Epoxy or Polyester as I replace large sections of Deck Core

[Souzag818]

Originally Posted by smj

Absolutely! That's why I wouldn't hire anyone that insists on using polyester for a structural repair.

Couldn't agree more...

[lateral]

Agreed, Without giving you options/caveats of each & $'s.

My boat was originally was strip plank resorcinol glued & it failed.
The glue lines opened, so resorcinol is crap?
The builders decision making was crap.

Resorcinol = perfect mating plus high clamp- which mine had neither.
He probably would have succeeded with epoxy.

[ramblinrod]

Originally Posted by smj

I have seem many failed poly to poly secondary bonds, not just the one on my old catamaran.

Epoxy doesn't stick to air, wax, grease, water, or dust, any better than poly does.

Both will fail miserably if prep or application is poor.

Both will stick fabulously if prep and application is good.

Since poly is much better for laminating than epoxy, and poly can be easily gelcoated, for most structural and/or cosmetic repairs on a poly boat, poly is by far the better resin to use.

(It's an added benefit that poly is less likely to spontaneously combust while curing, inflict you with health problems, or cost so much money.)

If after all this, anyone still wishes to use epoxy to repair their poly boat, I really could care less.

But to tell others they must use epoxy to make safe and reliable repairs on poly? That's just total BS. There are over a million boats on the water to prove that poly on poly works just fine for both primary and secondary bonds.

[lateral]

(It's an added benefit that poly is less likely to spontaneously combust while curing, inflict you with health problems, or cost so much money.)

All red herrings, IMO, or should I say blue.
Poly reaction is also exothermic - never done a hot coat &
melted a cup with the remainder?
Poly is way more flamable as it contains solvent.
MEKP is a stronge oxidising agent & toxic, not to mention explosive with accelerators. (Cobalt, DMA) Must be kept as dangerous goods in quantity.
Dimethylaniline accelerator is a known carcinogen.
The thinner in Poly (styrene monomer) necessitated my leaving the industry.
My cost: west $325/25L resin & hardener
Poly iso $250/25L resin & hardener

Epoxy is more benign if you keep sensitization at bay.
I still use poly, for the right application with good PPE.

[Souzag818]

"Epoxy doesn't stick to air, wax, grease, water, or dust, any better than poly does." Funny thing is I had drops of epoxy stuck on my shop floor that were there for years, without any prep to the dirty plywood. So I think that's BS. Imagine if it were properly prepared and applied...So if people want to waste money on poly, and have an "adequate" repair, I couldn't care less.

[neilpride]

Originally Posted by Souzag818

"Epoxy doesn't stick to air, wax, grease, water, or dust, any better than poly does." Funny thing is I had drops of epoxy stuck on my shop floor that were there for years, without any prep to the dirty plywood. So I think that's BS. Imagine if it were properly prepared and applied...So if people want to waste money on poly, and have an "adequate" repair, I couldn't care less.

With the same logic i have a friend with a 60 X 45 pool covered with 2 CSM layers and in poly sticked to cement and doing great after 10 years...

[keith4001r]

Subscribed

[softdown]

My wetted area has a number of blisters that are growing smaller in the desert environment after being on a slip for years and years.

I have 1.5 gallons of epoxy resin that I am considering using to help make the wetted area more water resistant. Then use two gallons of Pettit Trinidad before usage in the Gulf Of Mexico.

Planning to sell in two years, I want to do a good job but not necessarily a great job.

Serious problems with this idea?

I studied bottom prepping enough to get totally confused by all the ideas and theories.

[Terra Nova]

Originally Posted by softdown

...Serious problems with this idea?...

Yeah, strive for a great job and hope you get a good one.

[s/v Jedi]

Originally Posted by Terra Nova

Yeah, strive for a great job and hope you get a good one.

Exactly. Don't do the "I got 1.5 gallons of epoxy, what can I do with that" approach but rather "how much of which product do I need to fix this?"

[er9]

Ok so here is my experience with polyester and epoxy resins as i was taught just to add even more confusion to the discussion.

I worked for a company for 15 years that developed and manufactured polyesters , epoxies and urethanes etc...for almost 50 years. The owner was a chemist in the 1950's (Norry Hastings) that helped develop some of the original formulas for many of the resins. he worked with the govornment, military and business sector. we provided material for the original stealth bombers and various other programs. was a cool place to work he was genuinely a brilliant man.

