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Old 03-19-2015, 05:17 PM   #1
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Which VHB tape?

I'm about to attach the new solar panel and I had learned about the 3M VHB tape here on the forum. When I went to order it I learned there are many different versions of the VHB tape. Which one to select depends on the "surface energy" of the bonding surface. Unfortunately they don't define the "surface energy" for fiberglass, so I'm at a loss.

Am I over-analyzing this (been known to do that!), or does it really make a difference? Any suggestions on which VHB tape works best with a fiberglass roof are most appreciated.

Brad
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Old 03-19-2015, 06:20 PM   #2
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Re: Which VHB tape?

I've just been researching this. I always over-analyze I have more notes but no time to type it up at the moment.

Short version:

There are three variables in the tape:

1) Adhesive type
2) Foam firmness/conformability
3) Tape thickness

Then in the material to adhere too, there is the "energy" of it (seems to be related to hardness vs. plasticity for the most part), and the relative flatness of it.

VHB 4941 Seems to be the "all purpose" VHB that many use. Multi-purpose adhesive and conformable foam.

VHB 4950 May be what AM solar uses (but not sure). We used this on buddy's SMB and so far so good (one 1,500 mile drive in pouring rain and hot to freezing temps done so far). General purpose acrylic adhesive, firm foam.

VHB 5952 The favorite of the 3M tech support fellow for my description of use (aluminum angle feet to polyester-resin gelcoated fiberglass). Modified acrylic adhesive, and very conformable foam.

Tech did also mention that 4941 would also be "fine."

1.1 mm seems to be the right thickness (is also the most common).

I'll write more detail later (presuming I see some in my notes!), but also interested to see what others have to say.

I have seen all three of these noted as being used in RV roof installations with success, btw (Googling/reading).
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Old 03-20-2015, 09:36 AM   #3
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Re: Which VHB tape?

......You are probably over-analyzing it a bit.

I use VHB tape now and then in the products I design, and typically I'm thinking about how thick the foam layer needs to be (conformability) and how wide the tape needs to be. If there is no width constraint, use wide tape, like 3/4".

The stuff is amazing, and somewhat permanent......buy some and stick a small piece to a clean surface, then stick another clean surface to the piece, press firmly and wait and hour or so......good luck getting the joint apart.

You can get it apart by running a piece of music wire (ie guitar upper E string) through the foam in a sawing motion, then cleaning up the goo with brake cleaner or other solvent.


http://www.mcmaster.com/#vhb-tape/=we42mw


....this may be obvious, but make sure everything is in it's happy place before sticking the items together, as it's quite difficult to reposition. If you do a very light touch you can sometimes un-stick and reposition quickly, but once the adhesive sets up for a few minutes it gets tough.
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Old 03-20-2015, 11:52 AM   #4
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Re: Which VHB tape?

Quote:
Originally Posted by boywonder
......You are probably over-analyzing it a bit.
Me?

Well I suppose; but on the other hand, I figure if they make a variety of kinds, one or two must be better (or worse) than the others for this job. And I have to pick one. I like to understand why I'm choosing one vs. another. Also because I'm considering it for some other uses, I needed to get a general understanding.

The 3M technical document is really helpful (vs. a few of their "pretty" ad type documents that really weren't all that useful). It just took me a while to get past the density (not that I am all the way "past" that yet).

At any rate, my notes above basically cover what I know (although I was in a hurry when I typed it). The two tapes recommended by the 3M tech person for this job were either 4941 or 5952.

4941 leans more toward high surface energy and perfectly flat mating surfaces.

5952 also does high energy surfaces, but then leans more toward medium surface energy items as well (the adhesive) and less perfectly flat surfaces (the foam).

I think either would likely work fine - the 3M tech indicated such too (with a slight preference for the 5952 due to the one molded/gelcoated surface).

IIRC, I chose 4950 for my buddy's SMB (when I had only done a "normal" amount of researching ... gasp) and it has held fine so far. It would be to the "other" side of 4941 from 5952, in a way (extending less into the medium surface energy part of the scale). What I didn't realize at the time was that our gelcoated fiberglass (more specifically polyester resin) was lower in "energy" than, say, epoxy resin/fiberglass. They list the latter as higher energy, but then something like a two part polyester paint as medium energy -- so apparently polyester fiberglass is more mediumish. It's not way down there, but just lower than the high of aluminum or similar. For the roof of a painted van, 5952 would definitely be recommended (and not 4941) because polyester type paint is more toward medium energy. We can apparently use either one on a gelcoated fiberglass/aluminum bond. But since polyester/gelcoat is somewhere in the middle, the tech person leaned slightly toward the 5952, but also said the 4941 should be fine. 4941 is slightly less tolerant of high heat, but 5952 is only a bit better (200F vs. 250F, although either can stand more for short periods).

