Epoxy vs Polyester

[coopec43]

I'm always surprised when I read comments from people advocating the use of epoxy over polyester because as far as I am concerned they both have a place in boat repair/construction: epoxy for repair, polyester for construction.

I think this article is informative and puts it in a nutshell:

Conclusion
WEST SYSTEM epoxy is the better choice for repairing fiberglass boats. It has excellent adhesive qualities, wets out fiberglass fabrics and it is tough. It has great thin film cure characteristics, cures in cool temperatures and has a long shelf life. Like thousands of boat owners who have successfully repaired their boats, you can use WEST SYSTEM epoxy with complete confidence for fiberglass boat repair.

https://www.epoxyworks.com/index.php...s-boat-repair/

[pcmm]

WEST and other brands have done a great job over the years have done a great job marketing Epoxies to us. In fairness it is easier to work with, has fewer off gasing chemiacals during curing ( styrene in poly) and is less technical to work with. Epoxies don't require alterations in their catalysts and the additions of additives ( air-dry) to work with. They do have higher bond strengths, but Poly has it's place.

I'm building a propane locker right now and went with Poly as its all new construction and poly is 1/3rd the price of epoxy, and it wets our fiberglass much better than epoxy making the task easier.

Both have their places.

[Chotu]

Having been forced to use both, I prefer polyester at this point because it’s so much faster and easier. Waiting for epoxy to kick is a considerable drag on productivity.

Of course bonding is better done with epoxy and exterior below the waterline epoxy wins as well, but building random stuff is way easier/faster with polyester.

I would like to note epoxy has emissions that are just as numerous as polyester. You just can’t smell them as much. But make no mistake. It’s a harsh chemical.

[coopec43]

Originally Posted by Chotu

Having been forced to use both, I prefer polyester at this point because it’s so much faster and easier. Waiting for epoxy to kick is a considerable drag on productivity.

Of course bonding is better done with epoxy and exterior below the waterline epoxy wins as well, but building random stuff is way easier/faster with polyester.

Chotu I couldn't agree more. (I can't believe there are people who want to use epoxy in construction)

[smj]

Polyester/vinylester for new construction but epoxy for any secondary bonds. Only epoxy for any kind of wooden boat construction and also beneficial if looking for lightweight construction.

[rslifkin]

If I'm doing something small, I also tend to gravitate towards epoxy, even for construction. But that's for a couple of reasons: I've worked with it more, and I don't build fiberglass stuff all that often, so I'm more likely to already have epoxy on hand.

[LakeSuperior]

Originally Posted by smj

Polyester/vinylester for new construction but epoxy for any secondary bonds. Only epoxy for any kind of wooden boat construction and also beneficial if looking for lightweight construction.

Only epoxy? Resorcinol is a mechanically stronger wooden joint. However, does not fill gaps.

Resorcinol holds up better under UV exposure.

Resorcinol holds up better under cyclical loading. Epoxy will break down. This may be an important consideration in construction of a wooden boat. I suspect this may have something to do with the distribution of stress in the potentially thicker epoxy glue line.

Resorcinol is more heat tolerant.

Resorcinol does a better job on traditional boat building materials like teak and white oak.

A higher level of workmanship is required to use resorcinol.

[Chotu]

My entire boat is built out of epoxy. So I definitely understand the point of view of preferring it. If anything, polyester suffers from an undeserved bad rep. It’s more a case of right tools for the job/person fabricating.

I now prefer polyester for hand lamination projects since it’s easy to work with and goes along more quickly. My boat was mostly vacuum epoxy infused and hand epoxy layup where appropriate (like the taping in of bulkheads).

People need to shout polyester out a bit more so everyone doesn’t think it’s completely inferior.

I’ve used it just like epoxy in some cases. No mat. I taped in my cabin soles down in the hulls using it and it worked just fine using biaxial tape with no mat bulking. Same weight as using epoxy in that case.

In fact, other than adhesive qualities, it behaves in a very similar way to epoxy. It’s just more stiff/brittle and you need a larger bonding area compared to epoxy to achieve adhesion that’s adequate (but not perfect).

I did a lot of destructive testing before switching over. Polyester can be peeled off epoxy substrate with great effort. So it’s important to use it wisely where depending on it to bond. I wouldn’t use it to try to tape in bulkheads for instance, unless you’re going wet on wet the whole way through. I know it is used for that, but epoxy is way, WAY stronger for mission critical bonding.

