Epoxy / Polyester Resins Question

[Cheechako]

Originally Posted by NevisDog

Correct, add #4: that FULLY CURED polyester resin should NOT be over-coated with polyester resin.

The reason is simple: epoxy will stick 'like sh*t to the proverbial blanket', while polyester will only develop a strong bond if applied to other resin that has not been left long enough to fully cure. Epoxy adheres well to timber or ply, for example, while polyester will tend to separate after a few years; its bond to end-grain balsa is more mechanical, from penetrating deep into the soft fibres. Sorry but that's about the extent of my knowledge.

Some very interesting stuff in previous posts about gelcoat (polyester) which I'll now read again, as that's the problem I'm faced with.

What I think I'm hearing is you are saying repairs or mods on a poly boat should not be done with Poly... and that is just false and has been proven for decades.

[Wotname]

Originally Posted by GordMay

“... Andy Miller’s Conclusion
Based on Andy’s and our own testing and experience, I am confident saying WEST SYSTEM Epoxy is a suitable substrate for polyester-based material such as gelcoat. Gelcoat-to-epoxy adhesion will be as reliable, if not better than, a polyester-to-polyester adhesion, providing proper steps are followed throughout the repair process...”

➥ Applying Polyester Gelcoat over Epoxy | Epoxyworks

“... Our test clearly demonstrates that polyester gelcoat will bond to a properly prepared WEST SYSTEM® epoxy as well as to a cured polyester laminate. This test confirms that polyester gelcoats can be applied over cured WEST SYSTEM epoxy on repairs below the waterline...”

➥ https://www.jamestowndistributors.co...t.do?docId=259

And an earlier CF discussion ➥ http://www.cruisersforum.com/forums/...xy-123711.html

Thanks for these links Gord, especially the CF one.

One problem with getting information (of any sort) from just one manufacturer/expert/user etc is that you can never really be sure of it's veracity or whether it is truly addressing the particular inquiry rather than what "they" think you are asking. Whereas CF almost always provide a range of opinions (& facts) etc. Some of it is even informed .

So far I've learned that a good initial bond might not last, a tie coat reduces issues and that perhaps, the culprit for a failed poly over epoxy bond could be long term release of amines from the cured epoxy. Assuming this is so, why doesn't such slow releasing amines affect the bond when epoxy is placed over the poly?

Much of the discussion seems to be using gelcoat over epoxy rather than poly laminating resins over epoxy. Perhaps there are differences between the two especially in terms of flexibility, brittleness and UV transmission. I'm speculating that while gelcoat is UV stable, it might allow very small amounts of UV transmission though to the epoxy underneath using destroying the bond over a period of years. Does anyone have anecdotal evidence of such bonds failing more i high UV environments? I realise this is a difficult question as often high UV environments have higher temperatures to confound the evidence.

Another possible issue with gelcoat is the thinness of gelcoat compared to a poly laminate, i.e. would a poly laminate over a epoxy last better due to the thickness of the poly laminate?

[NevisDog]

Originally Posted by Cheechako

What I think I'm hearing is you are saying repairs or mods on a poly boat should not be done with Poly... and that is just false and has been proven for decades.

Then don't take my word for it - read slowpoker's post above, as he has practical, hands-on experience, while I'm only quoting what i've read in boatbuilding handbooks/journals, but what would they know? Stick with what you've learned, but perhaps share your reliable information sources with others here so they can be sure you are correct?

[NevisDog]

Oops, that last post should have read 'boatpoker', not slowpoker!!! Sorry boat.

[UNCIVILIZED]

Are there not multiple types of polyester resins? Which, this would obviously present several variables in bonding. Both of poly on poly, & poly to epoxy (or vice versa). With some poly resins taking decades to fully cure, if ever. And others do so quite quickly. Which those that aren't fully cured are, I think, easier to repair than those which are.
Maybe someone who wasn't up all night can fill in the blanks on the specific resin types above.

Also, if a resin isn't properly mixed, then it can again, take quite a while to cure, if ever. How many boats have you been down below on, which are far from new, where you catch whiffs of styrene? Lots, right. Some of them decades old. Especially in places with poor ventillation, like cockpit lockers, & anchor lockers up forward.

