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Old 03-17-2023, 06:39 PM   #1
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Join Date: Jun 2012
Location: Salt Lake City, Utah
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Best caulk for mounting roof rack

My fiberglass penthouse top is leaking and the water mostly comes out the drivers side front corner and moisture wicks into the night shades as well as creeping down the canvas. It has had minor stains there and on the passenger side from leak when owned previously.

The leak got much worse the past year when the entire original roof rack was ripped off clean in a wind storm. I had a thin coat of Rhino-like material put on top of the fiberglass roof at that time, then had entirely new tracks, rack, solar and rocket box remounted. It started leaking more soon after that.

I have been systematically caulking holes on the fiberglass roof and about the only option left is where the right and left tracks for the rack attach to the roof. The drill holes from the new and previous job are only slightly outside where the canvas attaches to the roof, but I am almost certain now these are the culprits, a poor caulking job around the bolt holes when they were installed. You can see he ran a bead, but it still leaks. The local specialists are nervous about messing up my roof even worse trying to get the old tracks off without damaging the fiberglass beneath.

I want to caulk all around the edges of the metal tracks and also make sure the recessed (bad design folks) bolt holes are caulked but still accessible so I can adjust the hardware above.

What would you use to caulk these parts? I have previously been using 3M Marine Adhesive Sealant 5200 for small repairs.

Also, any quick ideas for repairing small holes in fiberglass that doesn't use fiberglass? Holes are the old bolt holes in the top- I just want to plug them.

Thanks for the advice.
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Old 03-18-2023, 09:41 AM   #2
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Location: VIRGINIA
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I liked Marine Tex for small repairs to fiberglass. It's not cheap. 5200 is great as long as you like it permanent. I came to like butyl rubber tape for bedding down fittings. It's much less messy than 5200.

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Old 03-18-2023, 10:01 AM   #3
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Just thinking out loud -- what about making fiberglass (round ?) discs as plugs to cement into the holes - using the marine grade cement ?. Or use the ridged plugs that attach the PH rubber gasket to the fiberglass top ? Cut off excess plug length (ribbed part) and cement with 5200 ?
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Old 03-18-2023, 06:20 PM   #4
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Location: PNW or maybe Baja Sur
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Another vote for marine tex....Also many polyurethane sealants will do the trick for sealing bolts. Also you might look at 3M 4200. 4200 is slightly more conducive to allowing disassembly. Sikiflex is a good brand available at Home Depot in the roofing area...and am>>on of course...
A super common point of entry is the track fasteners if they were inside the canvas...If outside it really shouldn't matter because the weep outside the cabin...Caulking the outside of anything is not a very good band aid...
Have your looked closely or re-bedded your roof bolt thru fasteners with the large washers? Check the roof to canvas seal closely...If you are describing fasteners that are outside how is the moisture getting inside?
Pac NW and warmer places
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