Dicor vs 3M for Panel mounting

[Blues Driver]

Has anyone used Dicor as an adhesive without screws for rooftop panel mounting. I was talking recently with an RV service tech who preferred the Dicor for ease of use and offering some cushion between the mount and the rooftop. I plan to use aluminum L shape mounts on the fiberglass roof for panels approx. 40" x 66".  I am concerned about the roof curvature making adequate contact with the flat mount.
Thanks,
Pat

 

[Kevin Means]

If you're trying to avoid drilling holes in the roof, I'd recommend using VHB tape to secure your panel, then use Dicor to seal around the edge of the tape. Dicor is good stuff, but it was not designed to hold something as large as a residential solar panel in place while driving in gusty winds.

Kev

 

[Domo]

If you are referring to Dicor self-leveling sealant - I certainly do NOT believe it is intended to be an adhesive.

On the roofs of my current MH and my old pull-behind trailers I'd:

Pre-drill holes
Drive the mounting screws in 3/4 of the way and remove them
Clean up the dust/dirt/chips surface
Lay down a "gasket" of butyl rubber (comes in 1" wide and 2" wide rolls with paper between layers so it won't stick to itself - kinda similar to double-back tape  - but thicker 1/8-3/16")
position the mounting plate
Coat the mounting screw threads with some Dicor and insert the screws and gently tighten in an appropriate pattern (star, cross, etc.)
Remove excess (squieezed out) butyl rubber with fingers or putty knife
Clean the exposed screw heads and mounting flange and adjacent roof (yes, again)
THEN, apply dicor around the edges and over each screw head
Finally, smooth the dicor (somewhat) with a wet finger (don't work it too much)

Bottom line is that I don't want to spend a lot of time on the roof fixing a leak - nor do I want to have to repair the inside of the rig due to a leak - nor do I need to have DW discover a leak...

I've never had a leak from anything I've mounted; solar panels, solar wire entry cover, fantastic fan covers, replacement fan assemblies, fridge roof vent, plumbing vents pipe penetrations and caps, roof ladders/racks.

IMO - ANY "tech" that says he just uses a sealant to affix something to the roof is just lazy and wanting you to drive off the lot to end his warranty period.

Okay - after saying all of that - I do know that there "could" be a wonderful new product (such as many from 3M) that can stick ANYTHING to ANYTHING else forever - in which case, my apologies for abusing your tech.

 

[Blues Driver]

Thank you both. You have confirmed my thoughts.
What thickness is the "plywood" (2010Winnebago Vista) or what have you found? No point in using an excessively long screw. 
My attraction to the 3M adhesive is being able to use it alone, no screws. As  I'm planning large panels, 40 x 66, and the screws might be good insurance. I know from experience what a piece of plywood that size can do in the wind.
I am also concerned about the roof curvature. Domo, you called out the 3M thickness of 1/8 to 3/16" and that might adjust to  the curvature on a 2 or 3" mount base.
AM solar has a video re panel mounting showing the use of the 3M product alone. Their videos are worthwhile.
Thanks again,
Pat

 

[Domo]

That was the thickness of the Butyl Rubber, not for a 3M product.

If you are going to simply tape (with some 3M product/adhesive) to a membrane roof (such as rubber or EDPM), I'd be very concerned that the added weight/profile and wind resistance could conceivably pull hard enough to start separating the adhesive that is hold your membrane to the plywood. I've seen membrane roofing bunch up in the past - some adhesives that are used under them do not become a solid and can slip and slide.

My preference (as an engineer and as a remodeling contractor) is to ALWAYS attach to structurally sound members, rather than to a secondary attachment. (e.g., don't attach a deck to your siding - attach it through your siding into your studs/joists/beams.)

Please consider how secure your membrane is before skipping  "real" mechanical fasteners (you know, the kind that have been used for thousands of years successfully).

I have a fiberglass roof on my MH and I know many folks that use the doubleback 3M tapes. The fiberglass is very intimately bonded to it's substrate and has the rigidity and stability to withstand the turbulence of travel - however, on my rig - I'll still use fasteners and get to the actual structure so that I can sleep at night and travel down the road knowing I will not have something fly off the roof and hit an innocent on the road.

Okay - that's my paranoia speaking. Please understand we all volunteer our thoughts to help everyone be safe and enjoy travel.

 

[PJ Stough]

When I put my first two panels on in January 2011 I used 3M Quick Set adhesive, and one screw per attachment.  The screw was only to hold the panel in place while the 3M set up.

It is my observation that there is not near as much wind buffeting on the panels as one might imagine, as I drove from Iowa to Arizona with one of the attachments not connected to the panel on the leading edge of the front panel, and the panel never moved, or bounced.

 

[Frank B]

>It is my observation that there is not near as much wind buffeting on the panels as one might imagine<


Exactly.


I used L shaped brackets for the six panels on the roof of our unit. I had 6 brackets per panel, and two #12 screws in each bracket. Way overkill.


There is another issue if panels are attached too close to the roof. Heat builds up, and efficiency of the panel goes way down. It is my understanding that they should be mounted up above the roof to some extent to allow for cooling.

 

[Gary RV_Wizard]

I'm not familiar with a 2010 Winnebago, but typically the roof substrate is a thin sheet of luan, maybe 3/16", just enough to provide a smooth surface for the waterproof skin above it.  Not a lot of material for a screw to grab and the chances of being over a thicker rib are slim.  My strategy when screwing something to an RV roof is to use short screws with a coarse thread in size #10 or #12. That seems to provide a decent grip in soft, thin material.

The adhesive you apply is mating to the roof skin (fiberglass in this case), so you are also relying on the adhesive that holds the skin to the substrate.


As PJ says, there  really isn't much direct wind force there when driving - the wind mostly flows well above the roof surface. A wing effect creates a low pressure area along the roof surface and triesto suck things upward rather than pushing them back along the surface.  You are more likely to have wind issues when parked in a storm.

 

[Boat Addict]

For a wide variety of jobs requiring sealant that bonds and hold pick up some Loctite Roofing and Flashing Sealant . it used to be a PL product, but has been bought out and sold under the Loctite label now.  Its black. I use it religiously on boat projects to even laminate  parts without fasteners for in water use.  But it makes a great gasket. Put it in place and let it cure before completely tightening up any fasteners. Then run the fasteners back out and put a dab on the screw and run it back in place. Its cheap too, about 6 bucks a tube and readily available at most of your big box stores.
It  has the same working properties as 3m 5200, but about 15 bucks retail cheaper too.