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Old 08-05-2007, 15:28   #1
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Fibreglass over plywood experiment

Polyester doesn't stick to wood very well. Epoxy does , but you can't put polyester over epoxy once it goes off. I tried putting polyester fibreglas over wet epoxy, before it kicked off and it stuck like **** to a balnket. When I tried to pry it off with a screwdriver, it could only be chipped off in pieces , some of which took a lot of wood with it and some of which broke up the fibreglass.
I used Industrial formulators G2 epoxy. It is best to experiment with it before using whatever epoxy you plan to use. Polyester is much cheaper and much easier to use than epoxy. A thin coat of epoxy is all it would take to get the bond, possibly S1 sealer, saving alot of time. The epoxy may take longer tyo go offf than the polyester, so I'd leave it a couiple of days before touching it.
In th elast 30 years the only way I have been able to get paints to stick to epoxy was top put the paint on while the epoxy is still wet. It seams that painting is not the only use for this tecnique.
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Old 08-05-2007, 19:26   #2
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Sorry! But!

I'd tend to disagree with most of what you have to say here. Polyester does stick to cured epoxy. Below is living proof. I've been working with the stuff for 30 years and for minor repairs and cosmetic jobs polyester works just fine over epoxy. I would never combine the two in a structural area without some major overlap. But I have yet had any delaminate from each other. Surface preparation is the key to any bonding.

And if you thin down polyester, just like epoxy, it will adhere to wood just as well.

I paint over epoxy all the time with great success. Again, it's surface preparation.

For the last four years this has been sitting out in the weather and it still will not come apart. It's polyester poured over cured epoxy.

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Old 08-05-2007, 21:08   #3
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Brent, I also have to disagree. Valspar VP 50 epoxy primer sealer is used extensively in the auto and industrial paint industry, and is painted over with polyurethane. I mention this product as it is the one I have the most experience with. I am sure there are other epoxy primer sealers that are used in the same manor. I used the same product on my trimaran, and used a single part poly topcoat. It has been on for about a year now on the hard with numerous washings, and other abuse that happens to a boat in process, and has shown no signs of failure.
I am curious why you want to use polyester instead of epoxy for your fiberglass. I have used epoxy for 100% of the glass work I have done on the trimaran, and am very happy with the end result.
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Old 09-05-2007, 00:59   #4
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Polyester is usually used in high build layups, often with very heavy wovens or most commonly, with the use of chopped strand gun application. Timber/Ply is usually used in area's of stiffening and forming. I do not know of any applications where Polyester is used to laminate over a ply surface, like you would Epoxy. Polyester does have poorer adhesion to ply than Epoxy does. To me, the saving is so minimal, why would you even consider scrimping in this area. Using Epoxy means you can have a far supperior bond and far supperior strength. Polyester also tends to shatter and crack easier than epoxy in any impact.
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Old 09-05-2007, 02:51   #5
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Instructions from EPIFANES (Polyurethane Topcoat Application):
Epifanes Polyurethane may be applied directly to clean degreased and sanded (to 320 grit) gelcoat, epoxy and surfaces previously painted with two part polyurethanes, but better results are usually obtained when two coats of Epifanes Epoxy Primer are used.

West Systems (epoxy) testing confirms that polyester gelcoats can be applied over cured WEST SYSTEM epoxy on repairs below the waterline.
EPOXYWORKS
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Old 09-05-2007, 13:24   #6
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Epoxy over ply

I can pull polyester fibreglass off plywood by hand very easily, no matter how much you thin it. Delamination of polyester from ply problems are very common.
Very high expense and difficulty of working with epoxy is a good reason to use polyester. Coatings to go between are another uneccessary expense, which paint companies love to sucker you into buying.
A friend was told by the experts to wait a couple of weeks before painting his epoxy coated hull with enamel. It fell off in sheets. He then followed my advice to paint it with epoxy again , then put the enamel on while the epoxy is still wet. That was over 20 years ago, and it hasn't come off since.
The amine blush of epoxy makes a good mold release. Sanding it off is a huge amount of work and that still doesn't give anywhere near the bond that wet on wet gives.
Puting other materials over wet epoxy takes zero surface preperation. The epoxy bonds extremely well to both the surface and the coating over it, saving a huge amount of labour, and expense.
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Old 09-05-2007, 19:19   #7
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No question wet on wet has some benefits, but it is still not the only solution. As for working with epoxy, I do not find it more difficult than Poly, personally.
Brent I respect your view here, but I disagree with it, and it is contrary to my personal experience. I would suggest anyone considering these two methods consider both options very carefully before deciding where to put their hard earned cash.
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Old 09-05-2007, 23:14   #8
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Quote:
Originally Posted by Louis Riel
I can pull polyester fibreglass off plywood by hand very easily, no matter how much you thin it. Delamination of polyester from ply problems are very common.
Very high expense and difficulty of working with epoxy is a good reason to use polyester. Coatings to go between are another uneccessary expense, which paint companies love to sucker you into buying.
A friend was told by the experts to wait a couple of weeks before painting his epoxy coated hull with enamel. It fell off in sheets. He then followed my advice to paint it with epoxy again , then put the enamel on while the epoxy is still wet. That was over 20 years ago, and it hasn't come off since.
The amine blush of epoxy makes a good mold release. Sanding it off is a huge amount of work and that still doesn't give anywhere near the bond that wet on wet gives.
Puting other materials over wet epoxy takes zero surface preperation. The epoxy bonds extremely well to both the surface and the coating over it, saving a huge amount of labour, and expense.
Brent
Yo Brent,

I agree with what you said. When restoring wooden yachts whose plywood decks or hulls have been glassed over using polyester resin, it is quite usual to remove the old fiberglass by hand as there is very little bond. A much better, much more durable (and more expensive) job can be done using WEST epoxy in place of polyester.

