Epoxy and water absorption

You don't need your books. Go to any boat junkyard or look at a wreck that has been submerged for decades.

 

So, are you suggesting uncoated surfaces that you later coat might blister? I understand blistering a bit. I guess I am just trying to understand the point about blistering as it pertains to the OP (and myself in a similar situation). Thanks. Hope it doesn't sound snarky; isn't meant so.

 

I am not suggesting anything. I am just describing another defect/performance characteristic of the material which could be anything from delamination/fatigue/impact/(besides the water absorption and water generation).

My post # 14 is self explanatory and does not need further explanation. The OP topic was water absorption and I already deviated by mentioning water generation. I do not wish to further deviate from the topic.

 

This is a common question that people frequently overthink.

Nothing is waterproof, there are just different degrees of water resistance.

Any epoxy good enough to use in a marine application and used correctly shouldn’t have a problem with water absorption.

Comparing them with polyesters and VEs is a bit troublesome and miss interpretated.

Just about any epoxy will have better physical properties when compared polyester and VEs. The problem is the comparison is frequently done between a good epoxy used correctly, and a production ski boat built with the cheapest possible materials by someone that has no idea of what they’re doing.

This results in people thinking there’s no way a boat should ever be built with something as bad as polyester.

If polyester boat builders used better Marine grade resins, then had a trained crew using good methods, you wouldn’t see many problem hulls out there.

 

Properly cured polyester will absorb up to about 13% water, which puts it at less than the moisture necessary to start the biological process to rot wood. However, it significantly degrades the mechanical properties of the resin. Epoxy is also affected, but to much lesser extent.

 

True, but the “ up to 13%” is a cherry picked number from the typically non Marine grade polyesters.

One of the resin suppliers published a paper on long term immersion effects on the physical properties of several different resins.

It covered good VEs to low cost polyesters.

It revealed about what you would expect, the VE survived well, and the cheapest polyester did the worst.

The results from the cheapest polyester is what was frequently used to prove how bad polyesters were.

The range of performance in polyesters is greater than with epoxies, and the low end is where the polyester market made its living.

 

It is in the terms used. If Maximum Moisture content is used it is 0.85 to 1.25% . In terms of Transverse Diffusivity, it is 10 to 15 for salt water with diffusivity measured in mm2/sec. Test done on Polyester and VE laminates.