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woundedpig
06-29-2017, 10:10 PM
I contacted 3M trying to get some help figuring out how to get appropriate width of VHB to get full coverage of some solar panel mounts I plan to use for some compact 40X20 inch 100W Renogy panels (not flex panels). I want to have the option to remove the panels in the future and feel they have advantages in terms of durability, failure risk, and output at high panel temps. The panel mounts have a base that is almost 4 inches long by 1.34 inches wide.The panels will be 1.2 inches off the roof surface when mounted. Not as stealthy as flex panels but not bad. I'd like to avoid screws, but would consider them - there are already screws up there.

I got the response below. ? Is this a CYA response? Maybe I should have expected it. I don't know which 3M tape # or how much they use to hold trucks together but it is not 4 sq inches per pound of weight supported. AMSolar's site says they use 4950 for mounting panels on Airstreams as well as fiberglass roofed RV's (but not rubber roofs).

Thoughts?

David

__________________________________________________ ____________

Thank you for contacting 3M, where we apply science to life.

I am not sure where you heard the 4950 VHB tape is frequently used for this type of application. We do not suggest that particular VHB, and in fact, VHB can be used for this application, but we suggest it in conjunction with mechanical fasteners. VHB was not intended for this application as a sole means of bonding it due to many factors. The 4950 tape is mostly used for metal to metal applications. We have other VHB tapes that will bond much better to fiberglass. I would suggest to test our VHB tape #5962 along with our adhesion promoter 111. We suggest to use 4 square inches of tape, per pound of weight it will support. I have attached the data page for review. Please read over all the application instructions as surface prep, how much tape to use, set up time, etc. is all listed. You won't need to get an exact width of tape for the width of the panels, as long as you can get the 4 sq. inches per pound around the diameter. Also, use the mechanical fasteners in addition to the tape. This is suggested to support the wind loads it will see going down the highway.

You can find these products on Amazon.com, R S Hughes, or Grainger, usually in smaller rolls or broken cases.

If you need further/additional assistance or prefer to speak directly with a specialist please call 1-800-362-3550 for the first available representative.

autostaretx
06-29-2017, 11:52 PM
Reading the data sheets, the 4950 certainly looks the better way to go.
The only thing 5962 has going for it is a thicker, more conformable layer between the two adhesive surfaces.

The 4950 has a 140 pounds per sq inch straight pull rating, whereas the 5962 is only 90 pounds.
The peel ratings are about the same (25 vs 22 lbs per inch). The overlap shears are the same (80 psi).

4950 family data sheet: http://multimedia.3m.com/mws/media/1267925O/vhb-tape-specialty-tapes.pdf
5962 (5952 family) data sheet: https://multimedia.3m.com/mws/media/67100O/3mtm-vhb-tapes.pdf

... i'd still put bolts and nuts through the leading edge's feet.

Your panels are 5 and a half square feet of (potential) sail... if they start to lift at all at 60 mph, you've got LOTS of relatively little(??:wtf:) force involved.
Cranking through lift and drag calculations for a flat plate (and ignoring the fact the Sprinter is under the panel) shows only 30 pounds of upward force (lift) for a 5 degree angle of attack at 60 mph on your panel. The drag force is only about 18 ounces.

--dick
(there's another thread of someone having his flexible panels peel off, i don't recall the adhesive or tape he used)

HarryN
06-30-2017, 12:28 AM
There is quite a large thermal expansion mismatch between fiberglass and aluminum. In addition, the solar panel mounts will experience quite large thermal cycles each day.

I wonder if their recommendation for a version with a thicker, more compliant version is related to buffering this cyclical thermal expansion effect?

About 15 years ago I was experimenting with mechanically and thermally bonding the LED thermal mount points to a combination electrical / thermal substrate. I tested several adhesives fairly aggressively and two things became very obvious:
- The surface preparation and pre clean effect was greater than the difference between the adhesives I tested.
- The lower spec but more mechanically compliant adhesive performed substantially better than the stronger, more rigid one - in mechanical shock testing.

woundedpig
06-30-2017, 12:43 AM
Yes, I'm working my way through the 3M data sheets - wish I was a materials chemist. There was a person whose flex panel came off who used Sikaflex 221 as his adhesive. He said that this version of Sikaflex is more sealant than adhesive. His flex panels had a polyethylene coating on the rear that was intended to be protective, but was a very poor bonding surface. He ended up using Eternabond tape around the edges.

It seems hard to argue with the success of AM Solar's use of VHB/no screws, and all the installers who are out there full-time RV'ing and installing systems.

David



Reading the data sheets, the 4950 certainly looks the better way to go.
The only thing 5962 has going for it is a thicker, more conformable layer between the two adhesive surfaces.

The 4950 has a 140 pounds per sq inch straight pull rating, whereas the 5962 is only 90 pounds.
The peel ratings are about the same (25 vs 22 lbs per inch). The overlap shears are the same (80 psi).

4950 family data sheet: http://multimedia.3m.com/mws/media/1267925O/vhb-tape-specialty-tapes.pdf
5962 (5952 family) data sheet: https://multimedia.3m.com/mws/media/67100O/3mtm-vhb-tapes.pdf

... i'd still put bolts and nuts through the leading edge's feet.

Your panels are 5 and a half square feet of (potential) sail... if they start to lift at all at 60 mph, you've got LOTS of force involved. (math may appear here in a bit...)

