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  #1  
Old 05-16-2007
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Resin Compatibility

For some reason, I am still confused about the different types of resins. Specifically, I'm wondering what is the difference between Expoy, Polyester, and Vinylester resins. Will any one of these bond to any other?
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Old 05-16-2007
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Crickets chirping...
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Old 05-16-2007
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Uhmm - the difference is what they are made of. In a nutshell. Polyester resin is the most commonly ued resin. It is the material that most hulls were/are made of. It is not as strong as epoxy, and it is less waterproof than vinylester. It weighs less than epoxy, as it is less dense.

Polyester resin has very noxious fumes and generates a LOT of heat when it sets or "goes off". The primary reason that you would use it would be if you were doing a large repair on a polyester hull, and wanted to use a material with similar strength/flex/weight so as not to exert undue stress on the original part of the hull, and to avoid excessive weight.

Vinylester is a version of polyester with - you guessed it - vinyl added to it to increase it's resistance tp water penetratioin. You will commonly find it used as an outer layer on hulls that were built after the mid to late seventies. It is still used to day. Same working characteristics as polyester.

Epoxy is the strongest material and is the stuff that is most commonly used by amateurs for building/repair. It is strong, does not generate as much heat as polyesters when it sets and the fumes, while not good for you, are not as dangerous as those of many other materials.

Epoxy is the most waterproof material in common use, and it is the primary component in barrier coating applied to hulls to reduce the likelihood of osmotic blistering. It costs more than polyester resin, but it's benefits far outweigh that factor.

Polyster will bond to polyester and sort of bond to vinylester. It will not bond well with epoxy. Epoxy will bond well with polyester and fairly well with vinylester. Vinylester will bond with polyester but not very well with epoxy.
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Old 05-16-2007
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Here read thishttp://www.fibreglast.com/learning_c...tes_repair.pdf
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Old 05-16-2007
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Basically, for repairs, epoxy is the most commonly used resin since it has several notable advantages over polyester and vinylester resin.

As Sailormann has pointed out, epoxy tends to bond better to cured polyester and vinylester resins than polyester or vinylester resins generally do. It is also stronger, which is often important in the case of a repair. It is also far more resistant to water intrusion or osmosis.

However, be careful with epoxies as the chemicals in them are rather nasty, and can cause a severe allergic reaction after prolonged exposure. The fumes are also not too healthy for you, and you need to use an organic vapor filter cartridge mask if you're doing a lot of work with epoxy.

Finally, if you're using any of the fillers, to make thickened resin, you should be using a P95 filter mask at a minimum.

One disadvantage of epoxy is that it loses a lot of its physical strength and softens a bit more under high heat than does polyester or vinylester resins. As that is a problem, it is generally recommended that any epoxy-based laminates—especially those with foam core materials—be painted a very light color if going to be exposed to strong sunlight for extended periods of time. This is actually mentioned in some of the epoxy boat building literature as well.
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Old 05-17-2007
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A few more things about epoxy vs. polyester.

Polyester is actually rather nasty too, and in fact is more dangerous than epoxy in that the MEK in it (or some other volatile compound, I forget) is absorbed rather easily by breathing and also through skin. So, if you work with it and start feeling lightheaded or dizzy - don't be surprized It requires a proper filtering organic respirator and good gloves and sleeves to avoid getting this stuff on your skin. This is one reason many repairmen prefer not to deal with it (confided to me on two separate occasions by two different pro-s).

One more issue which is something to consider - epoxy, while in itself a harder material and better suited for mecanical bonds (think "velcro style" bond), does not have much solvents in it and as such neither penetrates the surface too deeply, nor creates a primary chemical bond with polyester resin. So, when you repair polyester GRP with epoxy - think of it as a big velcro style patch placed on. Since thermal expansion coefficients for epoxy and polyester are different, and the bond is mechanical - it is not impossible for the two compounds to lose their bond over time (since one expands and contracts by a different distance from the other, those little "hooks and loops" can lose their grip). This is one reason, I believe, that I found many failed or very obvious boat deck repairs when made with epoxy. This also may (according to some surveyors) be a reason for "catastrophic failure" of some of those epoxy barrier coat jobs, though being under water I expect them to be less subject to heating and thermal expansion.

So, personally, I prefer polyester resin when repairing decks and superstructure. Epoxy is good for bonding, tabbing - especially wooden parts. It is also easier to use for underwater repairs.

Vinylester is extremely poisonous, more so than polyester, so working with it is probably not for the do-it-yourselfers.

YMMV
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Old 05-17-2007
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brak-

Just curious as to why you think the polyester resin gives a stronger bond, when, if the polyester resin has cured properly, it doesn't leave many sites for new polyester resin to cross-link into. You can read a bit more about epoxy, polyester and vinylester resins at the following links: LINK LINK

Even Don Casey says that Epoxy should be used for repairs, especially those below the waterline. If Epoxy didn't bond better and more strongly than polyester did...why would he recommend using it for such a repair.

Also, this quote is very interesting... and seems to negate your argument for using polyester resin for repairs:

Quote:
1) All repairs are secondary bonds, so they rely upon the adhesive quality of the resin for their strength.

Structural repair theory begins by recognizing the difference between a repair and the original piece. When a part is first fabricated, all the resin in it cures chemically as a single unit regardless of the number or orientation of the reinforcement plies. This is called the primary structure or bond, and it is the strongest form in which a part can exist. Once the part is damaged, all repairs become secondary bonds attached to the original primary structure. In real life, this means that the repair is only as strong as the adhesive used to make it. For this reason, never use a weaker resin than what the part was made with originally. In fact, stronger adhesive resins are sometimes used for repairs. However, even this substitution must be cautiously tested so it does not change the performance of the part.
That was from this website: LINK
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Old 05-17-2007
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Quote:
Originally Posted by sailingdog
brak-

Just curious as to why you think the polyester resin gives a stronger bond, when, if the polyester resin has cured properly, it doesn't leave many sites for new polyester resin to cross-link into.
You are right and most literature says that cured polyester does not create a good primary bond. However "some" is better than none (and also, sometimes, polyester is not completely cured on the surface even after a long time - if the builder used structural polyester and did not cover it from air, so those surfaces may be readily used with more polyester).

The other argument, though, still stands. Thermal expansion of polyester and epoxy is different, and any mechanical bond between them that is subject to temperature variation will also experience different forces from two compounds. Polyester to polyester bond, presumably, will not be subject to these forces since expansion and contraction of same material should be a lot closer in rate.
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