Blind (pop) rivets or rivet nuts (rivnuts) in fiberglass?

[Hawkeye Ed]

Does anyone have any experience using blind (pop) rivets or rivet nuts (rivnuts) for an installation on exterior camper fiberglass?

I'm installing solar panel mounting feet on my 5.0's roof with 3M VHB tape but I'd feel more comfortable adding a mechanical fastener into the fiberglass. I'd rather not drill all the way through the interior headliner to install an interior washer and nut. So I'm thinking I might be able to install a blind rivet or a rivet nut through the fiberglass from the outside without needing to have anything showing on the interior headliner.

Any experience or ideas?

Thanks

Ed

[HABBERDABBER]

Check the McMaster-Carr online catalog for access to a wide variety of pop rivets. You can dial in the type, material and style of pop rivet to use in length and with their selection.

A buddy has used the rivet nuts multiple times, mounting Yakima type crossbars on various vehicles in inaccessible locations. I believe they work well, too.

[occer]

Can the anchor points for the solar panels be located where the wood is located inside the trailer. Maybe one of the sonar stub finders to locate the wood from the outside. Here is a picture of the inside of one of the escape trailers. It is not a 5.0 but I would think it’s similar in all of the trailers.

[Centex]

Originally Posted by Hawkeye Ed

Does anyone have any experience using blind (pop) rivets or rivet nuts (rivnuts) ....

I have the tools and experience using both through appropriate materials; I would not use either for a blind structural fastening into a fiberglass shell.

Reason - neither provides adequate bearing-surface when installed blind without an interior washer / bearing plate; IMO the edge of a hole drilled in fiberglass lacks the integrity to hold-up over long term stress and vibration.

My suggestion is to plan your panel footings at a width such that they fall within the OH cabinets where you can install a proper load-spreading washer or bearing plate for a through-bolt with nut that's not visible in the trailer's living space.

If your panels aren't wide enough for that span, install crossbars which are and fasten the panels to those.

Just one person's opinion for your consideration, Good Luck and Have Fun!

[Ron in BC]

Originally Posted by Centex

I have the tools and experience using both through appropriate materials; I would not use either for a blind structural fastening into a fiberglass shell.

Reason - neither provides adequate bearing-surface when installed blind without an interior washer / bearing plate; IMO the edge of a hole drilled in fiberglass lacks the integrity to hold-up over long term stress and vibration.

My suggestion is to plan your panel footings at a width such that they fall within the OH cabinets where you can install a proper load-spreading washer or bearing plate for a through-bolt with nut that's not visible in the trailer's living space.

If your panels aren't wide enough for that span, install crossbars which are and fasten the panels to those

Exactly. I've used rivnuts in high stress situations and they held up well. But they wouldn't work well in this situation.

I've used the cross bar solution, with the bolts hidden in the overhead bins. Absolutely the strongest way to go.

Ron

[Iowa Dave]

Another vote for having your stand off stabilizers anchored in the cabinets. That’s the way Escape used to do it on aftermarket installations. Worked perfectly on our 19. You do not notice the nut and washer.
Iowa Dave

[Viajante]

If you go with through bolting then you don't need the vhb tape.

AM Solar, which is recognized as the leader in rv solar panel installations, uses vhb tape alone. In cases where vhb tape won't work (curved or textured surface) they recommend well nuts. Watertight and vibration dampening. If you don't want to drill through the headliner then consider vhb tape + well nuts as an option.

[Perry Butler]

Originally Posted by Hawkeye Ed

Does anyone have any experience using blind (pop) rivets or rivet nuts (rivnuts) for an installation on exterior camper fiberglass?

I'm installing solar panel mounting feet on my 5.0's roof with 3M VHB tape but I'd feel more comfortable adding a mechanical fastener into the fiberglass. I'd rather not drill all the way through the interior headliner to install an interior washer and nut. So I'm thinking I might be able to install a blind rivet or a rivet nut through the fiberglass from the outside without needing to have anything showing on the interior headliner.

My experience and opinions.

Pop rivets work well when there are many holding, but not so well with only one or two.

I removed the panel that came with our Bigfoot. It was mounted with one poor rivnut and only Dicor to hold the mount. It was located behind the AC so may have stayed on forever, but who knows. The only way to remove the panel was to completely remove the mount. The rivnut used fell in the fiberglass after removal, but I'm not mounting the panel in the same place and will cover the holes with Dicor.

