Epoxy vs Vinylester

McReef · #1 03-03-2011, 10:26 AM

In a critical structural application does epoxy hold a clear edge in the category of adhesion?

The application - Construction of an integral bracket which will tie into the existing transom, stringers, and interior hull surfaces.

Let us stipulate for the sake of argument that the resins are properly prepared, the fabric being used is appropriate for the job, the existing structure is fully cured and sound (polyester), and adequate and correct prep work is done prior to application.

dbiscayne · #2 03-03-2011, 12:07 PM

I'd vote for epoxy, have used both and it always seems that the accidental drops of epoxy are stuck to whatever they land on better than vinylester, ie you can usually chip a stray drop of vinyester off & it'll come off cleanly, not so with epoxy it usually takes a layer of whatever it landed on with it.
Lots of good scientific data on the web that back up epoxy when fixing or adding to an existing cured structure.

KenB · #3 03-03-2011, 12:16 PM

I am interested to hear what others say.

My impression was that you can can poly on top of poly, or epoxy on top of poly, but you cannot add poly on top of epoxy (no chemical bond).

I use the basic no blush epoxy from the new hampshire guy with the crazy website, but have been thinking about using poly or vinylester.

Blue_Heron · #4 03-03-2011, 01:47 PM

Quote:

...not so with epoxy it usually takes a layer of whatever it landed on with it.

I haven't used vinyl ester, but I have used epoxy so I'll add to the anecdotal data. I forgot to clean up a ribbed aluminum roller after an epoxy layup and found it stuck to the deck the next day. When I pulled it off, it took a neat chunk of the gelcoat with it. So the epoxy's secondary bond was stronger than the gelcoat's (presumably) primary bond.

I've been buying my epoxy from US Composites. Their epoxy is at about the same cost as their vinyl ester @ $45/gallon, so for me it's a no-brainer.

Dave

shine · #5 03-03-2011, 02:18 PM

for secondary bonding, there is no compsrision. Epoxy is far superior in secondary bonds.

McReef · #6 03-03-2011, 04:03 PM

Quote:

My impression was that you can can poly on top of poly, or epoxy on top of poly, but you cannot add poly on top of epoxy (no chemical bond).

I think you are on track there. From what I can gather, while epoxy will cure just fine over poly (and bond aggressively), the chemical makeup of epoxy actually inhibits the curing process of poly and vinyl resins. The lack of bond is due to the fact that the newly applied poly/vinyl resin never fully and properly cures at the interface of the two materials.

McReef · #7 03-03-2011, 04:25 PM

Quote:

I've been buying my epoxy from US Composites. Their epoxy is at about the same cost as their vinyl ester @ $45/gallon, so for me it's a no-brainer.

I had noticed they seemed to be much cheaper than some of their competitors, but wondered if it was because they were selling a significantly inferior product. You've had good luck with it?

KenB · #8 03-03-2011, 04:34 PM

I got basic no blush epoxy from Progressive Epoxy in NH. With the ... dense website. Lack of marketing results in lower prices... for a superior product. Unlike west, there is no amine blush or wax removing step.

Another question: faring compound. Use the pre-mixed stuff (quick fair) or make your own?

newellchunker · #9 03-03-2011, 07:22 PM

Quote:

I had noticed they seemed to be much cheaper than some of their competitors, but wondered if it was because they were selling a significantly inferior product. You've had good luck with it?

I've used US Composites on a hard-top restoration and I'm now using it in a transom re-core and have had NO issues with it. As far as I'm concerned its a very good product and competitively priced!

Blue_Heron · #10 03-03-2011, 08:39 PM

Quote:

I had noticed they seemed to be much cheaper than some of their competitors, but wondered if it was because they were selling a significantly inferior product. You've had good luck with it?

Good products. Good prices. The only things I can get cheaper locally are polyester resin and glass cloth. And that's because they are both basically commodities and the cost difference is the added shipping.
Dave