When i worked for the company i was responsible for manufacturing (actually mixing and making the resins from scratch), selling and working with all of the resins we sold to the public...i will admit i have limited experience fiberglassing boats specifically but i have worked extensively with epoxy, polyesters and urethanes.

this is the basics of what i was taught and what i learned from accumulated knowledge using the resins. take it with a grain of salt as my knowledge ends in the mid 2000's but the core ingredients dont seem to have changed much. i am a bit out of touch with new resins, cloths and techniques though but i think some of what i learned is still relevant.

not all resins are created equal and knowledge of a particular resin, technique and skill using them can make or break the properties of a good resin or enhance a bad one. a good quality resin from a reputable supplier and a fresh resin are ideal.

as far as using polyester over old polyester...we were taught and my experience has proven that if its properly prepped it a perfectly good way to repair old polyester. there are differences in polyester resins though. for example laminating polyesters do not have a wax additive and were always used only for the layup with cloth or matt no matter how many layers. the reason was simply there was no additive to cause a bond failure. we were taught that only the last and final layer would you use a polyester with a wax additive if you used one at all. this will prevent delamination when the heat of the sun starts to expand and contract the resin on a daily basis. technique was king though as resin rich laminates or poor or sloppy prep was counter productive.

as far as polyester and wood...was not a good combination. polyester over any tropical wood or any naturally oily wood is a very bad mix from our experience as the natural oils in the wood act as a release agent. even have to be carefull using epoxy over very oily tropical woods. i have seen some nasty delaminations where polyester was used over tropical woods two or three years later after repeated expansion and contractions. the oilier the wood, the faster the delamination. if we were going to use polyester over any wood we would prep it by adding styrene monomer to polyester at 10% volume or less, less is better (makes it watery thin) and soaking the wood with this mix and letting it mostly cure. do not use acetone for this as it can cause problems later. once mostly cured but still tacky we began glass layup and you would get the best bond you could get between the two.

epoxies were always the choice for bonding and structural applications. we worked with many structural repair guys and casting epoxies or medium to slow cure epoxies (non filled) were the the preferred choice. reason being their bond to pretty much any surface and their strength. a properly mixed and cured slow to medium set epoxy is god damn tough. epoxies tend to remain soft and flexible (not always perceivable) and its this resilience that helps with their strength and adhesion properties. polyesters on the other hand in comparison are always brittle. i say slow to medium pot life epoxies as opposed to fast set because the heat generated in curing can make even laminating epoxies more brittle.

all that being said if you already used epoxy you really do want to finish with it because polyester may appear to bond to epoxy...and it will for a time...over time though expansion and contraction forces will cause delamination between the two, i have seen a lot of it. may not be a year or two but it will eventually happen and our boats are in the elements 24/7. not a choice i would make. when laminating with epoxy we always did as much of the lamination as possible, at once. if we did have to stop and let the epoxy lamination set and partially cure, we always prepped it by cleaning with solvent and or lightly sanding it before continuing. epoxies have a natural oil that settles on the surface during cure and can actually act as a release to itself so we always had to be carefull. casting epoxies were the worst for this as opposed to potting, tooling or laminating epoxies.

having said all this, if your still reading, personally i would do most all repairs of polyester with polyester with the exception of bonding to wood, filling voids or areas where higher structural strength is desired. i want to re-glass some of my bulkhead tabbing soon and will do it with a good quality laminating epoxy as it will bond over the original wood and polyester already there.

hope some of this was helpfull to someone.

[softdown]

Originally Posted by er9

Ok so here is my experience with polyester and epoxy resins as i was taught just to add even more confusion to the discussion.

I worked for a company for 15 years that developed and manufactured polyesters , epoxies and urethanes etc...for almost 50 years. The owner was a chemist in the 1950's (Norry Hastings) that helped develop some of the original formulas for many of the resins. he worked with the govornment, military and business sector. we provided material for the original stealth bombers and various other programs. was a cool place to work he was genuinely a brilliant man.

