Epoxy / Polyester Resins Question

[minaret]

Rod, eventually you will learn that trying to enlighten the masses brings no reward. People who have invested large sums of money in doing it "right", as they have been lead to believe, are heavily invested in that belief. If they choose to believe what you (and I, and every other industry professional who's ever been on this forum) are telling them that means to them that they are suckers who got taken for a ride. They much prefer to not believe that! Doesn't matter that the vast majority of pro yards all do it the same way, the ones who are financially invested in epoxy will get upset if you suggest it's not any better than poly. It comes down to the $ they spent and the perceived value of the vessel. I've talked lots of people on this forum through a full refit using poly only, with excellent results and no problems, getting it done for way less than the epoxy guys and finishing in gel instead of paint (superior finish which cannot be done with epoxy). But you have to get to them before the epoxy guys do. Once they drop a load on epoxy it's too late, they're invested. They don't wanna hear that it wasn't necessary.

I'm sure that as usual I'll be called an amateur for this opinion, despite being one of the few career boatyard guys on this forum, and despite the fact that I've used thousands of gallons of epoxy, far more than the average laminator, having specialized in vacuum bagged carbon/epoxy for many years. For the record however, I couldn't agree with you more. For what it's worth...

[smj]

Originally Posted by minaret

Rod, eventually you will learn that trying to enlighten the masses brings no reward. People who have invested large sums of money in doing it "right", as they have been lead to believe, are heavily invested in that belief. If they choose to believe what you (and I, and every other industry professional who's ever been on this forum) are telling them that means to them that they are suckers who got taken for a ride. They much prefer to not believe that! Doesn't matter that the vast majority of pro yards all do it the same way, the ones who are financially invested in epoxy will get upset if you suggest it's not any better than poly. It comes down to the $ they spent and the perceived value of the vessel. I've talked lots of people on this forum through a full refit using poly only, with excellent results and no problems, getting it done for way less than the epoxy guys and finishing in gel instead of paint (superior finish which cannot be done with epoxy). But you have to get to them before the epoxy guys do. Once they drop a load on epoxy it's too late, they're invested. They don't wanna hear that it wasn't necessary.



I'm sure that as usual I'll be called an amateur for this opinion, despite being one of the few career boatyard guys on this forum, and despite the fact that I've used thousands of gallons of epoxy, far more than the average laminator, having specialized in vacuum bagged carbon/epoxy for many years. For the record however, I couldn't agree with you more. For what it's worth...

I would never refer to you as an amateur but my experiences and beliefs are more in line with boatpokers, polyester for a cosmetic repair on a polyester boat and epoxy for anything structural or below the waterline. I also wouldn't consider boatpoker to be an amateur and have witnessed the same problems as he regarding polyester to polyester secondary bonds.

[Lake-Effect]

Just a thanks to the pros on here, for an interesting discussion.

It's my impression that in professional hull, deck or structural repairs, the labour costs are usually going to swamp the materials costs. Is this a fair statement? Is there a significant difference in the amount of labour involved between pro repairs done in epoxy vs polyester?

(As an amateur, I've only used epoxy, from the belief that epoxy is easier to prepare and use, and generally makes a better physical bond, which increases the odds that my repairs will be successful. So far, I've successfully put gelcoat onto cured epoxy repairs, but none are more than maybe 7 years old, so maybe I will have a surprise down the road)

[Wotname]

Originally Posted by Lake-Effect

Just a thanks to the pros on here, for an interesting discussion.

It's my impression that in professional hull, deck or structural repairs, the labour costs are usually going to swamp the materials costs. Is this a fair statement? Is there a significant difference in the amount of labour involved between pro repairs done in epoxy vs polyester?

(As an amateur, I've only used epoxy, from the belief that epoxy is easier to prepare and use, and generally makes a better physical bond, which increases the odds that my repairs will be successful. So far, I've successfully put gelcoat onto cured epoxy repairs, but none are more than maybe 7 years old, so maybe I will have a surprise down the road)

Yes, another vote of thanks to the pros who have contributed. As the OP, I was hoping for such input and that has been realised so


And having some dissenting viewpoints is always a good thing as it allows (sometimes ) a deeper understanding of the subject.

[boatpoker]

Originally Posted by minaret

Rod, eventually you will learn that trying to enlighten the masses brings no reward. People who have invested large sums of money in doing it "right", as they have been lead to believe, are heavily invested in that belief. If they choose to believe what you (and I, and every other industry professional who's ever been on this forum) are telling them that means to them that they are suckers who got taken for a ride. They much prefer to not believe that! Doesn't matter that the vast majority of pro yards all do it the same way, the ones who are financially invested in epoxy will get upset if you suggest it's not any better than poly. It comes down to the $ they spent and the perceived value of the vessel. I've talked lots of people on this forum through a full refit using poly only, with excellent results and no problems, getting it done for way less than the epoxy guys and finishing in gel instead of paint (superior finish which cannot be done with epoxy). But you have to get to them before the epoxy guys do. Once they drop a load on epoxy it's too late, they're invested. They don't wanna hear that it wasn't necessary.

I'm sure that as usual I'll be called an amateur for this opinion, despite being one of the few career boatyard guys on this forum, and despite the fact that I've used thousands of gallons of epoxy, far more than the average laminator, having specialized in vacuum bagged carbon/epoxy for many years. For the record however, I couldn't agree with you more. For what it's worth...