--dick
(there's another thread of someone having his flexible panels peel off, i don't recall the adhesive or tape he used)

rollerbearing
06-30-2017, 01:09 AM
A few of us beat this horse to a very bloody pulp over in the Winnebago Itasca area. Do look up wind uplift forces and what causes them. Also please realize VHB is not some miracle adhesive. It's tensile strength is comparable to silicone. And yes, AM solar seems to have an excellent track record.

autostaretx
06-30-2017, 01:15 AM
Math happened:

... you've got LOTS of relatively little(?:wtf:?) force involved.
Cranking through lift and drag calculations for a flat plate (and ignoring the fact the Sprinter is under the panel) shows only 30 pounds of upward force (lift) for a 5 degree angle of attack at 60 mph on your panel. The drag force is only about 18 ounces.

--dick (quite surprised by the result)
p.s. the Sprinter under the panel increases the lift ... quite like flying in "ground effect"

rollerbearing
06-30-2017, 01:47 AM
Wind up lift forces for buildings - caused by vortexes rolling over the corners creating a low pressure over the flat surface - can be as high as 50 psf at the edges and around 20 psf in the middle of the roof area. These are usually just spot type loads - not uniformly applied over the entire roof area. But, mulitply 50 psf times just 1/4 of your panel area to get an idea of what kind of loading you might see on one footing. Up around 100 pounds!

rollerbearing
06-30-2017, 01:51 AM
Wind uplift on building mounted solar panels:

http://files.engineering.com/getfile.aspx?folder=9ab9a775-c42b-4395-bf1c-8cfda959c70a&file=Wind_Load_blanksstudyreport3.pdf&__hstc=212727627.98870c8ea31a6f7052f610dd61698efe. 1483430608001.1483430608001.1483430608001.1&__hssc=212727627.1.1483430608001&__hsfp=1236935214

autostaretx
06-30-2017, 02:05 AM
It should be noted that my lift/drag calculations were based upon 60 mph driving speed in still air.

If you hit a 60 mph headwind (let's say driving into a rain squall), the force goes up by a factor of four (lift and drag are V-squared beasties)

If your panels are mounted at the front of your roof: look at the slope up from your windshield... that's going to be vectoring the wind to a greater angle of attack.

--dick
p.s. i notice that that solar panel wind load report specifically mentioned that they (also) did NOT take into account the close-to-subsurface "ground effect" contribution

rollerbearing
06-30-2017, 02:42 AM
VHB also tends to creep when constantly loaded - that is why they recommend 4 sq. inches per pound for constant loads. It does much better under intermittent load/unload situations where it does not creep. But even then it does experience some small level of cycle fatigue. Don't get me wrong, the stuff works for many people - just be sure to have PLENTY of safety margin and possibly consider mechanical fastener back up (AM Solar does reccomend screws - at least in some places on their web site)

woundedpig
06-30-2017, 03:53 AM
I still don't get the 4 sq. inches per pound or load spec. It seems incredibly conservative. When I first heard about VHB, I went online and especially looked at youtube videos of industrial applications and demonstrations of sheer strength etc. These demos used nothing approaching the above spec of 4 sq in/lb load. VHB tapes are used in aircraft flying at tremendous speeds experiencing huge forces and heavy trucks bouncing down the road. I just looked at the aircraft and automotive applications sections on the 3M site.

rollerbearing
06-30-2017, 04:12 AM
It has to do with that slow creep problem for constant static loads. Especially in shear. Things like picture frames. It is still a problem in static tension as well. You could hang a big old light fixture over your dinning room table and find it crashed to the floor the next morning.

Dynamic tension loading is a different matter - so much stonger! This is the kind of loading you are seeing on the truck trailer sidewall panels - if it doesn't have to hold the panel's weight up - ie the bottom edge of the truck sidewall is resting on a frame. In this case you'll see VERY much lower reccomendations.

They can't expect the general public to always know the difference so they are quoting you the shear static load number. That would apply if you wanted to stick panels on the side of your RV (without anything else supporting their weight.) Having them sit flat on the roof supported from below they are mostly going to experience tension loading some of which will be dynamic - from vortexes and some may be constant from angle of attack uplift as Autostartex calculated.

ablock
06-30-2017, 04:56 AM
What about adding a strip of Eternabond over the mounting foot, with say 1.5" of overlap on all sides?

I don't see what #8 screws into a FRP skin panel is going to do for you. I assume the roof core has essentially zero resistance to pullout.

Aqua Puttana
06-30-2017, 07:12 AM
...

I don't see what #8 screws into a FRP skin panel is going to do for you. I assume the roof core has essentially zero resistance to pullout.
Some ss screws might do more than you might think.

Is the roof plastic or composite - fiberglass? If composite the fasteners should lock in quite well. If plastic, not quite as well.

My thought is that the fasteners will clamp the parts together and help prevent the VHB or sealant from losing the bond.

I'm no expert.

I do like the idea of the Eternabond tape for weather seal. I doubt it will add much bonding strength.

I've mentioned before that Plexus adhesive has been used to bond boat decks to the hulls for quite some now. It is very effective.
http://www.itwplexus.com/UserFiles/File/Guide_To_Bonding.pdf


:2cents: vic

rollerbearing
06-30-2017, 01:32 PM
What about adding a strip of Eternabond over the mounting foot, with say 1.5" of overlap on all sides?

I don't see what #8 screws into a FRP skin panel is going to do for you. I assume the roof core has essentially zero resistance to pullout.

A bit better than screws are through bolts backed with load spreading plates. My fasteners on the interior are hidden in cupboards and behind ceiling AC vents. They are covered on the exterior with self leveling sealant. Agree with Vic about marine adhesives. Look up tensile strength of 3M 5200 and compare to VHB. Look up tensile strength of hardware store Permatex Silicone and compare to VHB.