And when you look at the actual mixing ratios, or more properly catalyzing ratios for poly resins, it becomes readily apparent that one only need goof by the tiniest amount in terms of catalyst, to affect the cure of the resin, as well as it's physical & chemical properties. I mean how many DROPS of catalyst get added to a Gallon of poly resin? So, yeah, goofing by only a few can really screw with things.

Also, the amount of catalyst needed to properly get poly resins to kick can be quite temperature sensitive. Enough so that the ratio that was correct at the start of the day is rather different from that which is ideal come lunch time. And then as temp's plummet as the sun goes down...

Plus you have builders, & boats which are built with laminating resins throughout. Meaning that the final layer(s) aren't done using finishing resin. Which can make for a chemistry nightmare to some degree, when it's time to repair or modify a boat. Non?

Then with epoxies, you're looking at so many formulations that it makes Baskin Robbins 31 flavors look like the number of colors the Model T was offered in. So again, easily a chemistry nightmare akin to the ones above for poly resins. Plus resin's that require post curing, where the heat of post curing will pretty much destroy parts build with room temp epoxies.

Now... Just to throw a wrench into this topic, there ARE Epoxy Gelcoats. Though my experiences with quality paint jobs done with Imron & Awlgrip are exceedingly positive. And of course there are vinyl wraps...

www.Proboat.com (Professional Boatbuilder magazine) is always a good read on these kinds of topics. Giving in depth articles & info on them in various issues. And the articles invariably have great reference links & bibliographies.

Perhaps the final stop (authority) on this stuff, or close to it, are the folks who actually formulate the stuff. Though, yes, I know, at times it's quite difficult to get a straight answer out of them. Or more to the point, a full, & in depth one. As I found out all too well during my 1st boat rebuild. UGH!

If you can get them to divulge their chemical cookbooks, yards that build, & or repair composite boats, tend to have pretty good recipes for what works, & what doesn't. At least in relation to a fraction of the available products out there. Since if they **** up, it means major fiscal losses to them due to having to redo the work... after tearing out the old, bad stuff.
So, ask a pro laminator or three.

PS: We ain't even touched on vinylester resins (yet)
Let alone the "Fun" environmental reg's which govern the use of X, & Y. Which of course vary from municipality to municipality.

[boatpoker]

Originally Posted by UNCIVILIZED

Are there not multiple types of polyester resins? Which, this would obviously present several variables in bonding. Both of poly on poly, & poly to epoxy (or vice versa). With some poly resins taking decades to fully cure, if ever. And others do so quite quickly. Which those that aren't fully cured are, I think, easier to repair than those which are.
Maybe someone who wasn't up all night can fill in the blanks on the specific resin types above.

Also, if a resin isn't properly mixed, then it can again, take quite a while to cure, if ever. How many boats have you been down below on, which are far from new, where you catch whiffs of styrene? Lots, right. Some of them decades old. Especially in places with poor ventillation, like cockpit lockers, & anchor lockers up forward.

And when you look at the actual mixing ratios, or more properly catalyzing ratios for poly resins, it becomes readily apparent that one only need goof by the tiniest amount in terms of catalyst, to affect the cure of the resin, as well as it's physical & chemical properties. I mean how many DROPS of catalyst get added to a Gallon of poly resin? So, yeah, goofing by only a few can really screw with things.

Also, the amount of catalyst needed to properly get poly resins to kick can be quite temperature sensitive. Enough so that the ratio that was correct at the start of the day is rather different from that which is ideal come lunch time. And then as temp's plummet as the sun goes down...

Plus you have builders, & boats which are built with laminating resins throughout. Meaning that the final layer(s) aren't done using finishing resin. Which can make for a chemistry nightmare to some degree, when it's time to repair or modify a boat. Non?

Then with epoxies, you're looking at so many formulations that it makes Baskin Robbins 31 flavors look like the number of colors the Model T was offered in. So again, easily a chemistry nightmare akin to the ones above for poly resins. Plus resin's that require post curing, where the heat of post curing will pretty much destroy parts build with room temp epoxies.

Now... Just to throw a wrench into this topic, there ARE Epoxy Gelcoats. Though my experiences with quality paint jobs done with Imron & Awlgrip are exceedingly positive. And of course there are vinyl wraps...

www.Proboat.com (Professional Boatbuilder magazine) is always a good read on these kinds of topics. Giving in depth articles & info on them in various issues. And the articles invariably have great reference links & bibliographies.