I want a mount that allows removal of the panel without removing the mount, so for current install I'm using AM Solar panel mounts. I also don't ever want a flat mount again, but angle the panel so water does not stay on one side of the panel collecting dirt. Using the AM 5 hole mounts I can give the panel just enough tilt so water doesn't accumulate on our 24v 200 watt Rich Solar panels. In our north/south install, the mounts on the outside are in the lower hole and the mounts in the trailer's center are in the third hole to get enough angle for water to leave immediately so no water/dirt is over the cells.

AM Solar uses VHB tape and they claim that if you prep properly it will stay attached. Our front panel is in the direct wind, but north/south. In that orientation AM Solar advised me to use the stainless steel screws they sent with the mounts (2 screws per mount) on the front of trailer set of mounts. They feel rivnuts are inferior to screws when used with fiberglass. As long as the screw holes are not too big screws will work great. Even though Bigfoots fiberglass is much thicker than Escapes it's still not thick enough for rivnuts.

The adjustability of AM Solar mounts is fantastic, but at $80 plus shipping, for four mounts they are expensive. In my Adding 300 Watts Solar To Our 5.0 thread I built my own mounts for about $50 in aluminum/SS bolts and a few runs to Rochester, the AM solar mounts are equally as good (despite four holes in our roof for the front mounts) and the time saved is worth the $160, plus shipping, for mounts for two panels. The rear panel is behind the AC in the north/south orientation, so no screws will be needed.

I also have purchased a set of AM Solar's tilt bars so I can clean underneath the panels ever year or so. I'll be applying Zep Floor Polish this Monday or Tuesday, and I can just tilt the panel up to apply.

DO NOT MOUNT VHB TAPE ON A WAXED SURFACE! Clean your area where the VHB tape will be applied with a good cleaner first, flood any cleaning residue away, use a light sandpaper to remove any wax, giving better surface area for the VHB tape to adhere, flood the sanded dust away, and finally use 90% rubbing alcohol on the attachment spot immediately before placing the panel/mounts on your roof.

After a couple of hours, or the next day, make sure to apply Dicor self-leveling sealer. If water reaches the tape it WILL separate.

Food for thought,

Perry

[BobG]

Originally Posted by Centex

.... I would not use either for a blind structural fastening into a fiberglass shell.

My suggestion is to plan your panel footings at a width such that they fall within the OH cabinets where you can install a proper load-spreading washer or bearing plate for a through-bolt with nut that's not visible in the trailer's living space.

If your panels aren't wide enough for that span, install crossbars which are and fasten the panels to those.

Just one person's opinion for your consideration, Good Luck and Have Fun! ...

I agree with this and what others have said. I have a 21NE without an absorption refrigerator vent.

I did install a rail on both sides of the roof using 1/2" SS bolts, backing plate of 2" x 2" x 1/2" HDP and SS fender washers inside the cabinets. I peeled back the foam and drilled through the wood that the cabinets are attached to. I used 3M (maybe 5200) between the backing plate and ceiling and in the bolt holes. I drilled the holes from top of trailer after snapping a straight line.

There are 5 bolts on each rail. I don't have an absorption refrigerator vent.

You could then add cross bars on top of the rails and attach the solar panels to the cross bars. Lack of experience kept me from considering the cross bars. Instead, I used AM Solar's hardware attached with VHB tape for other attachments.

[Keith3]

We replaced just about every pop rivet in our Scamp 19. They work great, but each one has an acorn nut on the inside to increase the bearing surface. And there are tons of them. I would not recommend a blind pop rivet in fiberglass as a strict element without a lot of testing.

[GregWCIL]

As others have said, neither pop rivets or rivnuts will work in fiberglass. They only work in metal. Also all rivnuts I’ve used were rated for much thinner material than the Escape fiberglass which is usually a quarter inch or thicker.
Drill through inside the cabinets and through bolt, preferably with a good 5/8 or 3/4 inch plywood block to distribute the load. I also used liquid nail glue between the fiberglass and block to fill the voids caused by the uneven/rough fiberglass. It took a lot of measuring to get it right. In some cases I was able to drill through the plywood Escape had glued to the fiberglass to mount the overhead cabinets.
Dicor between my brackets and the exterior fiberglass plus dicor around the brackets and bolts should prevent any leaks.
I called 3M to ask about VHB tape and they flatly said they do not recommend it for attaching outside items to moving vehicles. Maybe it’s lawyer talk but there is pretty large liability if a panel would detach. And there have been cases of that happening. No one wants anyone to get hurt. Do it right.