The tech recommended the 1.1mm thickness based on my description of the fiberglass surface (aluminum angle was obvious of course).

So just to recap, if anyone is still awake or cares

1) Check the two surfaces that are being bonded to see where they fall on the high energy to low energy scale (essentially high energy is hard; low energy is soft). 3M has charts in their tech document. This directs you to a particular adhesive type (there are three or four).

2, 3) I'm not actually totally clear on how these two differ from each other, but there is foam type (firm, conformable, very conformable), and foam thickness as two different factors. I think they both have to do with how "flat" the surfaces are, but haven't quite grasped the subtle differences. Maybe the foam type is more to do with the energy of the surface.

At any rate, I'm going to go with either 4941 or 5952, in the 1.1mm thickness.

Prep is likely the most important (as always, even though for some reason it is the least exciting).
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Old 03-20-2015, 02:44 PM   #5
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Re: Which VHB tape?

Timely post - I'll be putting a flexible panel on soon as well.

When taping down a panel, are people doing all four sides and then maybe a strip in the middle? I was considering leaving the back side open. I have also considered just using the VHB tape on the leading edge and then using industrial velcro on the sides to make removal a little more realistic down the road if needed.

I suppose if I had a solar panel failure I would even consider leaving the old one and just mounting the new one right on top.
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Old 03-20-2015, 02:53 PM   #6
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Re: Which VHB tape?

Quote:
Originally Posted by rockbender
When taping down a panel, are people doing all four sides and then maybe a strip in the middle? I was considering leaving the back side open. I have also considered just using the VHB tape on the leading edge and then using industrial velcro on the sides to make removal a little more realistic down the road if needed.
I think if you applied it around all 4 sides and a strip down the middle you can probably pick up the van by the solar panel.........which would actually be picking the van up by it's paint if you think about it.
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Old 03-20-2015, 02:57 PM   #7
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Re: Which VHB tape?

Quote:
Originally Posted by sbgrimm

Am I over-analyzing this (been known to do that!), or does it really make a difference?
Viva: I was referring to sbgrimm's comment above......but your in depth research is appreciated!

I think the "conformable" part just has to do with the thickness of the foam. If you use the real thin stuff on wavy surfaces, you don't get full contact, even after pressing pretty hard.

......I would consider the PH top as a wavy surface......

For anyone who has never used VHB tape, just buy a small roll and try it out on some scrap materials. It'll give you a good indication of what it can and cannot do pretty quick.
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Old 03-20-2015, 05:17 PM   #8
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Re: Which VHB tape?

Quote:
Originally Posted by boywonder

I think the "conformable" part just has to do with the thickness of the foam. If you use the real thin stuff on wavy surfaces, you don't get full contact, even after pressing pretty hard.

......I would consider the PH top as a wavy surface......
I agree that these are somewhat inter-related. That said, there are varying thicknesses of foam with all of the foam types (firm, conformable, and very conformable) so you can mix variables. The 3M tech sounded pretty "yep" on the 1.1mm thickness for this type of job, but allowed as how either the 4941 or the 5952 would be appropriate (with a slight lean toward 5952). Both would be 1.1mm thick, with the 4941 having conformable foam and the more high energy adhesive (that will also do medium to some extent), and the 5952 having very conformable foam and the high to medium energy adhesive that leans more toward the medium.

And yeah, in the scheme of things our "flat" molded fiberglass is not really all that flat.

I'd use 5952 for sure on paint, for this I waffled and ordered both 4941 and 5952 just now. I'm sure I'll find uses for the "other" one. Or maybe use some of each and have a living experiment

Note that I was asking him about an installation that has me mounting 3/16" aluminum angle to gelcoated fiberglass (rigid panel) -- not a flexible panel (which would likely be more medium to low energy I think?).

Sorry I mis-read your friendly "poke." I guess I'm too used to being on the defensive about being overly analytical
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Old 03-20-2015, 07:06 PM   #9
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Re: Which VHB tape?

The thicker foams will also help if the glued joint is in shear, like when your solar panel and PH roof are bouncing up and down when driving down a fire road.

The foam adds compliance to the joint when shear loaded so the glue joint won't pop.
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Old 03-23-2015, 04:20 PM   #10
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Re: Which VHB tape?

Thanks, Viva, for schooling us on the relative merits of each of the VHB tapes. I just ordered the 5952. I think a little over-analysis is justified for an application like this. Like you said, they make several different versions for a reason, and when you have roughly 16 square inches of adhesive holding a 26 lb panel at 75 mph you want the best stickum you can get.

Being a belt and suspenders sort of guy, I ordered 2 sets of the Renogy mounting brackets in case I want to add 2 more in the middle of the panel. And I'll probably screw down any brackets that are outside the PH canvas in addition to the VHB.

BoyWonder: good tip on VHB removal using the metal guitar string. Hope I never need to try it.

Brad
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