Which adhesive caulk for solar panel mounts??

Almot wrote:

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According to my friends who used 5200, it's hard to remove, much harder than 4200.

4200 not only cures soft-ish but also cures very slow. It has low density and flows out on sloped surfaces, don't expect it to behave like a usual caulk.
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I would definitely use 3M 5200 if that was the only thing holding the brackets down, especially as others have had success with this on fibreglass. And as also mentioned, 3M adhesive tapes may be strong enough.

But as my brackets used 3 screws each, 4200 has worked well so far with no apparent UV deterioration after 3 years. It did take a day or so to cure and is not rock hard. But I see the new brochure lists it as "4200FC" which must imply "fast-cure". Pretty sure the stuff I used did not have the FC.

If no adhesive properties are needed, just sealant, I've use both Dicor and Geocell, and other polyurethane sealants with good results.

5200 comes in a fast cure version too, though it should be called slightly faster.

It is not that difficult to remove, if one uses the right tools.

I've had some holding some MC4 cables to my painted fiberglass roof since 2011. its cracked from UV light exposure, but I cannot break the bond with my fingers.

brulaz wrote:

both 4200 and 5200 are referred to as "adhesive sealants" in 3M's brochures. 4200 in particular is described as an "excellent adhesive sealant".

In manufacturer's brochure I wouldn't expect anything less :)

According to my friends who used 5200, it's hard to remove, much harder than 4200.

4200 not only cures soft-ish but also cures very slow. It has low density and flows out on sloped surfaces, don't expect it to behave like a usual caulk.

Their "marine" rating has little to do with adhesion to FG. It just means that it doesn't deteriorate fast in seawater and UV exposure.

MEXICOWANDERER wrote:
SFVdave,

The isn't any different and DuPont 5200 would be my first choice. I used it on the brackets of my Kyoceras and 31 years later the stainless brackets ar just fine.

There is nothing wrong with cutting 6" X 6" 16 gauge steel pads for panel mounting. Glue the pads to the roof with 5200 laying a brick on top for compression. I used stainless RivNuts and stainless bolts cut exactly to the right length, then applied Red Loc-Tite to those bolts. They have withstood hurricanes and even the reported 145 mph gusts we got down here with Gilberto.

Just read this post and had to reply. I installed solar panels on my Class A 12 years ago, not wanting to Potok holes in the roof I used 1" x 2" aluminum channels, and glued them down with 5200. It was still holding, when I traded it, and never any problems with the roof!

I used 3M 4941 VHB tape under the brackets. I had no concern about water or UV as all exposed areas are covered with Dicor.

Almot wrote:
3M 4200 is a sealant, it cures somewhat soft. Adhesion, particularly to FG, is a different matter, not everything adheres well to cured polyester resin but this is not crucial when sealant is used to seal rather than to hold.
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Yes, 3M 5200 is a stronger adhesive, but both 4200 and 5200 are
referred to as "adhesive sealants" in 3M's brochures. 4200 in particular is described as an "excellent adhesive sealant".
multimedia.3m.com/mws/media/811831O/3mtm-adhesive-sealant-brochure.pdf

The brochure has a comparison of their adhesive properties.

3M also markets 540 polyurethane and 730-755 hybrid products that they only refer to as "sealants", not "adhesive sealants". I suspect these are more similar to Geocell and Dicor sealants.

As both 3M 5200 and 4200 are marketed for the marine market, I'm sure they adhere well to fibreglass.

SFVdave,

The isn't any different and DuPont 5200 would be my first choice. I used it on the brackets of my Kyoceras and 31 years later the stainless brackets ar just fine.

There is nothing wrong with cutting 6" X 6" 16 gauge steel pads for panel mounting. Glue the pads to the roof with 5200 laying a brick on top for compression. I used stainless RivNuts and stainless bolts cut exactly to the right length, then applied Red Loc-Tite to those bolts. They have withstood hurricanes and even the reported 145 mph gusts we got down here with Gilberto.

Lowes has 3M 5200 marine adhesive caulk in a red tube and I see online most are in a blue. They do say Marine 5200, wonder what the difference is?

3M 4200 is a sealant, it cures somewhat soft. Adhesion, particularly to FG, is a different matter, not everything adheres well to cured polyester resin but this is not crucial when sealant is used to seal rather than to hold.

The RV manufacturer recommended hollow wall anchors that flare out when tightened.

Sounds like well nut.

Hitting the rafters is a good idea too, when practical.

kaz442 wrote:
3M 4000UV it's a marine adhesive and caulk. It's made for bedding cleats and such on boats above and below water line. It's UV resistant and has a tensile strength of 500psi. They also make a 5200UV but that's overkill.

Good choice. I used 3M 4200 and it's also holding up well.

These 3M products are very adhesive, as well as good sealants. 3M 5200 is extremely strong.

AFAIK the other products, Dicor, Geocell, are less adhesive but also good sealants.