Nonetheless, MANY people have used just VHB. If you go that route - really understand what you are doing - have plenty of safety margin (like 5X) and consider backing up with mechanical fasteners. The closest engineering data you will find is from the building trade - look up roof decking screw fastening schedules and wind uplift values. VHB is cheap and this is a case of a little seems to work and more is probably better (and sure wouldn't hurt anything or anybody.)

ablock
06-30-2017, 03:08 PM
A bit better than screws are through bolts backed with load spreading plates.

I would say that would be much better, as in, that would be the marine industry standard. But also impossible in the Unity as the interior roof panels cannot be removed AFAIK.

5200 would be a good choic if you never, ever expect to need to remove the solar mounts.

woundedpig
06-30-2017, 03:28 PM
This is AMSolar's view: On fiberglass roofs they use VHB without screws with mounts that have just 2.5 sq inches of base area each. The Renogy mounts have twice that surface area each. 80 pounds of shear force per square inch of VHB = 800 pound of shear force using the AMSolar mounts, and twice that using the Renogy Z brackets. I tend to over analyze things and I'm in that phase right now.......... Still pondering. I don't know how thick the fiberglass shell is for the Leisure Travel Unity and don't know exactly what is underneath (4 inches thick) but wonder what the resistance to screw pullout really is, like Ablock.

I just heard from Garret, an engineer at AMS. He said that 3M's response looks like a "CYA" to him and again, no failures. He suggested adding an extra mounts when the panel is mounted near the leading edge of a vehicle where there might be laminar airflow and said that AMS tends to add extra L-Feet to increase the contact area in such a setting.

autostaretx
06-30-2017, 04:33 PM
There are so many issues at play here... if you simply #8 or #10 sheet-metal-screw it to the fiberglas, i'd really be worrying about pull-out (if the VHB failed/crept). But you'd certainly be helping in the straight-to-the-rear shear issues.

Next up would be to drill a bigger hole, and insert/install a Molly-like T- or expansion "nut" ... there's a WingIts brand for ADA handrails which uses two coupled broad-spreading plastic tripod back supports ... good enough to exceed 600 pound support in 5/8" wall board, so quite likely decent for fighting lift effects of a panel.

A problem with putting any hole in the fiberglas is the potential for fatigue/stress cracks spreading from it as the roof flexes up and down from the winds buffeting the panel. Bigger, smoother holes help minimize that.

Me? I'd accept the minor cosmetic damage of cutting through the ceiling inside the van to reach one or two of the forward feet to provide a load plate (my reason for saying "bolts and nuts" earlier... i'd certainly include load-spreading fender washers (at least)). You can always hide the ceiling hole with a new LED light fixture or the like.

--dick
p.s. when i installed my MaxxFan, i went the route of installing a wooden frame beneath my steel roof to receive its mounting screws, instead of just trusting the 12 or 16 screws' threads in the sheet metal alone. Belts and suspenders.

chromisdesigns
06-30-2017, 04:37 PM
Based on boat experience I would make wooden or aluminum mounting pads, glue them down with 3M 5200 polyurethane and screw or bolt the panels to the pads.

Using 5200 you can probably lift the van by the pads! That stuff sticks.

And if you ever have to remove them for some reason you can cut them off with a length of thin wire fishing leader

Bone Head
06-30-2017, 05:37 PM
Math vs. REAL WORLD:

My Renology solar panels are attached with VHB tape (don't know which number) for a couple of years now and have been from Wisconsin to Texas to California and Alaska without as much as a whimper. I do go up on the roof every once and a while to check, but for my money, no penetrations is a good thing.
I understand the math and the concern, but let's face it folks, the VHB tape just works.

Bob

Klipstr
06-30-2017, 05:57 PM
Math vs. REAL WORLD:

My Renology solar panels are attached with VHB tape (don't know which number) for a couple of years now and have been from Wisconsin to Texas to California and Alaska without as much as a whimper. I do go up on the roof every once and a while to check, but for my money, no penetrations is a good thing.
I understand the math and the concern, but let's face it folks, the VHB tape just works.

Bob

Just what we needed: a real life guy interfering with the theory guys. Dang.

I sika'd mine to roof. 9K miles and nothing moving so far. Flex panels so no leading edge issues, all the uplift stuff. Further back on the rig as well.

woundedpig
06-30-2017, 06:06 PM
Math vs. REAL WORLD:

My Renology solar panels are attached with VHB tape (don't know which number) for a couple of years now and have been from Wisconsin to Texas to California and Alaska without as much as a whimper. I do go up on the roof every once and a while to check, but for my money, no penetrations is a good thing.
I understand the math and the concern, but let's face it folks, the VHB tape just works.

Bob



Bob, did you use these broader based Renogy mounts?

https://www.amazon.com/Renogy-Solar-Panel.../dp/B00BR3KFKE


and did you do a full after-market install (not LTV) ? Are these rigid panels - if so, why did you choose them over flex? If they are rigid, how stealthy was the end result appearance?


Thanks

David

rollerbearing
06-30-2017, 06:37 PM
Math vs. REAL WORLD:

I understand the math and the concern, but let's face it folks, the VHB tape just works.

Bob



Until it doesn't. Sometimes the REAL WORLD is cruel. There are other examples. Note this was a VHB to paint bond. Still, the caution is know what you are doing.