Regarding the superior "chemical" bond, it is true that many coatings typically used on boats will form an excellent bond if applied while the previous epoxy is still uncured. This seems especially true when applying bottom paint over an epoxied surface. Similarly, when additional "buildup" coats are required after laying glass, application before the previous material has cured saves a lot of surface prep. Once cured, the by-product of the resin/hardener must be washed off (soap and plenty of water works well) prior to sanding and applying the next coat, often an epoxy primer converter prior to LP topcats.

best, andy
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Old 09-05-2007, 23:29   #9
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Very high expense and difficulty of working with epoxy is a good reason to use polyester.
That I simply can not agree with. Epoxy is not that much more expensive, especially when considering the results of the job. Poly and Epoxy are chalk and cheese in almost all aspects. And thus should be considered as two very different processes. I don't know why on earth any one would want to laminate over ply with Polyester.
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A friend was told by the experts to wait a couple of weeks before painting his epoxy coated hull with enamel.
What expert?? A paint/coatings expert?? or some guy in the marina that thought he knew something. Because no expert would ever tell you that, unless closely followed by, if the epoxy is fully cured IT MUST, be keyed with a coarse paper first, and then the recomended primer/undercoat for the "system" should be used.
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which paint companies love to sucker you into buying.
Paint companies are not conspiracy agents. They formulate "systems". Follow the system and all the instructions, and the paint company can gaurenttee the product. Most all paint failures in the industry are because someone has not followed the instructions. It is very very rare that the product it'self ever fails.
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Old 10-05-2007, 14:37   #10
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Sanding a 40 ft hull to get a key is a huge amount of work and wasted energy when compared to painting wet on wet. I' ssuugest trying a test piece first , before doing a huge surface
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Old 10-05-2007, 22:25   #11
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Brent, that didn't answer anything.
But to your comment on sanding, yep, sanding Epoxy once fully cured is hard work. But you still have to sand cured epoxy before you put another fresh coat on anyway. So I don't get what you are on about.
When painting additional coats over epoxy base coats, you do not, nor ever should you put a coat of some other type of paint over wet epoxy. I am saying wet as in wet. Like as in, it is still tacky to touch. Epoxy paints still have solvents in them. If you do not allow the solvent to evaporate out correctly and you trap it in, you will have problems with any future coat. Especially if the next system uses a different solvent base. I have seen to the horror of the painter, several coats of a system applied and then two to three coats of the top coat applied. Everything looking sweet. Then the last coat applied and the entire thing starts reacting. It is devestating.
So would you please clarify what you mean by "wet".
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Old 11-05-2007, 02:01   #12
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Quote:
Originally Posted by Louis Riel
...The amine blush of epoxy makes a good mold release. Sanding it off is a huge amount of work and that still doesn't give anywhere near the bond that wet on wet gives ... Brent
You don't sand the blush - you wash it off (amine blush is water soluble), then abrade if recoating.
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Old 11-05-2007, 13:44   #13
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Thanks Gord. I missed that comment. Yes Amine blush is surface only. That is providing the epoxy was mixed in the correct ratio and then mixed thoroughly in the container and the ambient temp is within the correct range. Much of today's epoxies have formulations that result in little to no amine blush now. So that is no longer a major issue.
As I said above, you FOLLOW THE INSTRUCTIONS. Paint companies go to a lot of work testing there formulaes and give the advice for the best possible application. Remember, paint sales is about reputation. It's nice to have a beautiful gloss finish, but if it does'nt stay on or the gloss fades quickly or what ever, you are not going to buy that system again now are you. Plus, a seller of a product does not want to have to pay for a new job if the first one is proven to have gone wrong due to inferior product. Advertising for a paint company is right there in front of all of us everday, in vivid colours and finishes.
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Old 12-05-2007, 15:54   #14
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The only way I'v ebeen able to get anything to stick to epoxy tar is wet on wet, period.
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Old 12-05-2007, 16:01   #15
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Over the last 30 years having built or designed nearly 200 steel boats , I've seen people try a lot of different painting schemes. Absolutely nothing has been sucessful for getting paint to stick to epoxy tar, for the long haul,but wet on wet. Washing or sanding doesn't give anywhere near the bond.
Uneccessary sanding is for masochists.
My current paint job, 23 years old, was done that way and it's as good as the day I put it on.
No better way to make a fool of oneself than to proclaim that that which has been working well for decades" Won't work."
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