Thread: Who knows how to repair cracks in fiberglass?

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Yup, blew off the car all right.... Definitely gonna need some reinforcement (matt) on the inside to keep it together..... Make sure before you do any patching with resin and matt that you scuff the area thoroughly with 36 grit so you will get proper adhesion.....

Dave, what exactly do ya'll mean when you say "V out the crack"?

It's the same process for boats, look that up. When I do fiberglass repairs, I work with epoxy resins like those available from West System for many reasons. Epoxies bond to all other resisn, they are many times more flexible than polyester, and they are many times stronger. That way, you know the part will fail somewhere other than the repair.

If I were to do this repair, I would simply bevel the material back at least 8x the thickness of the top on both sides. Cut sheets of biaxial cloth to fill the bevel and prepare them to be stacked in the bevel. Less sanding is necessary if you start with the bottom sheet being the largest and reduce the size of each additional sheet. Work one side at a time so you can use gravity to your advantage. The great thing about West Systems is its versatility. Many fillers are available to make it do many things from glueing, filleting, to fairing. Use the low density filler to make a fairing compound like Bondo to reduce the amount of sanding and laminating you need to do. West Systems is available at West Marine and Boater's World. It costs about $45 for a quart of resin and a matching quanitity of hardener.

Grind out the edges of the cracks into a V-Pattern, this will allow more resin into the crack plus you will be able to work some of the shredded matt into the V giving increased strength in the cracked area...

That should be able to be repaired. Grind the inside with 24grit disc and apply resin and 1 piece of 1.5 oz. mat to the entire inside of the panel, push out the air and let dry grind again and apply second piece to the inside. This will give the panel back its strength and allow you to work on the outside with out the cracking continuing. V out each crack and follow Daves instructions. Make sure you push out the air when appling the mat and resin.

if you do not post cure it i think it on a black car your repair will shrink and air cure will move in the heat of the sun any thing poly or epoxies will move more then the MSC this stuff is thremal set in the long run it may be a much bettter finding a used lid . the west systems are good and made here in bay city BUT the msc is not made by west systems from what i have seen it work great on alot of stuff but not to sure i would use it on msc ?? boats are not made out of msc . msc is a different animal .but i know what works on the stuff .i work on trucks an have put many of them back to gether with fiber gell and mat in side out would be the way to fix it

Thanks for all of the help.
Zak

Here's a link, the third drawing shows the 'V' prior to rebuilding the material.

Fiberglass Repair by Don Casey

Oh, ok. Thanks.

West Systems also has a lot of how-to stuff on their website. There is a lot of discussion about whether or not to lay the biggest piece of fiberglass in first or the smallest when you are filling the bevel. Either way produces an acceptable repair, but from my experience if you start with the biggest piece, there is less sanding to be done when you are finished. There is also less of a chance of getting unreinfoced pockets of resin. Oh, don't forget to buy a resin roller.

Oh, ok. I'm going to go ahead and finish sanding it down, then I'll get back to you guys from there.

Another question...do I need to sand the whole thing down to the fiberglass, or just in the repair spots?

West systems is good, i have used it a lot. One thing, You cant use matt with epoxy, use only cloth.. The glue that holds the glass fibers together in the matt, needs the polyester resin to disolve it. Epoxy wont do it.

epoxy sticks to polyester, but polyester does not stick to epoxy.

I love glass work, but it makes me itch.

Jim

You can use most matt with epoxy. The epoxy won't dissolve the binder which makes it harder to wet out, but you can still use matt and it still works fine. I did suggest biaxial cloth for this reason, though.

Here is a fiberglass repair I did. I replaced a section of a boat stringer. I used 2 layers of 1.5 oz mat and 1 24 oz roven. I used West System epoxy and it wet the mat out just fine. In fact, you can still see the wood underneath all of the glass.

Originally Posted by 76GMC1500

You can use most matt with epoxy. The epoxy won't dissolve the binder which makes it harder to wet out, but you can still use matt and it still works fine. I did suggest biaxial cloth for this reason, though.

Here is a fiberglass repair I did. I replaced a section of a boat stringer. I used 2 layers of 1.5 oz mat and 1 24 oz roven. I used West System epoxy and it wet the mat out just fine. In fact, you can still see the wood underneath all of the glass.

Just looking at that picture, I smelled the west system. I havent used it in a few years. Good point on the mat. I have done it but didnt think it was ok.

Jim