Look at the 6th post by marco polo:

http://www.classbforum.com/forums/f23/solar-panel-on-roof-1787.html#post8728

woundedpig
06-30-2017, 08:49 PM
Until it doesn't. Sometimes the REAL WORLD is cruel. There are other examples. Note this was a VHB to paint bond. Still, the caution is know what you are doing.

Look at the 6th post by marco polo:

http://www.classbforum.com/forums/f23/solar-panel-on-roof-1787.html#post8728

Well that's the thing - details - I tried to get into that forum to read the details of the VHB failure in a 190 Roadtrek (it looked like) but it was a closed Yahoo group for Roadtrekers. Lot of factors there - the paint and its condition, whether the roof was curved, ribbed at all and the mounts were flat, prep method, whether the mounts were covered with Sikaflex or Decor and inspected at intervals, etc.
There are some mounts out there with only about 1 - 1.5 inch base dimensions - less grab surface.
I know the Unity roof is fiberglass, but is it painted, like the sides/rest of the vehicle? Fresh cured/baked paint should form a good bond.
I will probably take a caution course with extra mounts, but not sure I want to use screws. I just don't know about the holding power. I also don't know what the layers in the roof are - think there is a thin wood layer under the fiberglass, but can't confirm.

rollerbearing
06-30-2017, 09:11 PM
Details - exactly! And don't under estimate the forces it might see (or may never see). Keep in mind for aerospace applications they actually test samples under all kinds of conditions until failure. We can't do that with our RVs. For example, how strong is my gelcoat? I don't know unless I rip some off. However, I can look up a "number" and get an idea of what it MIGHT be in general. Just be thoughtful and add some extra for those things that none of us noticed or thought of.

It struck me as funny that this winds up as two camps butting heads over chemicals. One camp sees VHB as its marvel (no holes) and the other camp sees lap sealant as its marvel (no leaking holes). We all have holes in our RV roofs protected by some sealant or another.

alichty
06-30-2017, 11:41 PM
......
I know the Unity roof is fiberglass, but is it painted, like the sides/rest of the vehicle? Fresh cured/baked paint should form a good bond.
I will probably take a caution course with extra mounts, but not sure I want to use screws. I just don't know about the holding power. I also don't know what the layers in the roof are - think there is a thin wood layer under the fiberglass, but can't confirm.

The roof has a rougher surface than the sides of the coach but it does appear to still have automotive paint and clear coats on it.

Aqua Puttana
07-01-2017, 02:28 AM
Given my very basic loft bed iron tent Sprinters I don't have a dog in this race.

... We all have holes in our RV roofs protected by some sealant or another.
Sealants/adhesives have improved so much over the years that I don't worry very much about penetrations in the roof of vehicles or RV's... including boats.

For both my 2004 and 2006 roof vent installations I beat a roof rib into submission and then completely depended upon the sealant/adhesive to hold the water out. So far that has worked for me. (The 2004 did have a bit of leaking, but it was not where I beat the rib into shape. The failure was in the plastic flange vent mount unit. My 2006 vent has a metal flange.)

Some comments assume that any mechanical fasteners are going to see pullout stress. In most all cases the fasteners will probably see more shear stress than pullout. Combining VHB tape or adhesive sealants with mechanical fasteners will be very strong. Eg - 3M recommended adding mechanical fasteners. CYA or not, it is a belt and suspenders approach that will give good results.

Personally I would just add a few mechanical fasteners and seal them properly.

:2cents: vic

Incredulocious
07-01-2017, 04:04 PM
Just what we needed: a real life guy interfering with the theory guys. Dang.

I sika'd mine to roof. 9K miles and nothing moving so far. Flex panels so no leading edge issues, all the uplift stuff. Further back on the rig as well.

Here's the details on my failed experience with Sikaflex with flexible panels, as well as my exploring alternatives:
http://crimdom.net/rv-upgrades-and-customizations/#panel-adhesive

Boxster1971
07-02-2017, 02:10 AM
AM Solar recommends covering the mounting with sealant when using VHB tape.

http://amsolar.com/diy-rv-solar-instructions/edmounts/

They have used the tape since the 1990's and have never lost a panel.

Aqua Puttana
07-02-2017, 12:54 PM
AM Solar recommends covering the mounting with sealant when using VHB tape.

http://amsolar.com/diy-rv-solar-instructions/edmounts/

They have used the tape since the 1990's and have never lost a panel.
They seem to contradict themselves. :idunno:

Roof Attachment

Fiberglass roofs – We have been using a type of 3M double-sided tape on our mounts since the mid 1990’s, and we have never lost a panel. As long as the tape is properly installed on a clean surface at the correct temperature, it will hold. As an added level of protection, we use a layer of Dicor self-leveling sealant around the entire perimeter of the mount, and cover the screw holes/heads as well. The sealant protects the tape and any potential roof penetrations from water intrusion and decay.

Rubber Roofs – Along with the 3M double-sided tape, we also include stainless steel ” sheet metal screws in the Rocker Foot Mount Set. While the 3M tape will hold to your rubber roof, your rubber roof may not stay attached to the plywood it is bonded to. The sheet metal screws will penetrate through the rubber, into the plywood, to keep your rubber roof from separating while the wind force of highway speed driving pulls at your panels. Again, we bury the entire mounting feet with Dicor self-leveling sealant for weather resistance. Some customers use the screws for an added layer of protection on fiberglass roofs, but we haven’t found that to be necessary.

They don't say not to use screws as is recommended in writing by 3M.

I see no downside with a couple ss screws completely covered by Dicor sealant. It won't leak.

