Tj hardtop repait

[woody367]

Hello new to the site, I was told by a member of a Jeep site that "jscherb" was the man to ask on here. I just bought a hardtop for my 97 wrangler TJ and it has some damage to it at the rear vent area cracked right thru. The piece is almost all the way off.. I was told it is not fiberglass but SMC and would require special resin for the repair, I found this product but not sure how good it is or how much to get. 3M-04248-SMC-FIBERGLASS-REPAIR-ADHESIVE-35-URETHANE-TECHNOLOGY- I am also not sure the best way to prep and do the repair. Was hoping soneone could help me out.I will try and post a photo of the damage. Any help would be greatly appreciated. Also what the best place to get a new complete seal for the top.
Thanks

 

[jscherb]

I've used urethane adhesives quite a bit but in my experience they're not as good as fiberglass for a repair like the ones you've got to do. They do bond well to fiberglass/SMC, but two things are lacking:

- A repair using SMC-compatible polyester resin and fiberglass cloth or mat will be stronger than a urethane adhesive repair because the repair will be reinforced with new fiberglass. A urethane adhesive repair will only rely on the bonding strength of the adhesive but a fiberglass repair will rely on both the strength of the bond of the polyester resin plus the reinforcement of the embedded fiberglass cloth or mat. It is possible to reinforce urethane adhesive joints with a doubler plate bonded behind the repair, but even so fiberglass makes a better repair in my experience.

- Urethane adhesives don't sand or finish well, so you can't easily make a repair that won't be visible on the exterior of the hardtop. They're really a "glue" where a fiberglass repair is the same material as the hardtop and is workable in the same way.

Because Jeep hardtops are made from the SMC variant of fiberglass, you'll need to use an SMC-compatible polyester resin, at least for the layer that bonds to the top. It turns out that once the first layer of SMC-compatible resin has been applied to the repair area (ideally with fiberglass matt embedded in that first layer), subsequent layers can be done in less expensive/more easily worked ordinary polyester resin.

Ideally what you'll want to do it gain access to the inside of the repair area and do the main repair/reinforcement on the inside. I haven't worked on a TJ hardtop for a while, but I believe the area you need to repair is double-walled, so you'll need to cut an access hole in the inside wall so you can get to the inside surface of the outer wall. If you cut the access hole carefully you can bond the cut piece back in place after the main repair is done and use some body filler to hide the fact that you ever cut the access hole. Because you say "the piece is almost off" this suggests that the repair needs to be very strong so doing a repair just from the outside surface of the hardtop probably won't be strong enough to last long term.

Continued next post...

 

[jscherb]

I recently did a repair in a JK Freedom Panel which should illustrate the basic techniques to use on your repair. Here's the Freedom Panel damage:

The fiberglass is cracked to the point where it's no longer structurally sound and some of the outside skin is actually broken off and missing. The panel is double-walled, so access needs to be gained to the inside to properly make the repair. It turns out that in this case the inner wall was also cracked and broken so with a little more cutting I was able to separate the inner and outer shells for access to the inside of the outer shell.

In this next photo I've applied several layers of fiberglass mat soaked in SMC-compatible resin to the inside of the repair area. I've used masking tape on the outside to contain the resin and act as a form for replacing the parts of the skin that were broken away and lost in the accident.

In this case, since the repair area was small and mostly non-structural, three layers of fiberglass mat soaked in SMC-compatible resin was enough to make the repair, and after those were applied I closed the inner skin and bonded that back to the outer skin with more SMC-compatible resin. The process on your repair would be a little different, since your repair is definitely structural I'd add a few more layers of resin + mat extending out several inches from the crack.

Once that's cured, the cracks in the outer skin are mostly cosmetic; the structural repair was done on the inside, so the exterior can be cosmetically repaired with body filler, ideally an SMC-compatible filler. Best practice is to grind/sand the crack so that all of the loose fiberglass is removed and a "valley" if made in the surface to put the filler in. Here's the valley sanded along the crack area:

I then applied narrow strips of fiberglass mat soaked in SMC-compatible resin to the crack area:

Having done that, I used body filler to fill any remaining imperfections, sanded it smooth and painted it with primer followed by MOPAR hardtop touch-up paint.

 

[jscherb]

Almost nothing is "too broken" to be repaired using similar techniques; a while back when I was just starting my conversion of a factory JK hardtop to modular I picked up a broken side panel from a hardtop. It was missing a lot of the top edge of the panel but other than that it if repaired would make a good modular side for my project. It also had a large crack along the bottom edge. This repair was a little more advanced than the one above; for the Freedom Panel I was able to use masking tape as a form to make the repair of the missing fiberglass, in this case a lot of area was missing so I used a wooden form as a "mold" for the area to be replaced. The bond for the new area, and the repair of the crack at the bottom of the panel, were done using the same materials and techniques as the Freedom Panel repair though. Some before and after photos...

Anyway... the damage to your TJ hardtop is definitely repairable, and a permanent structural repair can be done using the techniques described above, particularly:

- Gaining access to the inside of the repair area so the structural repair can be made from the inside. If you cut an access hole in the inside skin carefully enough it can be replaced after the main repair is done and with a little body filler and paint made almost undetectable.

- Using SMC-compatible polyester resin along with fiberglass mat, applied to the inside of the repair area in several layers ending several inches beyond the crack

- Creating a valley along the crack, doing a first layer repair with SMC-compatible resin and strips of fiberglass mat followed by body filler, sanding and paint.

I'm happy to explain anything further if I haven't explained it well enough in the posts above.

Good luck.

 

[ratled]

While it is a JK and not a TJ I would expect them to be similar, this video shows these guys fix a hard top

ratled

 

[woody367]

Thank you for all the great information, the repair you described is kinda what I was planning to do.
I do not need an access hole, as the hole for the vent gives me all the room I need. Could you please recommend what SMC resin and body filler to use. I already have fiberglass kits to use.

Thank you again

 

[jscherb]

I've used these two SMC-compatible polyester resins with good results:

All Resin: http://uschem.com/index.cfm?page=productDetail&id=143

Evercoat SMC Resin: http://www.evercoat.com/product-detail/base-part/100864/us/

An alternative to SMC-compatible polyester resin is to use epoxy resin. A good choice in epoxy is West System G/Flex: https://www.westsystem.com/specialty-epoxies/gflex-650-toughened-epoxy/. Epoxies like G/Flex will actually bond slightly better to SMC fiberglass than SMC-compatible polyester resin, although both types of resin work well. Epoxies generally don't sand as well as polyesters but since most of your repair will be inside that's not an issue.

Evercoat makes several fillers that are compatible with SMC, here's a list of all of their fillers, the ones that are SMC compatible are say so in the description text: http://www.evercoat.com/reinforced-fillers/us/ and http://www.evercoat.com/premium-fillers/us/

You can use ordinary body filler on top of a repair made with SMC-compatible resin though, check the photo I posted of the exterior repair of the crack in the Freedom Panel: I put a base of SMC-compatible resin with fiberglass mat into the crack, and the filler I used on that repair was ordinary filler, I happened to have Shark Bite on hand because I use it a lot in fiberglass mold making so I used that. You can think of SMC-compatible resin as a "primer" for ordinary filler, as long as there's a layer of SMC-compatible on the surface, ordinary filler will stick fine to that. You can apply SMC-compatible resin with a brush as a primer for the filler.

Good luck with your repair.

 

[woody367]

Thanks for all the help.