21 replies to this topic

[BillTheHiker]

I bought the 100 watt panel kit with self-adhesive rocker feet so I would not need to put screws into the roof. The claim the VHB tape makes a very strong connection.

 

 One concern I have is the painted aluminum roof. AM Solar has a video demonstrating the installation and the narrator states that if the roof is painted aluminum that you better know the paint is very well adhered to the aluminum.

 

So if anyone has used this installation and put a bunch of miles on it, that would be  comforting to know. And which sealant was used.

 

AM Solar told me that for an aluminum roof  use the Sikaflex 221 sealant to cover the feet because it contains an adhesive unlike others such as Dicor.

[Zirdu]

I used a similar mounting method as outlined in "Flexible Solar Panel Installation."  I attached my homemade mounts with VHB tape, and then went around the mounts with Sikaflex 221.  The Sikaflex protects the VHB tape, and also adds a bit of adhesive to the mount.  This method bonded  the mount VERY well to the painted aluminum roof, and has remained for over a year now.  It shows no signs of coming off - in fact it would be a major task to remove the mounts from the roof, though very possible with a lot of patience.  

[badtoytrd]

I just installed mine and I would say the hold rivals that of using screws. Taking a trip from VA to SC next week. I’ll report back. Posted some pics here: http://www.wanderthe...ll/#entry195380

Edited by badtoytrd, 02 May 2018 - 11:52 AM.

[JaSAn]

Having worked for 3M for 20+ years and tested a number of their adhesives, I have two comments:

1. The bond is only as good as the strength of what it is attached to.  If the roof paint has a solid attachment to the aluminum (it should), then:

2. Preparation is critical.  Follow the manufacturers instructions EXACTLY.  VHB adhesives do not do well when attached to wax, dirt, road grime, oxidIzed paint, . . .  

 

And obviously, the larger the contact surface the stronger the connection.

 

As to whether the bond is as strong as screws; I've not seen anyone test to failure, so can't say.  A number of installs have used VHB tape with no failures I have seen.  MDOT is gluing together a highway bridge across the St. Croix river in Stillwater, MN.

 

YMMV

 

 

[BillTheHiker]

I just installed mine and I would say the hold rivals that of using screws. Taking a trip from VA to SC next week. I’ll report back. Posted some pics here: http://www.wanderthe...ll/#entry195380

Thanks. Have a great trip and will look forward to your report.

[Sharx]

I posted a reply on VHB awhile back so I will add my knowledge of it again if it helps.  Back in the 80's, I worked for a distributor of 3M and they came out with VHB tape.  Being in Silicon Valley back then, it did not take long for people to start coming up with ideas of how or where to use it.  One of the first things we did to show customers its strength was to attach the 10 mil thick (not double sided foam tape type) double sided "tape" between 2 pieces of 4 inch long aluminum (cleaned and prepped) I-Beam.  In less than 10 seconds, no one could pull it apart and you could get a very good hand grip on each I-beam.  That piece sat on top of our will-call desk for months and we would challenge anyone to attempt to break the adhesive bond.  The most burly guys tried but no one could.  Finally, after many, many tries, the aluminum on one of the I-beams broke.  I will add that we tried the 5 mil thick and it would not hold long at all.  We found that the best use for this new stuff was attaching name or serial number plates to parts or equipment.  The only way you could remove one of these was to use a razor blade or a very nasty solvent.  Water did not seem to faze it at all.

[BillTheHiker]

Pretty amazing stuff.

[kmacafee]

The windows in the tallest building in the world - the Burj Khalifa in Dubai - are all held in place with 3M adhesive similar to VHB. So far as I know, they have not lost any.

[Optimistic Paranoid]

If I were concerned with attaching the tape to painted aluminum, I would cut some pieces of sheet aluminum, say 6"x6" and tape one to the roof at each point the panel foot was going to go.  That way, the panel would be attached to bare aluminum, and the 6"x6" piece of sheet aluminum would have many more square inches of tape holding it to the painted aluminum roof, thus spreading out the forces.

[NRVhawk]

Another trick for improving adhesion to paint is to gently scuff up the paint surface with a mild abrasive pad like scotch-brite, to create circular micro-scratches that help with mechanical interlocking of the adhesive to the point.   Good adhesion results from both chemical bonding and mechanical interlocking.

 

I don't doubt that the VHB tape is up to the job - the data sheet for the 4950 VHB tape that AMSolar sells says that its dynamic tensile strength bonded to aluminum is 140 psi (with good surface prep).  That's pretty impressive!   However, the data sheet also says that painted surfaces (like the acrylic enamel on the FWC roofs) have lower surface energy than aluminum, and can benefit from the use of a primer or adhesion promoter in order to achieve good adhesion.  So, when I get around to mounting a solar panel on my roof, I'll probably use 3M Adhesion Promoter 111 before applying the VHB tape.