:2cents: vic

Added:
I forgot to include that in the mounting smaller picture it appears the Dicor sealant covers a screw head.

rollerbearing
07-02-2017, 04:14 PM
Another set of postings where it is not clear if AM solar is recommending screws or not. Things are not consistent. Which kind of points out that one size does not fit all in this situation. VHB works - just be sure you know what you are doing.

http://www.classbforum.com/forums/f23/attaching-solar-panel-s-coachmen-class-b-5593.html

scroll down to Marcopolo

Also, it is worth watching the foot removal video mentioned in the above thread. Note isopropyl may have little to do with the removal - it may only be preventing it from re-sticking. 3M's literature states that VHB is fairly resistant to isopropyl. Notice how quickly the whole thing lets loose with no warning. Levering the mount over like he is doing puts the tape into a combination of "peel" and tension. I'm not saying VHB is too weak if properly applied, but it is clear that it can fail suddenly and completely with out warning when it reaches it's limit. Periodic "checking" may not show anything. Just be sure you use enough that you don't reach it's limit.

Bone Head
07-02-2017, 04:49 PM
Bob, did you use these broader based Renogy mounts?

https://www.amazon.com/Renogy-Solar-Panel.../dp/B00BR3KFKE


and did you do a full after-market install (not LTV) ? Are these rigid panels - if so, why did you choose them over flex? If they are rigid, how stealthy was the end result appearance?


Thanks

David

David,
I used the "standard" 1" X 4" Renology mounts with VHB the same size as the base. I mounted the panels fore and aft with NO additional fastners. I merely cleaned the roof surface with soap and water and then Denatured Alcohol (once again, what I had on hand). I then applied the VHB to the cleaned and scuffed up mounting feet and stuck them down to the prepared roof surface. I used cable tie type surface mount wire holders every foot or so and tied the two new panels into the factory 95 watt panel wiring in parallel.
I have nothing against using screws and Dicor or similar, but after my limited research I decided that this was adequate to satisfy my needs.

The panels are rigid and I have come to appreciate the benefit of air space under the panel to aid cooling. As far as I know, the watt/dollar ratio still favors the rigid PV panels, but I haven't done any looking recently.

As to stealth, there is nothing stealthy about a fancy LTV motorhome with antenna, A/C and other roof penetrations so I don't worry about it.

Please note, that I am not an expert on solar, but I do have an additional 33 PV panels on a post mount system for my house so would not consider myself to be a solar virgin either. I also have a single Renology panel which was destroyed in shipping operating through a PWM controller to maintain the batteries in my LTV while it is stored inside my pole building. The damaged panel does not put out anything near it's rated wattage but it does keep the coach and chassis batteries topped off through the Trik-L-start.

rollerbearing:
I could have used logging chains and cables to hold them down, but that seemed to be overkill.
Catty? Me? NEVER.
That said, I see no reason why I would try to convince anyone not to install in a way which makes them feel that they have done their due diligence and satisfied their standards.

Bob

rollerbearing
07-02-2017, 04:58 PM
Bonehead,

Catty? Meow.:bounce:

Just trying to make clear that people need to understand their situation. Some have paint, some have fiberglass, some have flex panels backed with plastic that peels away, some roofs are curved, and on and on. It's not a case of here are four feet and some tape - you're good to go. Or is it?

Bone Head
07-02-2017, 05:13 PM
Bonehead,

Catty? Meow.:bounce:

Just trying to make clear that people need to understand their situation. Some have paint, some have fiberglass, some have flex panels backed with plastic that peels away, some roofs are curved, and on and on. It's not a case of here are four feet and some tape - you're good to go. Or is it?

Totally agree. We are on the same sheet of music.
Glad you took that in the spirit in which it was intended.

Bob

Aqua Puttana
07-02-2017, 06:27 PM
... It's not a case of here are four feet and some tape - you're good to go. Or is it?
Sure it is. As long as you don't own the rig or have responsibility for the installation. :bounce:

I believe the discussion helps. Not one member is under obligation to take any of the advice.

(I almost wrote not one SS member... then I realized the political implications. :hmmm: German Sprinter van... Sprinter-source name selection... conspiracy theories could go viral.)

Back to topic though.

vic

Klipstr
07-03-2017, 09:10 PM
Well that's the thing - details - I tried to get into that forum to read the details of the VHB failure in a 190 Roadtrek (it looked like) but it was a closed Yahoo group for Roadtrekers. Lot of factors there - the paint and its condition, whether the roof was curved, ribbed at all and the mounts were flat, prep method, whether the mounts were covered with Sikaflex or Decor and inspected at intervals, etc.
There are some mounts out there with only about 1 - 1.5 inch base dimensions - less grab surface.
I know the Unity roof is fiberglass, but is it painted, like the sides/rest of the vehicle? Fresh cured/baked paint should form a good bond.
I will probably take a caution course with extra mounts, but not sure I want to use screws. I just don't know about the holding power. I also don't know what the layers in the roof are - think there is a thin wood layer under the fiberglass, but can't confirm.

If I were to put rigid panels up on mine I would want to put at least one screw per mount and if in that much then why not two or three depending on the mount? The roof is a thin fiberglass backed by either 1/4 or 3/8 ply and then some Styrofoam and insulation. I know this from pulling the original solar penetration off. As for putting a screw into that: I've done it on my previous three rigs. Drill a narrow pilot hole, smear the bottom of the mounting bracket with non leveling dicor, place and put a 3/4" #10 sheet metal screw in. Then dicor the top of the screws. The dicor basically acts as a glue between the mounting bracket and roof and screw holds the whole mess down until the glue dries. One could use epoxy or gorilla glue between the bracket and roof and then dicor which might be even better. I do like the idea of a chemical as well as mechanical connection between panel and roof.