When i worked for the company i was responsible for manufacturing (actually mixing and making the resins from scratch), selling and working with all of the resins we sold to the public...i will admit i have limited experience fiberglassing boats specifically but i have worked extensively with epoxy, polyesters and urethanes.

this is the basics of what i was taught and what i learned from accumulated knowledge using the resins. take it with a grain of salt as my knowledge ends in the mid 2000's but the core ingredients dont seem to have changed much. i am a bit out of touch with new resins, cloths and techniques though but i think some of what i learned is still relevant.

not all resins are created equal and knowledge of a particular resin, technique and skill using them can make or break the properties of a good resin or enhance a bad one. a good quality resin from a reputable supplier and a fresh resin are ideal.

as far as using polyester over old polyester...we were taught and my experience has proven that if its properly prepped it a perfectly good way to repair old polyester. there are differences in polyester resins though. for example laminating polyesters do not have a wax additive and were always used only for the layup with cloth or matt no matter how many layers. the reason was simply there was no additive to cause a bond failure. we were taught that only the last and final layer would you use a polyester with a wax additive if you used one at all. this will prevent delamination when the heat of the sun starts to expand and contract the resin on a daily basis. technique was king though as resin rich laminates or poor or sloppy prep was counter productive.

as far as polyester and wood...was not a good combination. polyester over any tropical wood or any naturally oily wood is a very bad mix from our experience as the natural oils in the wood act as a release agent. even have to be carefull using epoxy over very oily tropical woods. i have seen some nasty delaminations where polyester was used over tropical woods two or three years later after repeated expansion and contractions. the oilier the wood, the faster the delamination. if we were going to use polyester over any wood we would prep it by adding styrene monomer to polyester at 10% volume or less, less is better (makes it watery thin) and soaking the wood with this mix and letting it mostly cure. do not use acetone for this as it can cause problems later. once mostly cured but still tacky we began glass layup and you would get the best bond you could get between the two.

epoxies were always the choice for bonding and structural applications. we worked with many structural repair guys and casting epoxies or medium to slow cure epoxies (non filled) were the the preferred choice. reason being their bond to pretty much any surface and their strength. a properly mixed and cured slow to medium set epoxy is god damn tough. epoxies tend to remain soft and flexible (not always perceivable) and its this resilience that helps with their strength and adhesion properties. polyesters on the other hand in comparison are always brittle. i say slow to medium pot life epoxies as opposed to fast set because the heat generated in curing can make even laminating epoxies more brittle.

all that being said if you already used epoxy you really do want to finish with it because polyester may appear to bond to epoxy...and it will for a time...over time though expansion and contraction forces will cause delamination between the two, i have seen a lot of it. may not be a year or two but it will eventually happen and our boats are in the elements 24/7. not a choice i would make. when laminating with epoxy we always did as much of the lamination as possible, at once. if we did have to stop and let the epoxy lamination set and partially cure, we always prepped it by cleaning with solvent and or lightly sanding it before continuing. epoxies have a natural oil that settles on the surface during cure and can actually act as a release to itself so we always had to be carefull. casting epoxies were the worst for this as opposed to potting, tooling or laminating epoxies.

having said all this, if your still reading, personally i would do most all repairs of polyester with polyester with the exception of bonding to wood, filling voids or areas where higher structural strength is desired. i want to re-glass some of my bulkhead tabbing soon and will do it with a good quality laminating epoxy as it will bond over the original wood and polyester already there.

hope some of this was helpfull to someone.

Epoxy resin:
1) Is stronger
2) Ages better due to handling expansion and contraction better due to superior pliability
3) Adheres better to more materials with a stronger bond.
4) Significantly better water intrusion resistance. AKA: Less enabling of osmosis.

This is what I picked up from your explanation plus a few others. Epoxy resin costs more but not that much more. I don't see why a boat owner would use polyester resin unless they already had it and were sure it would be fine for the job at hand.

Also....thanks for more pointers on resins.

[Colin A]

ER9,
Thanks for the post, my experience and what I was taught when I went to trade school for composites are very similar to what you write. I would also add on boding wood with polyester I was trained to always use chop strand mat (CSM) as the first layer when laminating with poly to wood. Based on experience after that training including some experiments with building battery boxes and leaving them in the back yard un, I have to say if you do want to bond poly to wood prep as ER9 stated then use CSM as your fist layer.

[Terra Nova]

9--good post.