[Perry Butler]

Originally Posted by GregWCIL

As others have said, neither pop rivets or rivnuts will work in fiberglass. They only work in metal. Also all rivnuts I’ve used were rated for much thinner material than the Escape fiberglass which is usually a quarter inch or thicker.
Drill through inside the cabinets and through bolt, preferably with a good 5/8 or 3/4 inch plywood block to distribute the load. I also used liquid nail glue between the fiberglass and block to fill the voids caused by the uneven/rough fiberglass. It took a lot of measuring to get it right. In some cases I was able to drill through the plywood Escape had glued to the fiberglass to mount the overhead cabinets.
Dicor between my brackets and the exterior fiberglass plus dicor around the brackets and bolts should prevent any leaks.
I called 3M to ask about VHB tape and they flatly said they do not recommend it for attaching outside items to moving vehicles. Maybe it’s lawyer talk but there is pretty large liability if a panel would detach. And there have been cases of that happening. No one wants anyone to get hurt. Do it right.

This week I removed an older panel on our roof that was attached with Dicor between the bracket and the fiberglass and one rivnut. What a joke! The dicor easily pulled off the fiberglass and I mean really easy. The difference between Dicor and VHB tape is day and night. Don't confuse the two.

I've used VHB tape in the past and when properly applied and sealed from the elements holds. I used AM Solar's panel mounts with VHB tape and did add a screw, just because. The panels are also mounted north/south so less panel in the airstream. That's why I chose small 100 watt panels in the east/west configuration with much more VHB tape area on our 5.0. There's a couple of good reasons ETI's VHB mounted panels failed: a long panel in the east/west configuration, and improper prepping.

Enjoy,

Perry

[WillyB]

We used VHB tape for some time in one of our products. During sales training demonstrations I would hand someone a big pry bar and tell them to remove the panel. Every time after destroying the panel they gave up well before the panel was even 5% removed.

VHB can be a great solution but the CORRECT VHB with BOTH mating surfaces PREPPED INCORRECTLY will fail miserably.

[Perry Butler]

Originally Posted by WillyB

VHB can be a great solution but the CORRECT VHB with BOTH mating surfaces PREPPED INCORRECTLY will fail miserably.

Do it right, or don't do it at all. AM Solar told me to remove the wax with medium sandpaper and they don't like an an east/west install with >50" panels.

Enjoy,

Perry

[GregWCIL]

Originally Posted by Perry Butler

This week I removed an older panel on our roof that was attached with Dicor between the bracket and the fiberglass and one rivnut. What a joke! The dicor easily pulled off the fiberglass and I mean really easy. The difference between Dicor and VHB tape is day and night. Don't confuse the two.

I've used VHB tape in the past and when properly applied and sealed from the elements holds. I used AM Solar's panel mounts with VHB tape and did add a screw, just because. The panels are also mounted north/south so less panel in the airstream. That's why I chose small 100 watt panels in the east/west configuration with much more VHB tape area on our 5.0. There's a couple of good reasons ETI's VHB mounted panels failed: a long panel in the east/west configuration, and improper prepping.

Enjoy,

Perry

I didn’t mean to imply I used Dicor for any bonding. I thru-bolted so Dicor was simply a water sealant.
VHB is very good but the 3M rep told me it can come loose under specific types of shear loads, thus they can’t recommend it- not knowing how each application may vary in loading and quality of install.
Frankly, none of us have the capability or resources to test what wind loads are on panels. I thus chose to error on the side of stronger mounting. I also went to great lengths to install a fairing to direct airflow over the panels and not under. I plan to give those details on a separate thread.

Edit to add: Why AM Solar goes against 3M’s advise puzzles me.

[Perry Butler]

Originally Posted by GregWCIL

Why AM Solar goes against 3M’s advise puzzles me.

Perhaps AM Solar's 3M rep says otherwise. Your rep could also base his advice on improper prepping. There could be 100's of reasons, but AM Solar has had success. The claim none of THEIR installs has ever blown off. I'm sure some of their mounts installed incorrectly by their customers have blown off, but people do things incorrectly all the time.

We each have the ability to make our own choices based on the data we use. I'm fine with VHB tape, your not. That's OK!

Enjoy,

Perry

[AdobeMatt]

Common pop rivets typically have a matching aluminum backing washer. Assuming you can reach the inside, you might need a helper to hold the washer as the rivet is drawn from the outside.