VHB Purpose, Price, and Alternatives?

[CarlCruzin]

I am considering using VHB tape for an upcoming project, but am finding that it is quite expensive! For 2" wide it is about $5/ft and I'm going to use potentially 80'.
(adhering unistrut to the fiberglass roof of my rv for solar panel mounting)
I'm not trying to spend that much on tape, so that brings me to my next question. Why is everybody using VHB? Is it just for the convenience and minimal mess?

I'm considering switching to a construction adhesive, which I could probably do the project with a few tubes for a lot less. Is there any reason why I should consider sticking with the VHB?

 

[Loadtoad]

Why not cut the unistrut into smaller sections and put just them where the solar panels will mount? You don't need to mount a complete unistrut rail just to put 3 tie down points for each side of a solar panel? You will save a lot of weight also.

 

[Mdb]

The real stuff is expensive but works. Like have to remove it with a hammer and chisel works!
Buy once, cry once applies here. Use the VHB and rest assured your struts will stay attached.
Recently I bought 80ft of VHB off of Amazon. Turns out it was counterfeit. Painters tape was stronger!

 

[CarlCruzin]

Why not cut the unistrut into smaller sections and put just them where the solar panels will mount? You don't need to mount a complete unistrut rail just to put 3 tie down points for each side of a solar panel? You will save a lot of weight also.

The main reason I was considering running the whole length is for more adhesive contact area.

The real stuff is expensive but works. Like have to remove it with a hammer and chisel works!
Buy once, cry once applies here. Use the VHB and rest assured your struts will stay attached.
Recently I bought 80ft of VHB off of Amazon. Turns out it was counterfeit. Painters tape was stronger!

I'm sure it works, but I'm wanting to consider alternatives since spending $400 on adhesive tape seems crazy to me. That doesn't surprise me about amazon. I've heard some of the weirdest things being counterfeited.

 

[MrNatural22]

I used Sikaflex 221 to attach my panel mounts. Holds very well as long as you follow all the surface prep instructions. I used 92% alcohol to clean all surfaces. But I also attached vinyl covered steel cable tethers to the panels for peace of mind. Always a good safe idea even when attaching panel mounts with screws.......No regrets
Amazon carries Sikaflex.

 

[Loadtoad]

This is how I did it.

 

[12VoltInstalls]

Why is everybody using VHB? Is it just for the convenience and minimal mess?

I don’t know.

Boggles my mind. Then they seal around it ‘to be sure.’

Do outfits install solar on roofs with vhb?
Nananana no.

People are afraid to drill holes and/or have manufactured item dependency. I think vhb is dangerous myself.

I have installed solar panels, racks, antenna brackets, lighting, planer mast bases, transducers, tie-downs, RV vents (not replacements), skylights, aircon…. No misplaced holes, no leaks, and no vhb.

3M 5200 or polyurethane caulking is permanent, stronger bond than vhb, and waterproof. Leveling lap sealant isn’t exactly the most structural thing but it is a good sealant. But everything gets bolted; boats, cars, trailers, RVs.

 

[kjswiley]

People use it because it works. I have no problem drillings holes into a roof that has a giant AC and fans/skylights etc. That said, I did use VHB for my roof rack on the truck camper shell, and it works fantastic. I also bought a very small can of the primer made for VHB, I do not know that it is needed or not, but my connections are rock solid on the fiberglass shell.

It did not work at all on my Raptored TPO Rubber Roof though, unsure if it is due to the texture or composition of the raptor bedliner.

 

[12VoltInstalls]

VHB for my roof rack on the truck camper shell, and it works fantastic.

While I suppose bolts can randomly fail they don’t fail.
VHB as a structural connector is insane to drive down the road with panels or ladders or kayaks that can fly off and kill somebody. There’s no torque spec for vhb and load, temperature varies its strength in tension and shear.

Never mind the moral side, negligent homicide will give you an opportunity to meet a bubba and make new friends.