Perhaps the final stop (authority) on this stuff, or close to it, are the folks who actually formulate the stuff. Though, yes, I know, at times it's quite difficult to get a straight answer out of them. Or more to the point, a full, & in depth one. As I found out all too well during my 1st boat rebuild. UGH!

If you can get them to divulge their chemical cookbooks, yards that build, & or repair composite boats, tend to have pretty good recipes for what works, & what doesn't. At least in relation to a fraction of the available products out there. Since if they **** up, it means major fiscal losses to them due to having to redo the work... after tearing out the old, bad stuff.
So, ask a pro laminator or three.

PS: And we ain't even touched on vinylester resins
Let alone the "Fun" environmental reg's which govern the use of X, & Y. Which of course vary from municipality to municipality.

+1 You have also just enumerated a number of issues among the main causes of blisters.

[UNCIVILIZED]

Originally Posted by boatpoker

+1 You have also just enumerated a number of issues among the main causes of blisters.

Which in layman speak, are areas of delamination. Ones sometimes filled with pockets of uncured chemical components of resin, & or gelcoat. That of course look horrid, especially when they're above the waterline. But are more commonly present below it, due to moisture levels in those regions, both inside, & outside of the boat.

Plus of course, they're sources of structural weaknesses, contributing to a boat's further demise if left untreated. Untreated being a key word, as to some degree blisters are self-replicating, just like a virus, or cancer cells. Much like plywood when it begins to seperate/delaminate in a manner akin to a deck of cards come adrift. It too has a growing, terminal disease (or several of them).

[ramblinrod]

Originally Posted by boatpoker

For structural bonds I completely agree. Boat builders have proven for decades that fresh polyester will not adhere to cured polyester but epoxy will if properly prepared. Some boat builders popped the hull out of the mold and let them cure before bonding the stringers or bulkheads. This is the major reason I seen so many failed tabs and stringers.

Gelcoat on epoxy (if well keyed ) will likely work well enough as the stresses are much lower than the structural bonds of items such as bulkheads.

I disagree. For over 40 years, manufacturers and pro repair people have been repairing polyester FRP and gelcoat with polyester FRP and gelcoat. Millions and millions of boats.

When I begin a repair (personally or professionally) I ask myself, "can I use polyester?" If the answer is "Yes" (and it is in every case except epoxy built boats, which are relatively few), I use polyester for the following reasons:

1. Perfectly adequate adhesion strength to polyester FRP and wood.
2. Perfectly adequate tensile/compression strength
3. Perfectly adequate flexural modulus.
4. Only one catalyst required for all temp conditions.
5. Polyester and gelcoat can go over it with NO risk of future bond failure due to chemical incompatibility.
6. Lower risk of uncurred product spontaneous combustion.
7. Lower risk of allergic reaction/contact dermatitis development.

Of course DIY epoxy marketeers will jump on and cling to any claim, that gelcoat can be applied over epoxy. I've done it. Some times it works fine, if one has all the time needed for the epoxy to fully cure (which can take up to 2 weeks or even longer). What is sufficient cure time in a non climate controlled environment? Nobody knows until the bond fails, perhaps years later, or doesn't.

[boatpoker]

Originally Posted by ramblinrod

I disagree. For over 40 years, manufacturers and pro repair people have been repairing polyester FRP and gelcoat with polyester FRP and gelcoat. Millions and millions of boats.

Please re-read my post, I never said that wouldn't work (for cosmetic repairs) but if you are talking structural repairs then yes we disagree. I've seen many failures right out of the factory when polyester was taped or tabbed over cured resin.

[ramblinrod]

Originally Posted by ramblinrod

I disagree. For over 40 years, manufacturers and pro repair people have been repairing polyester FRP and gelcoat with polyester FRP and gelcoat. Millions and millions of boats.

When I begin a repair (personally or professionally) I ask myself, "can I use polyester?" If the answer is "Yes" (and it is in every case except epoxy built boats, which are relatively few), I use polyester for the following reasons:

1. Perfectly adequate adhesion strength to polyester FRP and wood.
2. Perfectly adequate tensile/compression strength
3. Perfectly adequate flexural modulus.
4. Only one catalyst required for all temp conditions.
5. Polyester and gelcoat can go over it with NO risk of future bond failure due to chemical incompatibility.
6. Lower risk of uncurred product spontaneous combustion.
7. Lower risk of allergic reaction/contact dermatitis development.

