Which VHB to mount solar panels?

Zundfolge

1-2-4-5-3
Hi all,
I finally ordered panels and think I am going to go with VHB to mount them. I've been pouring through the archives of various forums and folks seem to use varying versions of the stuff, so I thought I'd ask here, 4950? 5952? A different one?

Appreciate any input,
Thank you,
Nick
 

Tooth Fairy

Away with the fairies.
Seriously? you are going to trust a glue to keep the panels in place at 100+ KPH?
Get some brackets, they are so much better.
 
I used 4950. So far so good. 90mph on the highway, rain, snow, cross winds.

Be very very thorough when prepping the surfaces. Use the green scotchbrite to scuff up both the aluminum brackets and the paint on your roof. scuff in a circular motion. After that, use 70% rubbing alcohol to thoroughly clean both surfaces. Apply firm pressure to activate the adhesive.
 

bstory

New member
We used 5952 to mount aluminum brackets for 2 panels in 2012 and everything is still bonded well. We have taken the van cross country 3 times and to Florida from Massachusetts twice and to Cape Breton. Lots of high wind situations - especially in southern Wyoming - snow, and rain.

I second the comment about how important prep and installation details are. Go online to the 3M website and put in the product number and you can find documentation.

We had just sanded and repainted the paint on the roof - 3 coats of rustoleum white enamel - so we just scuffed it bit - more scuffing on the aluminum. Alcohol is important. Applying pressure is hard in that location - we did one bracket at a time and I stood on the bracket for a few minutes - no good way to clamp. I even jumped up and down so there were moments of higher pressure. It was in the high 50s - low 60s the day we did it so I also applied hot air from a hair dryer for about 15 minutes after each bracket was installed.

In general, choosing the right tape depends on the hardness (or lack of resilience) in the two surfaces you are bonding. THere is a big chart on the 3M site. If the tape says for metal to metal then you are probably good - I don't think the paint is much of an issue - it is how much give there is in the underlying surface - but that is my reading of the 3M documentation. You may want to review this yourself. I don't remember why I chose the 5952 over the other options, but I do remember that some of the difference in numbers reflects different thicknesses, widths, colors, etc...
 
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hein

Van Guru
McMaster Carr has a variety of VHB tapes and a description of their use.
http://www.mcmaster.com/#3m-vhb-tape/=14dntb1

A great way to get more holding power from VHB is to increase the surface area. That is why we make our pads. This also makes it easier to remove the panel by unbolting the bracket from the pad. Most brackets are attached to the bottom of the panel which makes getting to those fasteners sort of difficult to access once mounted on the roof.

We have great confidence in VHB but do prefer attaching to the OEM roof rails.
 
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autostaretx

Erratic Member
If you have a white Sprinter, just remember that the VHB is only adhering to MB's "wonderful" paint job....

...as the earlier notes say: proper surface preparation is the key ... and i'm not sure how far i'd trust the white paint as "proper".
(as a first step, i'd (or "i'll", since solar is in my future) use twice the "normal" surface area of adhesion... think 6 or 8 brackets instead of 4)
((in truth, my plans are VHB brackets, but with the front two also having a screw or two to prevent having the leading edge of the panel even thinking about "lifting off" in the breeze))

--dick
 
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Zundfolge

1-2-4-5-3
Yes, I've poured over that hefty document of VHB info, sifting through varying material energies etc. and then I thought, "hey, why not ask someone who's already done it?" Hence, me, here, and this.

So far one vote for 4950, and one for 5952. Sounds like those are the two that are commonly used and not one has reported a problem.

As much as I'd also prefer mounting to roof rails, T1N's don't have that luxury.

Much prep will be done, thank you all for the info!

On another note, pass throughs: I was almost set on using cable clams but they're kind of goofy, and I happened upon these.

https://www.amazon.com/gp/product/B...6_4?ie=UTF8&psc=1&refRID=ZY8NN9QTJKVAP5C34CRV

Anyone have any experience with them? They seem to be well enough constructed, and I'm likely to use them, but would like to hear if anyone has any thoughts?

Thanks!
 

calbiker

Well-known member
I used 4950 10 years ago. Still holding up well. My roof is fiberglass. Each pad has 24 sq in of surface area. The panel is tiltable. It has seen some pretty good wind in the tilted position.
 

Attachments

Midwestdrifter

Engineer In Residence
T1Ns can have very poor paint adhesion, see below.

In case anyone was wondering, T1N Sprinter Paint is crap. I knew it wasn’t the best, but my recent experiences outline its poor adhesion. An example is the solar panel brackets on my van. The photo below is an intermediate bracket. These were attached with 3M VHB tape and sealed with clear silicone. In less than 1000 miles the paint to primer bond failed completely.



The rear brackets were bonded with 3M 5200 adhesive and are still just fine after 10,000 miles. :idunno:
 

Zundfolge

1-2-4-5-3
T1Ns can have very poor paint adhesion, see below.



