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Fiberglass Repair (Resin Preference Poll)

Preferred Resin.

  • Epoxy

    Votes: 13 86.7%
  • Polly

    Votes: 1 6.7%
  • Vinlyester

    Votes: 1 6.7%
  • Other?

    Votes: 0 0.0%

  • Total voters
    15

Thursty30

Member II
I spent all day watching these videos, he breaks it down pretty well and I was feeling a lot more confident tackling some of the carpentry projects, namely patching the holes left after relocating/eliminating some of the thru hulls. Operative word = was, until I typed Epoxy vs Poly into google. I am sure the process he's shown is similar with either resin, but I'm interested in some objective input on how far poly is behind epoxy in terms of strength and if you would feel comfortable doing a repair of this nature below the waterline with it.

Thanks in advance.

Videos referenced above: https://youtu.be/i9hfpOCnzEs
 
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Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Given the superior adhesion of epoxy to any existing polyester laminate, I would always advise epoxy for a patch.
Taper the edge of the opening that you are filling in -- about a 12 to 1 slope if I recall the West System instructions.

Be sure your are bonding to a clean and sanded/abraided surface.

I have been using West System products for several decades. I like their whole product universe of resins, hardeners, pumps, thickeners, etc.
I know a major boatyard here that uses West System epoxies for all repairs and modifications, FWIW.

Loren
 

bigd14

Contributing Partner
Blogs Author
Epoxy, yes. Easy to work with, and doesn't stink. West is great, and easy to find, but expensive. I have used Raka almost exclusively, with excellent results.

Here is my procedure for thru hull patches.

1. Clean bottom paint off with solvent, or sand off.
2. Sand around thru hull approximately 8 inches thru gelcoat to fiberglass with heavy grit (40-60). Avoid contamination with bottom paint.
3. Feather the edges of the hole on the outside back about 4-6 inches. I don't like to get a razor thin edge.
4. Clean the heck out of the inside of the boat. I use degreaser, followed by acetone scrubbed around with a heavy brush, followed by Interlux 202 fiberglass solvent wash (202 is nasty, use a respirator!)
5. Sand a large area on the inside of the boat (about a foot square) around the thru hull. Very little taper on the inside.
6. Glass in an oversized patch of 1708 biaxial mat to the inside of the boat, to ensure lots of bonding surface. That layer is your last line of defense if something goes wrong with the outer layers.
7. Wait a few hours for the inside layer to start firming up.
8. Install the outer patches of 1708 biax. I use one small patch the same size as the hole first, then follow with the larger to smaller patches (as West recommends).
9. Sand and fair the outside.
10. Use the gray barrier coat epoxy additive to paint a couple coats over the patch and any exposed gelcoat.
11. Bottom paint patch.

Good luck with your project.
 

Bob Hunt

Junior Member
The Lenox method for fiberglass repair...

Dave and Mark Lenox have used the following basic components since 1985:

1. Interplastics CoREZYN VE8117 vinylester resin

2. Hi-Point 90 methyl-ethyl-ketone-peroxide (MEKP) catalyst

3. Cab-O-Sil TS-720

4. Cook's sanding polyester gelcoat (NPG ISO)
 

Thursty30

Member II
Epoxy, yes. Easy to work with, and doesn't stink. West is great, and easy to find, but expensive. I have used Raka almost exclusively, with excellent results.

Here is my procedure for thru hull patches.

1. Clean bottom paint off with solvent, or sand off.
2. Sand around thru hull approximately 8 inches thru gelcoat to fiberglass with heavy grit (40-60). Avoid contamination with bottom paint.
3. Feather the edges of the hole on the outside back about 4-6 inches. I don't like to get a razor thin edge.
4. Clean the heck out of the inside of the boat. I use degreaser, followed by acetone scrubbed around with a heavy brush, followed by Interlux 202 fiberglass solvent wash (202 is nasty, use a respirator!)
5. Sand a large area on the inside of the boat (about a foot square) around the thru hull. Very little taper on the inside.
6. Glass in an oversized patch of 1708 biaxial mat to the inside of the boat, to ensure lots of bonding surface. That layer is your last line of defense if something goes wrong with the outer layers.
7. Wait a few hours for the inside layer to start firming up.
8. Install the outer patches of 1708 biax. I use one small patch the same size as the hole first, then follow with the larger to smaller patches (as West recommends).
9. Sand and fair the outside.
10. Use the gray barrier coat epoxy additive to paint a couple coats over the patch and any exposed gelcoat.
11. Bottom paint patch.

Good luck with your project.

Thanks for the detailed response, I like the idea of a layer of 1708 to back up the patch, as opposed to the temporary backer recommended by west. When working with the epoxy resin, as long as I pay attention to pot life, do I have to wet every layer of the patch and then apply as one piece? or can I lay it into the hole one layer at a time, wetting as I go?

Afterthought: I am going to have the yard sand for a new barrier coat and couple layers of CSC before I launch. I guess it would make sense to wait until they complete that so I don't even have to think about any bottom paint contamination.
 
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bigd14

Contributing Partner
Blogs Author
I spread the epoxy out in a paint roller tray and then don't have to worry about pot life. And I use slow hardener unless its the middle of winter. I always wet all layers of the biax in the roller tray before applying, That way there are no dry spots. 1708 biax is hard to wet out, especially if it is below 70 degrees and the epoxy is sluggish. For larger pieces I will put it in the tray, pour epoxy over it and massage the epoxy in. This does not work for the smaller pieces they just fall apart. A small chip brush works well to push epoxy into the biax and to remove air bubbles (repeatedly jam the tip of the brush lightly into the fiberglass to remove air bubbles)

Also, I neglected to mention two items, the first being vacuum and then clean the sanded area inside the boat with acetone before glassing to remove all dust, and the second is to water wash the freshly cured epoxy before sanding and painting the barrier coat on. This is to remove amine blush that appears as the epoxy cures.
 

u079721

Contributing Partner
One of the benefits of boating in the Saginaw Bay area of Michigan was that Gougeon Brothers (makers of West System epoxy products) was located there. Every year or so they offered a "Glue U" class through one of the local community colleges on fiberglass boat repair. It was a fantastic opportunity to not only learn from the experts, but you could also ask their advice on the best way to accomplish particular projects.
 
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Bob Hunt

Junior Member
Cab-O-Sil TS-720...

Cabot Corporation
Cab-O-Sil Division

"CAB-O-SIL TS-720 Treated Fumed Silica in Vinyl Ester Resins

This technical data sheet describes the use of CAB-O-SIL TS-720 treated fumed silica as a thixotropy for vinyl ester resins. This high purity silica is treated with a diethyl silicone fluid. The treatment replaces many of the surface hydroxyl groups on the fumed silica with a polydimethyl siloxane polymer. The treatment makes the silica extremely hydrophobic."

The Lenox method adds TS-720 to both COREZYN VE8117 and Cook's gelcoat to increase the hydrophobic property of the laminate.

Bob Hunt
 
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