Of course DIY epoxy marketeers will jump on and cling to any claim, that gelcoat can be applied over epoxy. I've done it. Some times it works fine, if one has all the time needed for the epoxy to fully cure (which can take up to 2 weeks or even longer). What is sufficient cure time in a non climate controlled environment? Nobody knows until the bond fails, perhaps years later, or doesn't.

Whoops. Sorry boat poker, this was supposed to be in response to another post and I accidentally quoted yours.

[MarkSF]

I've tried putting gel coat over West System epoxy, and it wouldn't cure, not ever, and I waited 2 weeks. Gel coat that I mixed at the same time, but was over polyester, cured in 2 hours. I cleaned the epoxy carefully beforehand to remove any amine blush. Unless there is a predictable method to ensure it cures, I'll never waste my time in this way again.

[boatpoker]

Check out what MAS has to say about epoxy, vinylester and polyester attributes. I agree with every single thing they say.

[ramblinrod]

Various comments to your post in blue.

Originally Posted by UNCIVILIZED

Are there not multiple types of polyester resins?

Absolutely! In my service vehicle (boat repair) I carry epoxy with medium cure hardener, isopthalic polyester resin, white gelcoat, Duratek, styrene, acetone, MEKP, neutral gelcoat, Interprotect 2000E, and array of pigments, various glass fabrics.

On special occasions, I will bring in different chemicals for different requirements.

Which, this would obviously present several variables in bonding. Both of poly on poly, & poly to epoxy (or vice versa).

For sure!

With some poly resins taking decades to fully cure, if ever. And others do so quite quickly. Which those that aren't fully cured are, I think, easier to repair than those which are.

No resin is ever 100% cured. IOW never, ever is a resin fully cured. My polyester FRP boat, over 40 years old, is still curing. Same goes for epoxy. Under normal conditions, all will be about 90% cured +/- in about 2 weeks, but continue to cure indefinitely.

Maybe someone who wasn't up all night can fill in the blanks on the specific resin types above.

As many different kinds as there are boats, too numerous to list.

Also, if a resin isn't properly mixed, then it can again, take quite a while to cure, if ever. How many boats have you been down below on, which are far from new, where you catch whiffs of styrene? Lots, right. Some of them decades old. Especially in places with poor ventillation, like cockpit lockers, & anchor lockers up forward.

Yup, this is due to that forever curing thing. If epoxy had an off-gas as pungent as that of styrene, you would smell that too.

Which is one place I forgot to mention in a previous post where I would choose to use epoxy over poly; if the smell of the poly would be too offensive. e.g. Inside repairs where folks needed to sleep that night with poor ventilation.

And when you look at the actual mixing ratios, or more properly catalyzing ratios for poly resins, it becomes readily apparent that one only need goof by the tiniest amount in terms of catalyst, to affect the cure of the resin, as well as it's physical & chemical properties.

True of both poly and epoxy. It's proportional. If one is out +/- 10%, no harm no foul. That MEKP catalyst to poly, is generally 0.5 to 2.0% compared to hardener to epoxy, which may be 20% to 100% depending on make and model, has little bearing. +/- 10% is always the target. With poly catalyst, one is just using a smaller graduated vessel than for epoxy hardener.

I mean how many DROPS of catalyst get added to a Gallon of poly resin? So, yeah, goofing by only a few can really screw with things.

Incorrect. To a US gallon of poly (128 oz), one would add somewhere between 0.6 and 2.6 oz of MEKP catalyst, depending on the pot life / cure time required.

Also, the amount of catalyst needed to properly get poly resins to kick can be quite temperature sensitive. Enough so that the ratio that was correct at the start of the day is rather different from that which is ideal come lunch time. And then as temp's plummet as the sun goes down...

This is also true of epoxy, even more so, but with epoxy, you cannot simply change the ratio of the one catalyst used (as with poly) you have to have on hand, and use different hardeners with different cure characteristics. If you use fast cure epoxy hardener on a hot day, have a fire extinguisher handy. If you use slow cure epoxy on a cool fall day, wait for spring for it to harden.

