How to fix stress crack in fiberglass under seat cushion

[ratdude747]

While replacing some bungee cords on my bow riding seats, I found a stress crack in the seat opening:



Specifically the crack radiating from the hull edge (the other is just in the Gel coat AFAIK). It goes all the way through the wood and inner glass.

How should I mitigate this? Not looking for a cosmetic repair (as it's hidden under a seat cushion), but I also don't want the damage to continue as that's my wife's favorite seat. Preferably a repair I could knock out over an evening. Marine-tex? JB Weld?

 

[Chris1956]

You need to grind out the cracked glass and reglass it. The best repair would be on both sides, however, it looks like grinding the inside of the cracked glass will be difficult.

Can you reinforce the inside with a piece of plywood?

 

[ratdude747]

Would a bead of JB weld on the bottom of the crack area suffice as a temporary fix at least?

The only grinding tools I have at home are an angle grinder and an oscillatory saw, neither of which feels like the right tool. A die grinder with a carbide burr would be ideal but that's not something I have at the moment.

 

[Scott Danforth]

Would a bead of JB weld on the bottom of the crack area suffice as a temporary fix at least?

No

only way to get the stress cracks to stop is to grind down and build back up

 

[ratdude747]

No

only way to get the stress cracks to stop is to grind down and build back up

What if I cut the worst of it out with the saw (the split wood only goes to the edge of the rim), drilled the end of the cut, feathered/beveled the split, then JB welded that?



(Red cut and drill, yellow is feather/bevel area).

Trying to see if there is anything I can do with current tooling/time that would at all help. If not, then it is what is and I'll plan on tooling up for a bigger repair at the end of the season. Other than supporting the weight of somebody sitting, it's not structural...

Edit: I'm not looking to restore the aesthetics here... just trying to keep the split from spreading out from under the seat and eventually ruining the hull.

 

[Chris1956]

The FG cracked because it was not strong enough. FG cloth provides the most strength of the hull. Epoxy putty like JB weld is strong in compression, but not laterally like cloth is. You can embed cloth in the JBWeld, and add some strength, but not enough, IMO.

Grind out the bad glass, and taper the area. Fill with multiple layers of cloth, with the first layer being a small piece of cloth, followed by larger pieces of cloth. Lay all the cloth with one batch of resin. Now it is as strong as the original, but not strong enough as the original cracked.

Now grind the backside of the crack and repeat the process, using cloth to build up the thickness more than the original.

If you cannot get to the backside, sand it well, cut a piece of 1/2 plywood and use heavy layers of glass to attach it on the backside of the crack. A couple of stainless steel wood screws can hold the plywood in place until it cures.

 

[froggy1150]

Just so you have an idea.... that repair should go 6-8" each way,min, 3-5 layers, top and bottom. And as deep as you can get.

 

[cyclops222]

Why does it look like a heavy impact crack ? There is even a 2nd crack to the left of the picture.