Fiberglass Sunroof Flange Repair

Posted onAuthor435795szerszen

Searching through the online forums, the most common statement associated with a leaking sunroof is a worn sunroof seal. This sounds logical, as when you do not want water leaking, improve the seal. This is a great idea, although the sunroof seal is not meant to prevent all moisture from passing through, that is why the sunroof frame has four drain holes. Not thinking beyond what I have read, I decided to replace the seal anyway. When removing the old seal, parts of the flange the seal straddles came off with the seal in multiple pieces. I suspect the flange was cracked from the sunroof being dropped or repeatedly resting against the corners. The sunroof is definitely not light or easy to handle and the pressed fiberglass is very brittle.  

Damaged Flange after Seal Removal

Leaving the sunroof as is with the two broken section was not a good option. Neither was attempting to glue the fragments back in place as the break was not clean and would likely fail again. I decided to attempt a permanent fiberglass repair. The idea would be simple, lay up a couple plies of fiberglass to rebuild the flange while tying into the existing flange. Just enough to hold things together but not so much to interfere with the seal. The problem with laying up plies without an existing surface is that it is difficult to maintain the correct profile while the plies cure. Manufacturing a tool surface to lay the plies up against would be more effort than its worth. Looking for a better solution I reached out to a friend with a significant experience with composites. He recommended using Bondo Glass to reshape the flange, which would then serve as a base for the fiberglass plies. Bondo Glass is a filler that is reinforced with short strand fiberglass making it easy to work with while having decent strength due to the fibers.

Damaged Flange Prepped for Filler – Location 2

I used basic painters tape to make a dam to support the filler. I added a fairly large amount of filler as I planned on shaping it after it cured.

Built-up w/ Bondo Glass – Location 2
Built-up w/Bondo Glass Inside – Location 1

After cure I cut down the height and used a diamond ball end bit to shape the filler. I shaped it to be thinner than the desired final flange thickness to allow for a couple plies of fiberglass.

Trimmed to Flange Height – Location 1
Prior to Shaping – Location 1
Post Shaping – Inside Location 1
Post Shaping – Outside Location 1
Post Shaping – Location 2

I laid up 3 plies of fiberglass on the inside, tying in the bondo to the undamaged structure, and one ply on the outside running the length of the flange only. Flashbreaker tape was used to apply pressure to the single outer ply during cure. Three plies in theory sounded like a good idea, but without applying positive pressure to help consolidate the plies and squeeze out the resin, the final thickness was greater than expected. I had to remove some of the material after it fully cured. I removed enough material to ensure the seal would install on the flange without too much pressure while sitting at the same height as on the unrepaired flange.

Template Fiberglass Ply
Inside Repair Plies Set – Location 1
Fiberglass Plies Curing at Both Locations
Detail View of Inside Plies – Location 1
Detail View of Inside Plies – Location 1
Outer Ply with Flashbreaker Tape
Post Cure and Trim – Location 1
Shaping Removing Excess Material on Inside – Location 1
Completed Repair Prior to Paint – Inside Location 1
Completed Repair Prior to Paint – Outside Location 2
Completed Repair Prior to Paint – Outside Location 1

A coat of paint and the sunroof was repaired. It has been three years since the repair was completed with no issues to report. It’s good to note that the real cause of my leaking sunroof was actually a pinched drain hose on the rear driver’s side. The drain hose is routed with the sunroof mechanism. Where the cable makes a turn at the sunroof, it was pinching the hose against the frame.