Plus you have builders, & boats which are built with laminating resins throughout. Meaning that the final layer(s) aren't done using finishing resin. Which can make for a chemistry nightmare to some degree, when it's time to repair or modify a boat. Non?

Mostly false. Any builder with any know-how, knows to use a laminating resin curing agent to fully cure in air. Methods include adding a wax additive, covering with PVA (poly vinyl alcohol) or in cases of flat surfaces, covering with wax paper, or if being finished, covering with gelcoat, with an air cure additive or other methods above.

Then with epoxies, you're looking at so many formulations that it makes Baskin Robbins 31 flavors look like the number of colors the Model T was offered in.

Yup! (But the same really holds true for poly.)

So again, easily a chemistry nightmare akin to the ones above for poly resins.

A little over-dramatic. I don't lay awake at night shivering in fear about tomorrow's FRP tasks. ;-)

Plus resin's that require post curing, where the heat of post curing will pretty much destroy parts build with room temp epoxies.

Yup! (But one wouldn't use these materials / techniques if this was to be an issue.)

Now... Just to throw a wrench into this topic, there ARE Epoxy Gelcoats.

Could be, I'm not personally aware of any, and have never used any.

Though my experiences with quality paint jobs done with Imron & Awlgrip are exceedingly positive.

These are not gelcoats, far from it. All they have in common is that they are an exterior finish containing pigment. Gelcoat is much more durable, has much thicker DFT (Dry Film Thickness) ) and is far easier to repair, than paint.

And of course there are vinyl wraps...

www.Proboat.com (Professional Boatbuilder magazine) is always a good read on these kinds of topics. Giving in depth articles & info on them in various issues. And the articles invariably have great reference links & bibliographies.

Yup, but little to do with an epoxy / poly discussion. A vinyl wrap will go over either. It would be like saying, there are also adhesive/sealants. Correct, but little to do with the actual discussion.

Perhaps the final stop (authority) on this stuff, or close to it, are the folks who actually formulate the stuff. Though, yes, I know, at times it's quite difficult to get a straight answer out of them. Or more to the point, a full, & in depth one. As I found out all too well during my 1st boat rebuild. UGH!

Manufacturers are generally very knowledgeable about their own product. The customer contact person, not so much sometimes. It is very common (and common sense) that a manufacturer will promote the use of their product, where another would be better. Eg. West Systems promoting applying poly gelcoat over standard epoxy, when it is far better/safer to put poly gelcoat over poly resin.

If you can get them to divulge their chemical cookbooks, yards that build, & or repair composite boats, tend to have pretty good recipes for what works, & what doesn't.

You have to be a little careful, as it can get into a blonde/brunette/redhead issue (personal preference or what one grew up on).

At least in relation to a fraction of the available products out there. Since if they **** up, it means major fiscal losses to them due to having to redo the work... after tearing out the old, bad stuff.

Yup! It is very common for a pro to go with what they know, as introducing variables can have a huge cost if they don't go as planned. E.g. I really enjoy the BoatWorks today videos, but that is just one data source. While I don't disagree with his findings applying polyester over epoxy for that one case, that was one test sample under one set of conditions, with no long term evaluation, which is nothing to base a general conclusion on (which a West Systems marketer jumped all over). Additionally, he tried to make a properly mixed batch of poly resin catch on fire and concluded it couldn't be done. Perform that same test with epoxy and fast cure properly mixed hardener on a hot day, in a tall container, and poof, 5 alarm. I know a fella (via internet only) that destroyed a beautiful Flicka 20, from that very cause.

I use epoxy for FRP seminars I conduct, (due to the low smell in confined, not so well ventilated areas) and demonstrate just how dangerous it can be while curing. Yes, yes, yes, poly can be over-catalyzed to make a "hot" batch, but properly catalyzed, you almost have to try to make it spontaneously combust, and any batch that is mixed so hot, will have very poor cured properties.

[Saltyhog]

Originally Posted by boatpoker

Check out what MAS has to say about epoxy, vinylester and polyester attributes. I agree with every single thing they say.

MAS is in the business of selling... wait... what? Oh yeah, EPOXY!

[boatpoker]

Originally Posted by Saltyhog

MAS is in the business of selling... wait... what? Oh yeah, EPOXY!

That does not mean they are wrong. Their position coincides with my experience over somewhere around 4500 surveys and insurance investigations.