The rear brackets were bonded with 3M 5200 adhesive and are still just fine after 10,000 miles. :idunno:
Wow. That I haven't seen before. Thanks for that, we all know how crappy the T1N paint is, but that's the first instance I've see of that. I recently had my pass window crash wrapped for a couple of days waiting for a replacement window, and the crash wrap pulled off a bunch of paint on the door frame, so I'm not too surprised.

I believe what I'll do is put 1 screw in each bracket at the leading panel edge, as a safety against what you just showed us. Cheap insurance considering the brackets will be sealed with Dicor anyway, so I'm not worried about leaks.

Thanks again!
 

Midwestdrifter

Engineer In Residence
Personally, if you are going to use a screw/fastener, I would switch to a urethane adhesive such as 3M 5200 or sikaflex 200 series. The adhesive will seal the screw penetration and adhere the bracket. You will have one less step and material compared the the VHB. Once you add a penetration, you need to use sealant. over the screw head.

The biggest appeal of the VHB in my opinion is that it can be removed without leaving any trace. Once you eliminate that feature it has minimal advantages over the other adhesive options.
 
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hein

Van Guru
These were attached with 3M VHB tape and sealed with clear silicone.
Could the silicon have contributed to the failure? Some produce acids during cure. I do agree there appears to be a paint adhesion issue on the T1Ns. I don't believe the VHB contributed to that. Perhaps the leading edge brackets undergo more vibration and cyclical (up/down) loading.

VHB is a great companion to screws, imo. It seals and provides vibration resistance and to some extent a thermal block. There is no messy wet state or cure time required although the bond strength does improve in about 24 hours. Prep, peel, stick, screw (optional), done. VHB has been good for me. Follow this link to a search for VHB in our build: https://sprinter-source.com/forums/search.php?searchid=2659442

Any roof mounted accessory deserves periodic inspection (driven in wind lately?) including a manual pull/push/tug test. It is unlikely although not impossible that all connection points will fail simultaneously.
 
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Midwestdrifter

Engineer In Residence
I strongly doubt it was the silicone. The paint to primer bond is just junk. :idunno:

On normal quality paint the VHB would have performed great. The reason the VHB failed and not the adhesive (on my van), is because th VHB is thinner than the adhesive, and as such is more likely to intitate the peeling effect that the T1N paint is so weak against. Seriously, automotive masking tape can remove the weaker areas of my vans factory paint!

I am a fan of VHB tapes myself, lots of excellent applications.

The cure times of adhesive sealants are a consideration, the faster cure versions are usually usable in 24-48 hours depending on temps, bond thickness, and primer usage. If you use them in conjunction with mechanics fasteners, you can usually cut that time in half.
 
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I'm planning to use some 8020 as framework to connect all of the panels together, and attach feet to the roof with VHB. I'll use one set of 1/4-20 bolts at the front, just to make sure everything stays put. I think this is a good middle-ground. Only two holes in the roof and pretty much no chance of failure.

Noteworthy: 3M recommends never attaching VHB to paint, but only attaching it to bare metal with very specific prep. They advise 72 hours at 75 degrees F for the material to flow and achieve full bonding.
 
I found this video really helpful for learning about various sealants. It doesn't address VHB, but perhaps it's helpful to someone else, like myself, looking to learn more about roof sealant options. 3M 5200 and 4000 are addressed at around 7:00. I'd never heard of either before, so thanks to Midwestdrifter for mentioning them.

https://www.youtube.com/watch?v=G-aQzoHqM80
 

Zundfolge

1-2-4-5-3
Thanks for all of the feedback everyone, I am tempted now to use the 5200 in place of the VHB, but I've already got everything on order and it seems that there is enough documented success with it. Gonna do 1 screw on each leading edge fastener for redundancy's sake.

Now I'm thinking though, maybe I oughta sand down to bare metal right where the brackets will go? Since it'll all be covered with lap sealant afterwards it will be anaerobic and *shouldn't be prone to any rusting, has anyone done this?

Since I've seen that paint/primer bond fail on my van due to automotive masking tape, I'm real hesitant about trusting it with wind-loaded panels...
 

autostaretx

Erratic Member
Gonna do 1 screw on each leading edge fastener for redundancy's sake.
Should i comment that a single sheet metal screw may not be adequate?

You really want something with a nut and washer on the inside surface of the metal, (or a Moly-like anchor).
More than one screw might suffice (if you periodically check that they're still tight).

--dick
 

Jackies Dog Grooming

2016 NCV3 144" 4 banger
1/4" riv-nuts and lock-tight on the bolt threads seems like a one and done situation. Of course a dab of silicone around the hole between the roof and bracket before inserting the bolts would reduce the possibility of leaks.
 

Cheyenne

UK 2004 T1N 313CDi
Of course a dab of silicone around the hole between the roof and bracket ...
It is bad practice to use RTV Silicon on steel or aluminium (UK spelling) panels as the Acetic acid released during curing attacks the metal. Use a non-setting caravan or RV mastic.

Keith.
 

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