I used this method on three previous installs and recommended it to many many others as has Handy Bob. I've never had one fail and have not heard of any. But...

Angle of attach on the leading edge of the panels would be my main concern. If one could angle the leading edge downward a bit that might help with the most obvious wind load lifting the panel off the roof. Can't speak to the wing effect as my engineering degree is in electrical and mostly computers at that so very little practical useful information there!

Unfortunately one will never know until one reaches the failure point!

woundedpig
07-07-2017, 08:09 PM
Since I've never been to the factory or seen pictures of the roof cutouts before, I asked Don K about the layers of the roof. I told him my reason was for consideration of using screws for rigid solar panel mounts. His response below and picture attached. If I'm seeing this right (left side of the pic) the fiberglass layer seems thicker that an inner, very thin wood panel, then styrofoam? Not sure that Don's thicknesses jive with what I see.
Still not a lot of thickness overall. If I were to use VHB **and** some judicious screws, say one in each mount, but more in any front, windward leading edge of the panel, I wonder if this would be the chemical plus mechanical compromise I need.
Also, which screws? Most mount kits have longer self tapping screws that don't seem optimal and are too long. Seems like 3/4 or 7/8 inch at most pan head stainless steel machine screws would be good, using careful pilot holes. Wood screws with coarser threads wouldn't have many bites in the outer roof layers.
?? Thoughts
__________________________________________________ __________________________-
...............I included a picture of a roof after it has gone through the Sandwich Dept. where it is all laminated together. Here you can see the 1/8 Fiberglass and then the 1/8 wood paneling. And the 5 of Styrofoam insulation in the center and it narrows to 3 on the sides. In-between all of this is an Aluminum frame work in the roof.
__________________________________________________ __________________________

Thanks
David

HarryN
07-08-2017, 12:40 AM
That is a very helpful roof cut away photo. I wonder if it is possible to find the aluminum frame work with a stud finder?

woundedpig
07-08-2017, 12:52 AM
Someone on the forum demonstrated that the aluminum rib location can be visualized on a dewey morning where the heat transmittance makes the rib locations visible. Unfortunately the ribs may not line up well for placement of multiple panels.

triguy2001
07-08-2017, 05:35 AM
Used the am solar mounting kits with (4) sp100's in St. Louis in the winter with a heat gun to heat the area the feet would stick. Fast forward to cleaning and checking them today, they aren't going anywhere... the tape works..

calbiker
08-25-2017, 12:49 AM
Just what we needed: a real life guy interfering with the theory guys. Dang.



Chiming in a bit late, but another real world data point. Almost 11 years, 90K miles, VHB bond is still rock solid on a Winnebago fiberglass roof. My panel tilts and seen some strong winds in the tilt position.

Each pad has 24 sq in of surface area.

Graphite Dave
08-25-2017, 01:07 AM
Bottom line is I like the four 5/16" SS bolts that anchor my single 300 watt panel through the roof. Unfortunately I have little knowledge of adhesives so have to resort to what I know.

woundedpig
08-25-2017, 03:18 AM
Chiming in a bit late, but another real world data point. Almost 11 years, 90K miles, VHB bond is still rock solid on a Winnebago fiberglass roof. My panel tilts and seen some strong winds in the tilt position.

Each pad has 24 sq in of surface area.

You've seen some pretty rough off-roading, too!

David

woundedpig
08-25-2017, 03:58 AM
I've been posting on the FB Leisure Travel Vans Enthusiasts forum and received a picture of a small section of the outermost layer of the roof of the Unity, whose outer layer is called Vetrolite or Flexroof. It looks a good bit thicker than the previous picture I posted earlier in this thread, which is most likely the wall cross section, which has a thinner outer layer. The first picture was sent to me by Don Klassen, but it looks to be the sandwich structure of the wall, not the roof. So it looks like there is a **little** more substrate in which to sink screws, if some screws plus VHB all around was the method chosen to secure the panels to the fiberglass roof. Still, looking at that roof structure, I really wouldn't be comfortable with just screws plus Dicor, Sikaflex or some other lesser adhesive than VHB.

vantastic adventure
08-28-2017, 09:06 PM
Chiming in a bit late, but another real world data point. Almost 11 years, 90K miles, VHB bond is still rock solid on a Winnebago fiberglass roof. My panel tilts and seen some strong winds in the tilt position.

Each pad has 24 sq in of surface area. Nice mounts and system! Do you happen to have a thread or more pictures of how the supports work?

msmolow
11-17-2018, 02:39 PM
I'm resurrecting this thread. One year later, does anyone have further experience with using VHB without hardware?

Mitch

Klipstr
11-17-2018, 03:46 PM
I'm good through 14000 miles, most smooth some VERY rough. 9 square inches per pad, four pads per panel. Rock solid.

msmolow
11-17-2018, 04:08 PM
Custom made pad or stock?
I'm considering Renogy curved Z
https://www.renogy.com/renogy-solar-panel-mounting-curved-z-bracket-set-of-4/

TManSTL
11-17-2018, 05:30 PM
Custom made pad or stock?
I'm considering Renogy curved Z
https://www.renogy.com/renogy-solar-panel-mounting-curved-z-bracket-set-of-4/

msmolow, I've had my panels on for 6 months and they are still rock solid with a VHB-only install.

