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pcford
10-04-2007, 08:07 PM
Vinylester-Epoxy

Anybody know if vinylester sticks to epoxy?

Thanks in advance.

Todd Bradshaw
10-04-2007, 09:44 PM
Probably not well enough to bet on.

pcford
10-04-2007, 09:50 PM
Ok, thanks Todd. As I thought...thanks.

peter osberg
10-04-2007, 09:56 PM
epoxy bonds fabric quite well to polyester fabric that has had a vinylizing paint (mek based) layer applied, but that may not be what you are asking.
peter

Todd Bradshaw
10-04-2007, 10:19 PM
I haven't tried it, but had friends in the canoe business who tried various combinations:
Epoxy skin coats in the mold with a very light layer of cloth to eliminate the excess weight of gelcoat because the epoxy wouldn't shrink or get pin holes as it cured and then a buildup of vinylester or polyester for the remainder of the layup to keep costs down. Another was epoxy laminate built up over standard gelcoat. They had a lot of delamination problems between the layers on most of these hybrid layups and eventually abandoned the whole idea. I don't know enough about the chemistry to know whether they were getting any kind of chemical bond at all, but when both substances were freshly applied in rapid succession (like production building) they didn't seem to get along very well. The "esters" also often have very different hardness, flex and long-term shrinkage rates than most epoxy. Perhaps there are some new formulas which might work better, but I haven't seen them.

pcford
10-04-2007, 10:47 PM
To define the situation better:

We are preparing to 'glass a hull which has epoxy fairing compound on it. A guy showed up with vinylester which which to do the 'glassing. He was told by a designer that that is what he specifies on his boats. I believe the designer did not understand that the epoxy had already been laid down.

I know that epoxy stick to polyester, but polyester does not to epoxy. I know nuthin' about vinylester except that I think it is supposed to be better than polyester. Stinks the same though.

George Roberts
10-05-2007, 12:10 AM
pcford ---

A simple google search should answer your question. I know one dealer of epoxy and vinylester has the answer in his literature but ...

Due to age I no longer can remember either the dealer or the answer.

Todd Bradshaw
10-05-2007, 12:50 AM
I found a bunch of typical discussion board stuff, but not much from official sources. Then I got lucky and found this post from one of the Gougeon tech guys in reference to using gelcoat over WEST epoxy. I would assume that coating with resin, rather than gelcoat, would be same basic story, just without all the pigment and filler contained in most polyester or vinylester gelcoat.

"This is a question we get quite often. There is a common misconception, fueled by some gelcoat manufacturers and by some expensive failures in the field, that gelcoat will not bond to epoxy. Given that polyester resin bonds poorly in a secondary (mechanical) bonding situation which consequently makes epoxy resin the resin of choice for repairs. How can one be squared with the other?

The answer is surprisingly simple - gelcoat does bond to a properly cured and prepared epoxy surface. There are a couple issues to be aware of to have success making this repair. There are three situations that cause gelcoat to not cure over epoxy all related to the hardener chemistry. Epoxy hardeners are basically a blend of amines and amines can terminate the chain reaction formation of the radical molecule that is the basis of polyester (and vinylester)
cure chemistry. So by carefully mixing, curing, and preparing of the epoxy so that there are no unreacted amines to interfere with the gelcoat cure, gelcoat bonds quite well to epoxy.

The first situation is undercured epoxy. Gelcoat applied to undercured epoxy will be in contact with unreacted amines and the cure will be halted.
The second situation is if the epoxy is mixed off ratio so that it is hardener rich, again leaving unreacted amines free to interfere. Third is the issue of amine blush, commonly called blush. Blush is a surface phenomena that is a reaction of the amine molecules at the surface with the carbon dioxide in the air. It forms easiest in the presence of moisture, so working in cool, humid environments will maximize the formation of blush. Any amine hardener has the potential to blush, but it can be minimized by careful choices of amines in the formulation. In fact, WEST SYSTEM 207 Special coating hardener is one of the lowest blushing hardeners on the market and still maintains structural properties on par with our other hardeners. Regardless of chemistry blush is very easily dealt with because it is water soluble. A simple wash with clear water removes the blush. No soap, no solvents. Then sand that washed surface with 80 grit paper to provide the gelcoat with sufficient key so it won't run. Be sure to use non-air inhibited gelcoat that has a paraffin wax added. Gelcoat is applied over epoxy on a routine basis everyday in boatyards that are aware of these issues.

You can find further reading on the subject on our web site <www.westsystem.com> on the 'Epoxyworks Magazine' tab, back issues, #22. The article covers gelcoat over epoxy below the waterline. (yes, it is done!!)"


This might also explain some of the issues I saw on the discussion boards like a layer of goo forming between the two resins, so it may be more of a preperation issue than anything else. The information above would pretty well explain why my friends' attempts to switch resins during a hand layup procedure over partially cured layers of epoxy went bust. T.E.B.

Bill Lowe
10-05-2007, 01:01 AM
System 3 has a epoxy blend that accepts gel coat within a specifin time window. Its called Surfboard Resin or SB and numbers check there web site. I have used it a few times sucessfuly.

pcford
10-05-2007, 09:31 AM
Thanks, Bill and others. George Roberts...I have done a Google search with inconclusive results.

To review, a boat has to be covered with 'glass. The boat has epoxy fairing compound on it. Others involved in the restoration, included a noted designer have suggested vinylester. I do not know if the designer understood that the fairing compound was epoxy. There are certain areas of the boat that are vital to be protected. The boat will be subjected to extreme stress in these areas.

I have to have nearly 100 percent certainty that there will not be an adhesion problem with the vinylester/'glass over any areas which contain epoxy.

pcford
10-05-2007, 12:57 PM
Talked to Kern at System 3....there are problems with adhesion. We are going with epoxy.