Polyester / Vinylester over Epoxy?

[Capt. Chris]

We are at the deck stage on our 28 Topaz project, the deck is biax /epoxy over balsa core and want to know if once the faring is done , can it be top coated with poly or even better , vinylester gelcoat. I've heard different comments on this subject and don't want to get too far without some input from the pros!
Thanks in advance, Chris

 

[rxcomposite]

Poly over Epoxy

Never. One is base and the other acid. It will delaminate after a period of time. I have tried it.

Rx

 

[jimslade]

polyester will not stick to epoxy but vinylester will. vinyl is similar to polyester. polyester is small chain carbon whereas vinylester is long chain carbon which makes it more flexible. epoxy's base is amine which is a different family altogether. you can put epoxy over polyester but not the other way.

 

[JR-Shine]

yep, it wont stick. Even if it did, paint is better than gel coat.

 

[D'ARTOIS]

No! Rxcomposite is right - never epoxy over ....esters. After a certain period adhesion is lost.

 

[Capt. Chris]

Does Ester have a sister?

Anyway... I'm getting a little nervous. We made tons of repairs and modifications to this hull with epoxy. Does this mean the repairs will start delaminating? The deck is easy enough to paint, we thought we would use the non-skid mat from mold-craft to get a uniform textured surface instead of the shaker method.
Thanks Chris

 

[D'ARTOIS]

It is as it has been said. Epoxy over ....esters, YES!
.......estres over EPOXY, NO!!!

 

[Capt. Chris]

Since we're on the subject, has anyone used Durotec vinylester fairing primer over epoxy on the hull for the final fairing? This was our plan since it can be laid on heavy and is very easy to sand . Any suggestions?

Thanks , Chris

 

[rxcomposite]

Paint over epoxy

Capt Chris,

It has been said that epoxy will adhere to almost anything but im not so sure anymore. Epoxy is just a better resin but i just don't mix materials anymore.

Talk to a paint shop or to a paint representative. Especially those that finishes cars. They are very knowledgeable on this matter if it will make you feel better. There is also a lot of articles on painting cars, even fiberglass ones that deals with the paint, primers, ect.

Boat supply store gives free handouts on painting/topcoating boats. Leaflets are one sided, they work only for the product they promote but will be informative as well.

I once primered a boat with epoxy thinking that i would have a good grip over poly. When the paint guys came over, they asked me to scrape it off as it is not compatible with the paint they are going to use. They wont guarantee the job.

Rx

 

[rxcomposite]

mixed up?

D'Artois,

Thanks D'Artois. But i think you got your bottles mixed up in your last post.

Cheers,
Rx

 

[rxcomposite]

Why Ester will not Stick

I did some research on the polymers (uncured resins) to find out the reason on adhesion between different resins.

General Classifications of Resins
Ester Group
Ortho Resin
Isopthalic Resin
Vynil Ester Resin

Epoxy Group
Bisphenol
Phenolic- Dow Den
Hydroxyphenil- Shell Epon
Dianiline- Ciba

These polymer crosslinking or hardening takes place by the addition of a curing agent. The crosslinking reaction is quite different from each other.

*Esters are held in suspension by a crosslinking agent (monomer) until an initiator (peroxide) is added to start the carbon-carbon chain reaction. The chain reaction produces water as a byproduct. Although newer resin compound eliminates water byproduct, the degree of polymerization is not so dense.

*Epoxy crosslink within the epoxy group by the addition of a curing agent (hardener). Polymerization is much dense which accounts for the good “grip” or adhesion to the surface of the “substrate” material.

Esters, therefore, will not provide a good grip on the “substrate” material as epoxy does.

There are many formulations of primer/paint/topcoat that will “grip” the “ester” family but only a few that will be compatible with the “epoxy” group except perhaps epoxy itself. That is why epoxy boats are harder to paint.

By my own mistake, I have added epoxy (primer) to the boat limiting myself to the type of paint that can be used.

Other interesting subject.

Marine Composites- Eric Green and Associates 1990
1.“Vynilester, having excellent physical properties, can provide excellent permeation barrier to resist blistering when used as an outer (wet) layer 20 to 60 mils thick” (the inner side is the “dry” side). I will assume that subsequent layer of Iso or Ortho resin can be applied over it and it will stick because it belongs to the same family group.

2. “Initiator compounds are sometimes erroneously called catalyst. It is not a true catalyst as it is consumed in the reaction” Fundamentals of Composite Manufacturing- Dr. A. Brent Strong 1989.
“ The material we commonly called catalyst (MEKP)is actually not a catalyst. It is an initiator.”- Composite Fabrication – Scott M. Lewit- Vol 18, #9, P 100.

 

[FAST FRED]

To sum it up , Epoxy is an excelent GLUE that will stick to most everything , but not very much besides Epoxy will actually stick to epoxy.

I would scuff the surface and use ONLY epoxy fairing compound .

FAST FRED