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Old 08-09-2013, 11:36   #1
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Cracked fiberglass hding tank

We have an integral fiberglass holding tank where the top area surrounding the access port experienced a large delaminating crack/ separation of material caused by internal pressure. Is this fixable with epoxy sealing or does it need to be grinded and glassed? Concerned with grinding given access issues and large area. When pressure subsided separated glass fit back into place.
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Old 08-09-2013, 11:38   #2
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Re: Cracked fiberglass hding tank

frozen tank or hard grounding?
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Old 08-09-2013, 11:49   #3
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Internal pressure from clogged air vent and electric flush pump. Similar to freezing I suppose.
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Old 08-09-2013, 12:31   #4
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Re: Cracked fiberglass hding tank

I had to repair mine a few years ago. I sanded with 80 grit, epoxied the edges, then reinforced with glass cloth and glass tape. It was a little unpleasant sanding but not really too bad. Of course I waited until completely dry. you might get by with just epoxying the delamination, but you should contemplate would it be strong enough if the event happens again.
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Old 08-09-2013, 12:38   #5
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That is pretty much exactly what I was thinking. Did you use west system epoxy? If so, which number. Thanks for the input
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Old 08-09-2013, 12:41   #6
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Re: Cracked fiberglass hding tank

It will most definetly crack again if you just seal it with epoxy. You must also use glass. You can buy 3 -4" wide glass tape that should do it.
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Old 08-09-2013, 12:46   #7
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Re: Cracked fiberglass hding tank

believe it or not, you can use JB weld. sand the area, coat liberally. i used it on powerboat manifolds.
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Old 08-09-2013, 12:50   #8
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Re: Cracked fiberglass hding tank

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believe it or not, you can use JB weld. sand the area, coat liberally. i used it on powerboat manifolds.
I am a big fan of JB, I sealed a cracked exhaust manifold with it 15 years ago and its still holding. However, it will not work in theis application. The OP said integral FRP tank. This tank will flex, expand and contract with temperature and pressure. Think of plastering a dry wall joint in a house without using drywall tape .... it just won't last.
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Old 08-09-2013, 13:06   #9
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Re: Cracked fiberglass hding tank

I used West, because I had it, and probably used 206 hardener. I also use MAS epoxy, which has no odor and seems to be a good product. Mine split at the bottom, and if I remember correctly, I used fg tape on the inside and cloth on the outside. I did coat it after just laminating the cloth and tape to try to make a reasonably smooth surface to keep all the wonderful stuff from getting caught on rough edges. In my opinion, dry is much more important than sterile. A little staining didn't stop adhesion, and just recently I over stuffed it and my repair held.
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Old 08-09-2013, 13:07   #10
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Ok, so we are thinking west system 105 epoxy resin to fill , bond and secure the crack. Then light 80 grit sand and 3 layers of full fiberglass application. Does this sound correct?
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Old 08-09-2013, 13:09   #11
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Re: Cracked fiberglass hding tank

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Ok, so we are thinking west system 105 epoxy resin to fill , bond and secure the crack. Then light 80 grit sand and 3 layers of full fiberglass application. Does this sound correct?
Sounds good, Don't forget to clean the surface with acetone after sanding.
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Old 08-09-2013, 13:29   #12
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Re: Cracked fiberglass hding tank

That should work, but I would be careful with the acetone wipes. On some boat building forums, some have had bonding issues after using acetone. What is more appropriate, is to wash the cured resin with fresh water and a scotchbrite pad to remove "amine blush" which occurs with some epoxies, then sand.Don't just sand without cleaning, the blush gets driven into the epoxy. The blush can cause a lack of bonding. The MAS epoxy is a none blushing epoxy when you use their slow hardener. In all honesty, I haven't used MAS for any glass repair work, but have built a couple of wood kayaks that are glass covered, and have been very happy with the product. Because that is what I have in my shop now, I would use it for a glass repair, if I had to do one.

I would get glass on both sides if at all possible. Three layers would be good, one on each side would probably work also. While you are up to you elbows in epoxy, more could be better. Also, you don't have to do all layers at once, if it becomes difficult to deal with it. I have read somewhere, that one of the epoxy companies did testing, and found no real difference between all layers at one time or one at a time. Actually, I think they found one at a time was better, because it was easier to control resin to glass ratio. The real strength is in the glass, not the epoxy.
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