Prior to my install, I went back and forth trying to decide if I really wanted to put 48 more holes in my roof or risk using only VHB. Going the "48 screw hole" route meant the possibility of a future leak and more maintenance on the Dicor seals. On the other hand, picking the VHB-only install meant that I had to risk losing one or more panels in high winds while driving down the highway.

I ultimately decided on the VHB-only approach. However, I wasn't comfortable with the mounting brackets that are readily available from many suppliers due to the lack of bracket adhesion area. So, I decided to make my own brackets out of aluminum T-bar from OnlineMetals.com. (https://www.onlinemetals.com/merchant.cfm?pid=21875&step=4&showunits=inches&id=929&top_cat=60)

I created 24 pieces of the 2"x2" T-bar in 6" lengths. Each bracket gives an adhesion area of 12 square inches per bracket for a total of 48 square inches of adhesion area per panel. Although I drilled screw holes in each bracket, I did not end up using them and opted for VHB only. Before applying the VHB, each bracket was cleaned thoroughly with isopropyl alcohol. It is very important that the surface preparation is done properly to both the bracket and roof before applying the VHB and adhering the bracket to the roof.

As a precaution, I went ahead and applied Dicor self-leveling compound around the base of the brackets after adhering to the roof to prevent water from seeping in to the VHB seal and possibly affecting the adhesion. This step was probably not necessary, but I wanted to err on the side of safety.

After recently checking the panels for proper adhesion, I gotta tell you that it will take a jackhammer to get these things off! I'm very happy with the results and give 3M a big thumbs up for creating VHB...what an amazing tape!

Aqua Puttana
11-17-2018, 05:58 PM
...

As a precaution, I went ahead and applied Dicor self-leveling compound around the base of the brackets after adhering to the roof to prevent water from seeping in to the VHB seal and possibly affecting the adhesion. This step was probably not necessary, but I wanted to err on the side of safety.

...
:thumbup:

It may not be necessary, but for anyone taking the vehicle where there is freeze/thaw cycles, I think it is a good addition. I'd also be concerned that over time the water might creep in and affect the bond. The Dicor should prevent the water from being a problem at all. Not to mention that the Dicor must add some adhesive strength to the brackets.

The install looks very good by the way.

:cheers: vic:cheers:

msmolow
11-18-2018, 02:15 AM
That great info. Thanks to all.

TMan, which tape did you use and did you custom make the aluminum end piece on each panel?
Thanks

Mitch

tinman
11-18-2018, 02:38 AM
msmolow, I've had my panels on for 6 months and they are still rock solid with a VHB-only install.

Prior to my install, I went back and forth trying to decide if I really wanted to put 48 more holes in my roof or risk using only VHB. Going the "48 screw hole" route meant the possibility of a future leak and more maintenance on the Dicor seals. On the other hand, picking the VHB-only install meant that I had to risk losing one or more panels in high winds while driving down the highway.

I ultimately decided on the VHB-only approach. However, I wasn't comfortable with the mounting brackets that are readily available from many suppliers due to the lack of bracket adhesion area. So, I decided to make my own brackets out of aluminum T-bar from OnlineMetals.com. (https://www.onlinemetals.com/merchant.cfm?pid=21875&step=4&showunits=inches&id=929&top_cat=60)

I created 24 pieces of the 2"x2" T-bar in 6" lengths. Each bracket gives an adhesion area of 12 square inches per bracket for a total of 48 square inches of adhesion area per panel. Although I drilled screw holes in each bracket, I did not end up using them and opted for VHB only. Before applying the VHB, each bracket was cleaned thoroughly with isopropyl alcohol. It is very important that the surface preparation is done properly to both the bracket and roof before applying the VHB and adhering the bracket to the roof.

As a precaution, I went ahead and applied Dicor self-leveling compound around the base of the brackets after adhering to the roof to prevent water from seeping in to the VHB seal and possibly affecting the adhesion. This step was probably not necessary, but I wanted to err on the side of safety.

After recently checking the panels for proper adhesion, I gotta tell you that it will take a jackhammer to get these things off! I'm very happy with the results and give 3M a big thumbs up for creating VHB...what an amazing tape!

Another data point. My single panel is installed in a similar manner, including length of bonding surface. Four years, travel includes about 1500 miles of gravel roads. Still rock solid. I do park it out of the freeze-thaw in the winter.

SSTraveler
11-18-2018, 11:38 AM
I picked VHB 5952 for its high temp performance, high tensile and shear strengths. I bought 8x12" sheets on Ebay, https://www.ebay.com/itm/3M-5952-BLACK-VHB-045-DOUBLE-STICK-FOAM-TAPE-3-8-X-12-SHEETS-GOPRO-MOUNT/113318280195?hash=item1a624bbc03:g:J6MAAOSwTuJYqlt 3&redirect=mobile and cut the pieces to fit my hand made Aluminum mounting plates (see this thread, https://sprinter-source.com/forum/showthread.php?t=67873&highlight=Solar+install). While I did cover my plates with Eternabond for redundant adhesion I do believe the VHB alone was very adherring and impressive in its bond to the roof. If I were to add more panels I would still go with redundant adhesion methods just because that's what makes me feel comfortable. Also I would use the Renogy Tilt mount brackets, https://www.renogy.com/renogy-rv-tilt-mount-brackets/. I would use the VHB tape to stick them to the roof, should be very strong since there is a lot more surface area, and then cover with eternabond tape for extra strength insurance. I like the idea of these tilting brackets because they do have a lot of roof adhesion surface area (so no need to drill more holes) and you can tilt them up to clean underneath the panels (especially during pollen season) or remove leaves and pine needles (excessive where I live). Also you can angle the panel to get more sun during the winter. It seems the tilt mounts make for an easy install, no new holes, and give you more flexibility to use and maintain your panels and roof.

