to make
tanks.  I used the flame treatment because that's the easiest one to do in the
shop.  This involves making a highly oxidizing flame on an acetylene torch,
preferably with a rosebud head but the cutting head can be used.  The flame
needs to be just on the edge of blowing out.  This flame is rapidly passed
back and forth across the area to be cemented.  It can NOT be allowed to melt
the plastic, as that drains off the charge.  The treated area has a slightly
duller look than the adjacent plastic.

The flame treatment method only deposits a little surface energy and it
doesn't stick around long so it must be done right before cementing.  Corona
treatment lasts longer but is much more difficult to do in a general sense.  I
have read that very intense, very short wave UV bombardment will do the same
thing as corona treatment but I've never had the opportunity to try it.

At various points on that web site they refer to it as a PP copolymer and as a
polyolefin copolymer.  I've written them asking for a clarification.  It may
be a blend.

I have also asked for UV data on the standard product.  If you look at the
product specifications, you'll see that UV-resistance is an extra-cost option.
I also asked if color makes a difference in UV-resistance.  The MSDS lists
carbon black as the pigment for the black product so it very well may be more

Note that there is a sound-alike knockoff called CorPlast

Given that this stuff is made in Malaysia, I imagine that it's considerably
cheaper than Coroplast.  I have no idea of the difference in quality or
properties, if any.  I do know that in the sign biz, the generic term is
"Corplast".  The "o" is dropped.  I've dropped a note to my sign supply
company asking them which they sell.  I just bet that if you walk into a
plastics supply house and just ask for "Corplast" without specifying the brand
name, that you'll get the foreign made stuff.

The Cor(o)plast that I buy from my sign supplier lasts less than 2 years in
direct sunlight.  That's about how often that I had to make new signs for my
restaurants.  Since I could make the signs myself, it was still cheaper than
going to a higher quality substrate.

I can't imagine investing the kind of time y'all are talking about with a
material that breaks down that rapidly.


From: John De Armond
Subject: Re: Cheap DIY solar collector
Date: Thu, 04 Sep 2008 17:51:04 -0400
Message-ID: <>

On Tue, 26 Aug 2008 10:35:27 -0400, Neon John <> wrote:

>On Mon, 25 Aug 2008 16:18:48 -0700 (PDT), Jim Wilkins <>
>>I was wondering how well that stuff would work in a solar collector.
>>TekSupply sells it for greenhouse covering but it isn't cheap.
>Works like crap.  This isn't the greenhouse glazing.  Coroplast is that cheap
>signboard used to make political and other short-lived signs.  If you listen
>closely you can hear it decompose when sunlight shines on it.  Painting it
>black will help a little with the solar degradation but it won't stop it.  If
>that thing lasts a summer, I'd be quite surprised.

Several folks seemed to disagree with my experience-based advice relative to
Coroplast.  I did something almost unheard of on Usenet.  I wrote to Coroplast
to get authoritative information.  I got a response from their Manager of
Process Engineering.  I've asked permission to post his entire reply but in
the meantime, here are the nuggets.

"Coroplast(R) is a polyolefin copolymer.  The Polyolefin copolymer is
composed of approximately 95% polypropylene and 5% polyethylene.  The
polyethylene is added to improve flexibility and other physical

As we who work with the stuff already know, polyethylene cement will not work
with it.

"We do not guarantee any expected life of the standard product.  However,
I believe that you could expect from 8 months to 12 months of life
during normal outdoor exposure."

There you have it from the horse's mouth.  Almost exactly what I said in my
original post.

I asked whether highly pigmented versions such as black would last longer.  He
says that the pigment stops the penetration of UV so the web and reverse side
remain flexible but that the side exposed to light deteriorates at about the
same rate.

I've written back and asked about their UV inhibited product.  The web site
makes me think that it is a special run item with large minimum order
requirements.  We'll see.


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