I have tremendous respect for you and Rod and your positions and perhaps you can do well with that method. You must remember that I see the work of dozens of "professional" tech's and most of them are ..... well less than technically proficient. Many of them are self taught and just do what they've always done without ever looking over their shoulders. There are guys like you two that have 30 years experience then the guys with 1 years experience repeated 30 times. The 30 repeat guys are for the most part the guys I'm up against. So all that on top of seeing hundred of poly on poly secondary bond failures. I'll respectfully (seriously) disagree.

[Three Sisters]

And I need as close to waterproof as possible 99% of the time, so it's three coats of epoxy.

https://www.youtube.com/watch?v=PnXIPV6Jh4Y

[geoleo]

Originally Posted by Wotname

The perceived wisdom is:

1. that cured polyester resin can be over-coated with epoxy resin provided the polyester resin surface is keyed, i.e. the bond is mechanical.

2. that cured epoxy resin should not be over-coated with polyester resin.

3. that cured epoxy resin can be over-coated with epoxy resin provided the surface is keyed, i.e. the bond is mechanical.

If this true, what is the reason that polyester can't be used over epoxy given that the reverse is OK?

because it does not work!...........

[ramblinrod]

Originally Posted by boatpoker

I have tremendous respect for you and Rod and your positions and perhaps you can do well with that method. You must remember that I see the work of dozens of "professional" tech's and most of them are ..... well less than technically proficient. Many of them are self taught and just do what they've always done without ever looking over their shoulders. There are guys like you two that have 30 years experience then the guys with 1 years experience repeated 30 times. The 30 repeat guys are for the most part the guys I'm up against. So all that on top of seeing hundred of poly on poly secondary bond failures. I'll respectfully (seriously) disagree.

I hear you but have to declare, any "properly" completed poly on poly secondary bond repair, is as strong or stronger than original construction. For polyester or epoxy, if completed incorrectly, any bond may fail.

Again if one can use an 8 ton crane for $100/hr or a 10 ton crane for $500/hr, and they only need to lift 3 tons, which solution represents best value for money spent?

If either polyester or epoxy will be adequate for an application, and poly is faster, cheaper, and better (accepts gelcoat without question, delays, and blush removal, which solutuon represents the best value for money spent?

FWIW, I have seen a lot of failed poly bonds in my travels, but as a percentage of material encountered, there's really no diff. Either will generally work welll if used properly, and either may fail if used improperly.

If a poly bond fails, it is always due to one of three reasons:

1. moisture ingress

2. excessive stress

3. improper application

These 3 things will also easily destroy an epoxy job, as will post-cure amine blush and UV exposure.

[NevisDog]

Originally Posted by ramblinrod

... any "properly" completed poly on poly secondary bond repair, is as strong or stronger than original construction...

I'm sure some folks (though perhaps very, very few folks) have figured how to "properly" complete a repair, that will not fail, using cheap polyester resins, and I take my hat off to those folks.

The more important point to get across here is that polyester resin is not, never was, never will be, and is never claimed to be, an adhesive; epoxy resin is. I have no idea how to repair with polyester but I imagine it's quite an achievement, to be admired by all. Lesser mortals should not even try it.

[smj]

"As strong or stronger than original construction"
Can't agree with that one bit.

[boatpoker]

I see many secondary bonds fail right out of the factory. They lay these hulls up so fast and get them out of the mold well before they are ready.

A common bond failure occurs when a liner is fitted within the hull (often glued with plexus or the like) then the joints are glassed over (the secondary). If I spent a little time in my files I could pull out hundreds of factory secondary polyester bond failures like the one below. If they can't do it in the factory what are the odds of Bob the repair guy with bucket of resin in the yard.

[Jim Cate]

Originally Posted by boatpoker

I see many secondary bonds fail right out of the factory. They lay these hulls up so fast and get them out of the mold well before they are ready.

A common bond failure occurs when a liner is fitted within the hull (often glued with plexus or the like) then the joints are glassed over (the secondary). If I spent a little time in my files I could pull out hundreds of factory secondary polyester bond failures like the one below. If they can't do it in the factory what are the odds of Bob the repair guy with bucket of resin in the yard.

BP, I respect your decades of experience, so don't take this as a criticism... it is a genuine question!

The failure in that photo looks like the tabbing material failed rather than the bond. Am I seeing it correctly?

Jim

[boatpoker]

Originally Posted by Jim Cate

BP, I respect your decades of experience, so don't take this as a criticism... it is a genuine question!

The failure in that photo looks like the tabbing material failed rather than the bond. Am I seeing it correctly?

Jim

No offence taken .....The tabbing is polyester and the bond of that tabbing to the liner is a secondary bond failure. This type of tabbing secondary bond failure is also frequently seen on bulkhead and shelf tabbing.

[Wotname]

Originally Posted by boatpoker

No offence taken .....The tabbing is polyester and the bond of that tabbing to the liner is a secondary bond failure. This type of tabbing secondary bond failure is also frequently seen on bulkhead and shelf tabbing.

In general terms, what is the correct (or proper) way to carry out this work so that the secondary bond does not fail?

[boatpoker]

Originally Posted by Wotname

In general terms, what is the correct (or proper) way to carry out this work so that the secondary bond does not fail?

This is where RamblinRod and I disagree. I believe polyester can work even in amateur hands in non-structural or cosmetic applications. For structural or external below water applications I believe for a secondary bond, epoxy is far superior. I do not use polyester in those applications.

Professional Boatbuilder Magazine #66, page 78) "The best study shows that a polyester secondary bond with a 12/1 taper ratio has about 20% the strength of the same thickness of original laminate".