 

[Whinny]

One thing that concerns me with long unistrut mounts is the nice "dam" they make. RV manufacturers put that arch in the roof so water can run off without pooling. If you wish to use unistrut mount it on brackets that are attached to any roof rafter it passes.

 

[kjswiley]

While I suppose volts can randomly fail they don’t fail.
VHB as a structural connector is insane to drive down the road with panels or ladders or kayaks that can fly off and kill somebody. There’s no torque spec for vhb and load, temperature varies its strength in tension and shear.

Never mind the moral side, negligent homicide will give you an opportunity to meet a bubba and make new friends.

I do not disagree, but I would wager the bolts rattle loose before that tape fails (the locktight and locking nuts will stop that). I check both often.

 

[12VoltInstalls]

I would wager the bolts rattle loose before that tape fails (the locktight and locking nuts will stop that). I check both often.

That would be a bet lost.

Properly torqued bolts sustain aircraft jet engine mounting, wheel lugs on your car, high-tension line tower bases, suspension bridge members, the connecting rods and main journal caps in engines, and high-rise building crane rotators.

Ever watch a big sailboat at 20 knots in a 15 knot wind? There’s a ton of power in wind.

And when your 230W panels BOLTED to unistrut scotch-taped to a plastic roof fly off at 65 mph and hit the minivan behind you on its way to a birthday party…. I actually want to swear and unleash a verbal onslaught.
But you’ll probably make the 6 o’clock news!

 

[kjswiley]

That would be a bet lost.

Properly torqued bolts sustain aircraft jet engine mounting, wheel lugs on your car, high-tension line tower bases, suspension bridge members, the connecting rods and main journal caps in engines, and high-rise building crane rotators.

Ever watch a big sailboat at 20 knots in a 15 knot wind? There’s a ton of power in wind.

And when your 230W panels BOLTED to unistrut scotch-taped to a plastic roof fly off at 65 mph and hit the minivan behind you on its way to a birthday party…. I actually want to swear and unleash a verbal onslaught.
But you’ll probably make the 6 o’clock news!

Well you should not use scotch tape.


I never said it was fool proof, but here is an example of mechanical failure:
"A full size semi-truck with a sleeper cab was constructed with all exterior panels
and doors taped to an underlying frame with 4950 VHB Tape. After approximately 500,000km on
the harsh durability track the VHB Tape bonds remained completely intact. This is particularly
impressive as some of the mechanically joined and welded parts failed and required repairs during
the test program."

https://multimedia.3m.com/mws/media/764998O/iatd-product-info.pdf

 

[CarlCruzin]

That would be a bet lost.

Properly torqued bolts sustain aircraft jet engine mounting, wheel lugs on your car, high-tension line tower bases, suspension bridge members, the connecting rods and main journal caps in engines, and high-rise building crane rotators.

Ever watch a big sailboat at 20 knots in a 15 knot wind? There’s a ton of power in wind.

And when your 230W panels BOLTED to unistrut scotch-taped to a plastic roof fly off at 65 mph and hit the minivan behind you on its way to a birthday party…. I actually want to swear and unleash a verbal onslaught.
But you’ll probably make the 6 o’clock news!

Those are some pretty charged statements.

We discussed this in another thread to some extent, and I don't see much of a point to doing so here also. But here are my thoughts:

Aerodynamics: You speak of a sailboat, which has a sail that is designed to be perpendicular to wind and catch as much as possible. If Solar panels are secured to a roof with at most a 1" x 32" opening under the front, how much lift could the wind generate? even at 100mph? Secondly, if that air gap were blocked is there any way that the wind could generate lift on the panels? If wind can only hit the front 2" of a panel, and the top of it, then there is no way that lift can be generated. I am not aerodynamic engineer, but that is a pretty basic concept.

With that being said, I will likely supplement with some mechanical fasteners. Not because I think it would need it in 10 years or 100k freeway miles (with normal frequency inspections), not to satisfy internet forum users overly cautious criticisms, but because the overkill measure of mechanical fasteners is worth the minimal effort added.