Wildebus
11-18-2018, 11:53 AM
well, I used VHB Tape to fix my rails down on my T1N but I could not bring myself to not use mechanical fastenings as well.
The potential outcome of something ripping off and flying down the road and causing goodness knows what potential carnage being reduced by the simple addition of a few through-bolts and spreader plates was worth drilling a few extra holes in the roof for.

Tape or Adhesive can only ever be as good as the surface it is attached to and from what I understand about Sprinter Paint quality, it doesn't stick too well? (maybe the Fibreglass shelled vans are better in that respect?

SSTraveler
11-18-2018, 12:02 PM
The tops of our roofs are unpainted gelcoat I believe. I just used windex and Mr. Clean Eraser pad to get the surface really clean and then I wiped the area with Alcohol and stuck down my mounting plates. 3M makes an adhesive promoter that you wipe the area down with that you could use as well, https://www.amazon.com/s/?ie=UTF8&keywords=3m+adhesion+promoter&tag=googhydr-20&index=aps&hvadid=241892317824&hvpos=1t1&hvnetw=g&hvrand=8877182753681261048&hvpone=&hvptwo=&hvqmt=e&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=1025496&hvtargid=kwd-4737511118&ref=pd_sl_11r90huyfr_e. I've used it on other projects and I'm not sure that it really adds anything more that good surface cleaning and alcohol, but some swear by it.

woundedpig
11-18-2018, 01:18 PM
After getting the butt covering response from 3M initially about using VHB tape in this application, I used VHB tape strips just larger in size than the feet of the Renogy mounts, similar to what AM Solar does, but I placed one screw in each mount and covered the mount with Dicor. Around the edge of the roof is an Aluminum band, so half the screws are into metal. I have no angst about putting tiny extra holes in the roof, given the availability of space age sealants. The holes are covered with the mount, the VHB, and the Decor. Also, why have angst about a few extra holes, when we already have several square feet of gaping holes and a several penetrations in the roof? We obviously need to get up there at least once a year and inspect every single inch of caulking and reinforce/replace if needed. Panels are obviously solid as a rock.

Klipstr
11-18-2018, 03:39 PM
Custom made pad or stock?
I'm considering Renogy curved Z
https://www.renogy.com/renogy-solar-panel-mounting-curved-z-bracket-set-of-4/

Custom made. I used the Renogy and then mounted them to 3/8x4.5x2 aluminum with stainless steel hardware. If you search for my solar install you will see a photo. I built another set that I didn't use that had 3/8x6x2. If I did it again I would probably use the larger size just to give a bit more surface area. I don't recall what type of VHB I used but I do know I did research at the time that led me to it.

And what the woundedpig said too! Especially on the outer brackets that will screw right into the aluminum roof frame. Even if the bracket opposite were to suddenly lose all it's adhesion and strength, the rest of the works probably wouldn't allow it to bend upward. And the only way the panel would start to heal upward would be if two of the brackets failed. Especially since the wind load would be from the front rather than the side and one bracket is screwed into metal. And by the time all that happened you would have heard something going terribly wrong above your head! Unless you had your Samsung virtual reality headgear on...

msmolow
11-18-2018, 04:56 PM
Found the pics. Thanks.

TManSTL
11-19-2018, 03:02 PM
That great info. Thanks to all.

TMan, which tape did you use and did you custom make the aluminum end piece on each panel?
Thanks

Mitch

Hi msmolow, I used this VHB tape: https://www.amazon.com/gp/product/B007Y7GJ8O/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

As for the aluminum end piece that is mounted to the solar panel, I used these: https://www.amazon.com/gp/product/B00SBCKLYO/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I could have used the base mounting bracket that came with this kit but since the roof is curved a bit, I made my own base aluminum brackets.

msmolow
11-19-2018, 04:10 PM
Thanks!

Peter Tourin
11-22-2018, 12:02 PM
I just read through this thread for the first time - very interesting, as I've been considering rigid panels for some time. In the discussion about screws/bolts, I'm surprised that there was no discussion of Well Nuts. I think the panel failure thread mentioned them. I know them from another application. Basic idea: you drill a larger hole and insert a flanged cylindrical rubber fitting that has a threaded metal interior bonded to it. When you tighten the bolt, the rubber is forced to contract and therefore swells - that pushes it outwards against the drilled hole. It also swells more on the inside where it's not restricted by the drilled hole, so it provides some pull-out resistance. Rubber, so there's some small amount of vibration cushioning. I'm curious if anybody has thought about these. I'm just a seat-of-the-pants engineer, but it seems like a good application for Well Nuts, especially in the shear resistance department...

TStiles
11-22-2018, 12:14 PM
And for those who would like to see a demonstration of the well nuts that Peter speals of....
https://www.youtube.com/watch?v=WpATnkmKzYI

liquidrock
12-05-2018, 06:15 PM
This, in my opinion, is a CYA answer, as well as sound advice. As much as I would love to tape something to the top of my van and forget about it, NO tape is rated to hold anything to a metal surface permanently.

Bone Head
12-05-2018, 08:02 PM
This, in my opinion, is a CYA answer, as well as sound advice. As much as I would love to tape something to the top of my van and forget about it, NO tape is rated to hold anything to a metal surface permanently.

Seriously? Many trailers are being fabricated with tape rather than rivits holding the sheet metal panels together.

Additionally, the Unity by LTV does not have a metal roof.

Bob