Right tools for the right job.

[coopec43]

Originally Posted by smj

Polyester/vinylester for new construction but epoxy for any secondary bonds. Only epoxy for any kind of wooden boat construction and also beneficial if looking for lightweight construction.

I'll go along with that


But I think pcmm is spot on when he says

WEST and other brands have done a great job over the years marketing Epoxies to us.

Now I find people in the US of A don't seem to consider polyester!

[flyingfin]

Also depends upon temperature. Getting the proportion on epoxy is easy - typically 50/50 and epoxy is less sensitive to temperature.

But polyester is drops per ounce. Working in the Florida summer heat,I have seen carefully mixed polyester turn to gel in under 2 minutes before we could spread it over the mat!

[Bill O]

Originally Posted by Chotu

Having been forced to use both, I prefer polyester at this point because it’s so much faster and easier. Waiting for epoxy to kick is a considerable drag on productivity.

Of course bonding is better done with epoxy and exterior below the waterline epoxy wins as well, but building random stuff is way easier/faster with polyester.

I would like to note epoxy has emissions that are just as numerous as polyester. You just can’t smell them as much. But make no mistake. It’s a harsh chemical.

Agree w/most of your comments except unless it was epoxy before, would use vinyl ester (ext. use). This is for the exact reason you mention is the longer lag period w/the epoxy cure. Also if you need to glass large areas the esters are much more economical, but would prefer vinyl for structural purposes vs. poly, while epoxy is the best for structural strength.

Would use epoxy to bond to a previously ester resin, but would not use an ester to bond to a previous epoxy resin due to reduced bonding strength even w/proper surface prep.

We use an private label Mas epoxy and can modify the cure rate w/different ratios of cold/regular kicker when we need to use epoxy.

Most of the inert thickening agents (glass microballoons, fumed silica, etc.) used for the epoxy can be used in the poly/vinyl esters. The fairing filler for epoxy isn't compatible w/the esters though. Read instructions before attempting to use the fillers w/esters.

Both types of esters and epoxies do have fumes that could cause health issues. The chemical off gassing of styrene (fumes) from the ester resins is a potential health hazard and epoxy also releases fumes while curing that can cause sensitization/health issues. Unfortunately Chotu knows too well what health issues arise w/epoxy resin use.

[smj]

Originally Posted by LakeSuperior

Only epoxy? Resorcinol is a mechanically stronger wooden joint. However, does not fill gaps.



Resorcinol holds up better under UV exposure.



Resorcinol holds up better under cyclical loading. Epoxy will break down. This may be an important consideration in construction of a wooden boat. I suspect this may have something to do with the distribution of stress in the potentially thicker epoxy glue line.



Resorcinol is more heat tolerant.



Resorcinol does a better job on traditional boat building materials like teak and white oak.



A higher level of workmanship is required to use resorcinol.

Yet custom wooden boatbuilders seem to gravitate to epoxy?

[valhalla360]

I suspect you see more suggestions of epoxy on forum threads because it's usually repair work that's being discussed or home built boat construction is often using wood coring/cold molded where the better water sealing of epoxy is an advantage.

If I'm just going to keep a bit of one or the around for misc use, it's going to be epoxy because it's more versatile.

[Bill O]

Originally Posted by LakeSuperior

Only epoxy? Resorcinol is a mechanically stronger wooden joint. However, does not fill gaps.

Resorcinol holds up better under UV exposure.

Resorcinol holds up better under cyclical loading. Epoxy will break down. This may be an important consideration in construction of a wooden boat. I suspect this may have something to do with the distribution of stress in the potentially thicker epoxy glue line.

Resorcinol is more heat tolerant.

Resorcinol does a better job on traditional boat building materials like teak and white oak.

A higher level of workmanship is required to use resorcinol.

Resorcinol glue is an excellent product for applications described above and we do use it for outdoor wood to wood joints that will be exposed to UV and saltwater.

Works exceptionally well w/white oak and oily woods like teak (epoxy doesn't bond well w/oak). We just used it on a teak cockpit table since it will be exposed to UV and large changes in temperatures. Downside is you need tight joints (better wood working skills) for a strong bond.