Back to the original subject of the thread:

I used Sikaflex 221 to attach my panel mounts. Holds very well as long as you follow all the surface prep instructions. I used 92% alcohol to clean all surfaces. But I also attached vinyl covered steel cable tethers to the panels for peace of mind. Always a good safe idea even when attaching panel mounts with screws.......No regrets
Amazon carries Sikaflex.

Thank you for the recommendation, I will look into that. It seems that polyurethane adhesive is a very durable and significantly less expensive option for the scale of my project.

 

[kjswiley]

Those are some pretty charged statements.

We discussed this in another thread to some extent, and I don't see much of a point to doing so here also. But here are my thoughts:

Aerodynamics: You speak of a sailboat, which has a sail that is designed to be perpendicular to wind and catch as much as possible. If Solar panels are secured to a roof with at most a 1" x 32" opening under the front, how much lift could the wind generate? even at 100mph? Secondly, if that air gap were blocked is there any way that the wind could generate lift on the panels? If wind can only hit the front 2" of a panel, and the top of it, then there is no way that lift can be generated. I am not aerodynamic engineer, but that is a pretty basic concept.

With that being said, I will likely supplement with some mechanical fasteners. Not because I think it would need it in 10 years or 100k freeway miles (with normal frequency inspections), not to satisfy internet forum users overly cautious criticisms, but because the overkill measure of mechanical fasteners is worth the minimal effort added.


Back to the original subject of the thread:


Thank you for the recommendation, I will look into that. It seems that polyurethane adhesive is a very durable and significantly less expensive option for the scale of my project.

You would also be hit with crosswinds, so with that theory would need to block more than just the front.

 

[rmaddy]

If Solar panels are secured to a roof with at most a 1" x 32" opening under the front, how much lift could the wind generate? even at 100mph? Secondly, if that air gap were blocked is there any way that the wind could generate lift on the panels? If wind can only hit the front 2" of a panel, and the top of it, then there is no way that lift can be generated. I am not aerodynamic engineer, but that is a pretty basic concept.

You don't just need wind going under the panels to push them up. Wind going over the top of the vehicle can create a lower pressure on top of the panels. This lower pressure can pull the panel up.

 

[12VoltInstalls]

particularly
impressive as some of the mechanically joined and welded parts failed and required repairs during
the test program."

A) that is not a valid comparison from an engineering perspective for at least four reasons this welder but not engineer can think of.

B) VHB is not useless- but its availability to and discovery by the masses has led to it being used in manners and applications I do not believe to be safe- like in place of structural components where moral sense and liability dictate otherwise.
I believe VHB may be acceptable to affix a solar panel or other items to a building, perhaps, and do so securely, depending on a number of factors.
However… If it doesn’t have a rating after meeting sae, osha, astm, etc. test procedures it shouldn’t be used where life safety is a factor of consideration.

The thing is it’s not really that hard to simply find the structural elements in the roof and attach to those. Yes, RVs are a pain in this regard but as someone that’s cut holes in roofs, boats, showers, tanks, and floors for a lot of years i can say for sure it’s not hard.
If you can figure out how to diy a solar power system you can figure out how to safely mount it.

 

[jberger]

You can ask 3m directly about the proper application of VHB here: https://www.3m.com/3M/en_US/vhb-tapes-us/applications/transportation/

 

[12VoltInstalls]

ask 3m directly about the proper application of VHB

for proper application of is discussed in their guide. Good shear properties.

No mention of any applications of materials in tension with loading.

 

[jberger]

That link lets you ask the 3m technical engineer directly. If I had the time, I'd write up both the Z Bracket and Unistrut Panel Mounting details and ask them to validate it.

Personally, I'd always want to use mechanical fasteners. I can just hear the attorney asking me if I really expected those panels to stick on some foam tape. No data sheet is going to get you sympathy in that case.