Permeability of Epoxy vs VE vs Polyester

Does anyone have a chart showing the permeability of the different materials. At what point does a material go from below waterline to above waterline?

 

For what purpose, continuous immersion, or day use?

All of them work fine for day use, the cheapest polyesters don't fair as well in continuous immersion though, but the marine versions do. VE will perform great in continuous immersion and so will epoxy.

There is an absorption chart that lists % and strength after many years, I'll see if I can link it.

Found it. This just covers three of their resin types, while the the resin type within a group can vary in performance from one formula to another, and even more from one brand to another, it does give you an idea. A dedicated modern marine version of an ISO polyester may perform much better than a general purpose cheap resin or even a general purpose ISO. The problem is that there are many hundreds of resin formulations that are used, mostly chosen by price, so they cheap ones out number the good ones. And it's the incorrectly used resins that lead to the horror stories.

https://interplastic.com/wp-content/uploads/2020/10/15-year-physical-properties-low-res.pdf

 

Ondarvr. Can I dovetail a question related to it?

Guys here like to do 2x layers or so of ve and then build the bulk in polyester. Seems like its controlled (or at least the perception is) blisters. Was digging through my suppliers list of ve resins and the cross reference of similar blends. Was curios if you could put an asterisk next to or point out which one on the list you'd reccomend for that application?

 

Thank you. That does help.

 

@ondarvr . . . the charts seems to indicate that VE would be the way to go rather than any of the polyester resins. Am I reading them correctly? I have used VE resin in most of my fiberglass work. I actually like working with it more than poly resin, although the fumes are like chemical warfare.

 

Are you focusing on FRP only or also other materials. Permeability of resins depend on the chemical composition and cure process, so there is a huge variation. Also, there is another huge difference between permeablity of water and water vapor. A material that would be 100% impermeable to water, may have high permeability to water vapor. Goretex is a good example of it.

 

Most VEs do very well, it's the exact desired result that narrows it down. Some VEs, like the ones commonly used in a skin coat are formulated to cure in a thin laminate, so you need to be careful if making the laminate too thick due to the exotherm. Others are designed for a thicker laminate, but may not cure well in a thin skin coat situation.

VEs tend to be a bit sluggish in their cure profile, so you need to kick it in the butt for a thorough cure in a thin laminate. If you don't have a good cure the surface profile will change as it post cures out of the mold, plus the physical properties won't be as good, and that includes water resistance.

Many VE skin resins are a VE DCPD blend, this works well for surface profile and cure, VEs don't like to cure and DCPD loves to cure, plus DCPD doesn't shrink much.

 

Yes, VEs tend to perform better in most aspects, but if the "better" performance isn't required in a particular application they aren't used very often, mostly due to cost.