| |  Re: Fiberglass Gelcoat Repair on Hull Bottoms
[Re: Tornado]
#37900
09/20/04 03:11 PM 09/20/04 03:11 PM |
Joined: Jun 2001
Posts: 12,310
South Carolina Jake 
Carpal Tunnel
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Carpal Tunnel
Joined: Jun 2001
Posts: 12,310
South Carolina | From what I found, in general, you do not want to use a Polyester resin over cured epoxy because it will not bond well. However, epoxy will bond well to polyester and because of this it's safe to use epoxy to make repairs on most fiberglass substrates. This information is on the West System site - there's a lot of usefull stuff there.
Jake Kohl
| | | Re: Fiberglass Gelcoat Repair on Hull Bottoms
[Re: Jake]
#37901
09/20/04 04:34 PM 09/20/04 04:34 PM |
Joined: Jul 2001
Posts: 1,200
Vancouver, BC Tornado
veteran
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veteran
Joined: Jul 2001
Posts: 1,200
Vancouver, BC | This makes sense...but why is polyester-based gelcoat used on my epoxy boat? This is how it comes from the factory. Is it put on prior to full epoxy cure? Mike. From what I found, in general, you do not want to use a Polyester resin over cured epoxy because it will not bond well. However, epoxy will bond well to polyester and because of this it's safe to use epoxy to make repairs on most fiberglass substrates. This information is on the West System site - there's a lot of usefull stuff there.
Mike Dobbs
Tornado CAN 99 "Full Tilt"
| | | Re: Fiberglass Gelcoat Repair on Hull Bottoms
[Re: Tornado]
#37902
09/20/04 10:19 PM 09/20/04 10:19 PM |
Joined: Jun 2001
Posts: 12,310
South Carolina Jake
Carpal Tunnel
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Carpal Tunnel
Joined: Jun 2001
Posts: 12,310
South Carolina | I found this at the West System site http://www.epoxyworks.com/22/polyester.html There is a wealth of information (granted...it's probably a bit biased) at http://www.epoxyworks.com/ See the last few articles listed on the left for some great explanations. Understanding the materials
Polyester resin laminates achieve their highest strength when the bonds between layers of fiberglass are chemical or primary bonds as opposed to mechanical or secondary bonds. The manufacturing process for polyester boats has been developed so that a chemical bond exists between the gelcoat and the laminate. When a polyester boat is built, polyester gelcoat is first sprayed onto the mold surface. The first layer of the laminate is then applied to gelcoat, which has not completely cured. The two layers eventually cure together with a chemical bond between them.
Applying gelcoat to a cured laminate relies on a mechanical bond. Because of the difference in curing chemistry, it is not possible to achieve a chemical bond between epoxy and polyester gelcoat. We developed some tests, to determine whether or not the mechanical bonds achieved between gelcoat and properly prepared, cured epoxy were strong enough to achieve a durable repair... the test information shown on the site indicates only a slight reduction in bond strength between epoxy and and a polyester gel coat and they were really focused on boats that were left in the water (the rumour was that because the gel coat will absorb water and the epoxy will not, that the bond will suffer).
Last edited by Jake; 09/20/04 10:27 PM.
Jake Kohl
| | | Re: Fiberglass Gelcoat Repair on Hull Bottoms
[Re: carlbohannon]
#37904
09/21/04 09:49 AM 09/21/04 09:49 AM |
Joined: Jun 2001
Posts: 833
St. Louis, MO, Mike Hill
old hand
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old hand
Joined: Jun 2001
Posts: 833
St. Louis, MO, | I see a lot of people use epoxy but I don't see why. I think polyester sticks best to polyester. Plus polyester is a ton cheaper. I think polyester is easy to work with also. If I were to be working with preexisting epoxy then I would stick with epoxy.
Mike Hill
Mike Hill
N20 #1005
| | | Re: Fiberglass Gelcoat Repair on Hull Bottoms
[Re: carlbohannon]
#37905
09/21/04 02:21 PM 09/21/04 02:21 PM |
Joined: Jul 2001
Posts: 1,200
Vancouver, BC Tornado
veteran
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veteran
Joined: Jul 2001
Posts: 1,200
Vancouver, BC | Thanks Carl, didn't know this was how the boats came from the factory. My boat was originally a light pink color (this from the original owner and also from some scratches on the deck). The second owner had it re-painted to the off-white/grey, I believe with Imron, just prior to selling to me. anyway, I think my gelcoat repair on the epoxy filled puncture/scratch will hold up...it's certainly stuck well and I don't keep the boat in the water, which is sounding like the main reason this issue is of concern. Mike. Mike
Your Tornado is a Marstrom? Marstroms come from the factory painted with Spies Hecker auto paint. The cloest US equivilent is IMRON pure white base. A good auto paint shop can make up some 1 part touchup paint for you.
If you will do a search, you will find a thread on this from a couple of years ago.
I can't imagine anyone coating an expoxy boat with gelcoat. You would have to prime it to get it to stick
Mike Dobbs
Tornado CAN 99 "Full Tilt"
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