Mike C.

I spotted this over on Pelican

"any suggestions of what went wrong? I resealed my hatch and did it according to the Clark's writeup. I completely stripped off the paint off the frame and glass. Cleaned both and primed them with the 3-M primer and used the 3-M sealant. I had a good fit and made certain the bead of sealant was good. I even used ratchet straps to apply some pressure as the sealant cured. I only waited about 30 minutes after priming as per instuctions, and alllowed the sealant to cure for 48 hours before removing the hatch. It's been about 6 months now and it's already beginning to seperate at the top. I read one post that the best thing to do is to not use the primer on the glass and paint a cover strip around the glass on the outside allowing for a better bond on the glass. Any suggestions?"

This isn't too encouraging.. Anyone in the auto glass business who can tell me if roughing up the glass will help with bonding? I mean like 400 grit paper..

hobiecat

I'm curious about this too....just started thinking about doing this job myself.
Could there be a "professional" grade of 3M sealant? Maybe that's the
difference?

FRporscheman

My dad was in the auto glass business for over a decade. Don't sand the glass, because it's tempered and it will shatter.

The best ways to keep it from unsealing are to use an industrial type urethane, and to make sure the surfaces are both clean, I mean like clean enough to perform surgery on. Also, don't use really stiff hatch struts. That said, I tried resealing a hatch myself and it separated in like 1 month. The hatch struts are brand new.

SpecialtyConcreteCoatings

I don't have any knowledge regarding auto glass, but I am familiar with many different types of 'caulk'. The company I work for does, among other things, waterproofing. We often trace leaks on houses back to windows. Some leaks are remedied by caulking around the perimeter of the glass. For this application we use Dow Corning 999-A. It is the ONLY silicone based sealant we use. It contains acetic acid that etches the glass resulting in excellent cured adhesion. It will also bond well to metal. I haven't read up on the hatch reseal process, although I do need to do it to my hatch soon. The 999-A would be my choice. I believe this would provide a better glass to metal seal than urethane. Both surfaces, prior to application, should be cleaned with Xylene or something similar.

Maybe I'll get off my *** this weekend and give it a try. I don't know if the 999-A is readily available, but I have accesss if others are interested.

Mike C.

Well I did a bit more research myself and while reading the fine print on the urethane primer adhesive (3M part no. 08682), it appears that 3M priming bare metal is a no-no. It says "can be applied to fresh bare metal scratches on the pinch weld to prevent corrosion. Note: When excessive abrasive cleaning is required, prime metal with a 2 part epoxy automotive primer and allow to cure properly. Apply 3M Single Step Primer to repaired area and allow to dry for at least 10 minutes". Now the way I read this, it's saying do not apply the 3M directly to bare metal. I believe this guy primed the bare metal with the 3M. Seems a bit far fetched that the primer sticks to metal better than the primer/urethane (and urethane sticks better to automotive primer than bare metal) but I suppose it's possible.

As for the silicone, I have no doubt it would easily solve any water sealing problems but I suspect it doesn't have the strength of the urethane, which seems to be highly stressed in this application. (tensile strength 1200 psi, 700% elongation, overlap shear strength 65 psi @ 6 hours and 500 psi @ 48 hours - I'd have to research the SAE J1529 spec to see what the overlap tests really mean). Any numbers for the 999-A?

SpecialtyConcreteCoatings

Is a structural bond required?

Mike C.

I would say absolutely. If it were a stationary peice of glass in a fixed frame I would say no but in this case separation of glass & frame always occurs first at the hinge areas and the glass actually lifts away from the frame. The hatch struts (especially new ones) put a lot of stress into the frame, you have to push the hatch down with more force to close it and, I believe, this puts the upper part by the hinges in tension as you push down on the rear of the hatch. The frame itself is a flimsy piece of aluminum- the glass must be fully bonded to make the whole thing structurally rigid.

AR10

I think a lot of these separations are people caused. If you are in a hurry and slam the hatch down it puts
way too much pressure on the glass. Take it easy and it will last a lot longer. My $.02

boston951

After 20+ years of use delamination can simply occur.

Mike C.

Well mine lasted 20+ years and I'm sure I didn't abuse it. I do have trouble believing that a reseal with the same stuff the facotry used (urethane) can only be expected to last 1 - 2 years. Not if you do it right. And 3M has been around and making this stuff for a long time - they are not a fly-by-night company.

billthe3

Why not attach the glass to the frame using some 3M VHB tape? It is waterproof, and it insanely strong (they have used it to hold exterior panels on sky scrapers). Then just paint a black strip on the outside of the frame to cover it up. Or stick a bead of sealant around the outer edge of the tape to make sure it is water tight.
http://solutions.3m.com/wps/portal/!...www.3m.com/vhb

Their acrobat advertising thing about the tape - shows all the buildings and other things made with it.
http://multimedia.mmm.com/mws/mediaw...666_uxCOrrrrQ-

Mike C.

I'll look into that, sounds interesting.

ritzblitz

I was that VHB tape on Modern Marvels. They literally pulled a train with it haha.

I'm no expert on sealing anything. Would RTV work?

billthe3

^ Yeah, thats where I saw the vhb tape thing as well. It sounds like it should work excelently as long as you are able to cut it correctly.

Airflite40

That tape is probably expensive though....