Epoxy or Polyester as I replace large sections of Deck Core

[DerekKelsall]

Originally Posted by drakes

my understanding is you don't put polyester on top of epoxy

once you start with epoxy i would finish with it. i don't understand all the technical details. sure someone else can jump in but it has to do with chemical properties or adhesion.

Hi,
guided by a few decades of experience sailing, designing and building I can relate a few applicable bits of relevant info.
1965 - We used polyester/glass skin over PVC foam which had been coated with epoxy - probably not fully cured. The poly surface cured but left wet resin between the skin and the foam - ripped out. Rule - never use poly over epoxy unless full cured.
We used carbon epoxy pultrusions (like flat bar) as main strength for race tri cross beams - 93 x 50 ft. William Saurin for example. We tested many combinations to find that we got best adhesion using a light wt. csm and poly onto the well abraided carbon epoxy, followed by main poly laminate. Well sanded fully cured epoxy, can have poly laminated over.
1966 - my rule for all specifications for foam sandwich - never spec anything to go into the structure which can rot. - no advantage is gained where there is always a PVC foam suitable. Balsa in decks is a no no and known 50 years ago.
Boats - monos and multis I designed and built are all still sailing unless caught fire or wrecked. - poly, uni E glass, 70-80 kg PVC or Corecell with a good paint spec. all over. Several would be considered extremely light weight today. I have never seen evidence that any one of the hundreds involved would have been one jot better had they been epoxy.
Epoxy - take all the precautions if you must use. (use with timber). No one is immune to the epoxy lurgey, particularly the dust.

KSS, which puts all the info together and does the job of building - for best quality, most time efficient and cleanest workshop.

Happy boating,

Derek

[Souzag818]

Originally Posted by Ken Z

I have used polyester resin on plywood since the 60s, and have had good results, altho epoxy is king and more money. If you started wit epoxy continue with it. Its best to put a coat down, let it get tacky and add stranded cloth 1.75 works, wet it out then you can add woven roven, then stranded, woven etc. until you achieve your thickness, finish with 10 oz, sometimes called surfboard fiberglass. There are different brands of epoxy, west the most known and the most expensive. I ve been using raka in ft. pierce fl @ 772-489-4070.Its a 3-1 mix and for a job that large pumping will wear you out. I fill a measuring cup with water 1 cup, put a clean stick 1/2" wide in it and draw a line, then measure 3 cups and make a line , so in a mixing container put a line at that level, one to three, add hardener first, mix at least two minutes, try to keep it in the shabe. This epoxy doesnt blush unless it gets wet after it sets. I sand in a circular motion with 80 grit before i apply another coat Raka is a little thinner than west and is easy to work, and cheaper. IT sounds like you have do the right steps and i know you dont want to repeat it. Hope this helps.

Woven roving isn't the best thing to use today. Any of the sewn together bi-axel or tri- axel clothes are far superior for strength and ease of wetting out.

[MartinAdelaide]

Originally Posted by toddedger

Sorry guys I've been in the industry working with epoxy for over 30 years. The 120° came directly from Gougeon brothers. Your epoxy will cure, but as soon as the sun shines on it and heats it up it will continue to shrink. Sometimes I wonder why I even bother to help you guys out.

I find that hard to believe since epoxies are exothermic i.e. they give off heat when curing. There is a lower limit to work to, around 20 Centigrade. As for amine blush, you should try better epoxies. I use BoatCote, made in Queensland and it doesn't blush at all. Peel ply is good though, as it keys the layers.

[SV THIRD DAY]

I'm redoing the decks of my Force 50 now...goodbye Teak...hellow Kiwi Grip.
MAS epoxy was damn easy to work with...no the cheapest route, but the material costs are peanuts when you factor in the labor and time.

[Clivevon]

OP mentions using mat, & possibly epoxy.
Not a good idea as the powder binding the chopped strand mat CSM together is not soluble in epoxy, only in polyester or vinylester. You need to use some different combination of materials, not CSM & epoxy. The CSM layer will delaminate from the original polyester,

Guess how I know? See my earlier posting at:

http://www.cruisersforum.com/forums/...-159293-2.html #27.

[glhotka]

Originally Posted by SV THIRD DAY

I'm redoing the decks of my Force 50 now...goodbye Teak...hello Kiwi Grip.
MAS epoxy was damn easy to work with...no the cheapest route, but the material costs are peanuts when you factor in the labor and time.

Thanks Rich, I specifically sought you out as I recalled you mentioning at a boat show we met at that you were redoing your force 50, and given they are pretty much sister ships with the Formosa 51, I figured we could swap some stories. If I recall, you replaced large parts of the core just forward of the coach house all at once, correct?
When you removed the core, what if any support did you put in place to secure the lower skin while you worked on the deck?

Also what thickness core did you go back with?

[rh81]

Sorry guys I've been in the industry working with epoxy for over 30 years. The 120° came directly from Gougeon brothers. Your epoxy will cure, but as soon as the sun shines on it and heats it up it will continue to shrink. Sometimes I wonder why I even bother to help you guys out.

"does not shrink after curing" This is what the Gougeon Brothers say about their Resins (105).

[glhotka]

I would like to thank everyone for their responses. The funny thing is I went to the forum hoping to get clarity on what I found on the web to be conflicting opinions and guidance. The good news is this forum is a microcosm of the rest of the world as there were certainly differing opinions here as well. lol

That said, I think what I have decided (and since I haven't actually done it, it is just a thought right now) and that is to not just worry about the section that I had done, but rather cut a large section and replace the core with fiberglass in a VERY large section. I am thinking of doing this at the widest portion of the deck from the coach house forward about 6 feet. This will be 6 X 15 feet. My thinking is that if I were to replace it all at once, I could get a smoother finish, build up the core a bit thicker, and roll down larger quantities of glass.

I am also thinking now that I should do it with polyester resin because I will be doing it on wood directly. It seems like a lot of work, but I think I would feel better doing it all at once rather than what will end up taking me many months to do in a patch method of doing a 2 x 5 foot section at a time.

I have someone coming over that worked in a shipyard that I will also seek some guidance and steps from to ensure that I am going down the right path. My biggest concern has been the mixing of epoxy and Poly and after this thread, I have deduced that both can be very successful as long as the area is prepared correctly and the layup is done carefully and in the right temperature range.

[valhalla360]

Just a note: Someone suggested that adhesion wasn't that important.


That's absolutely wrong. A cored deck needs solid adhesion between the layers or it will be bouncy (and in a worst case scenario could fail).


To see the difference, take a phone book and try to bend it. If you try to bend the spine it's almost impossible but if you try to bend in the opposite direction it takes almost no effort. The spine has adhesion between the layers but in the other direction it's limited to a small bit of friction. A cored deck works the same way.


PS: I've used plenty of epoxy and read the west system guides and don't recall anything about post curing at 120, so I'm in the don't buy it group.

[neilpride]

Originally Posted by glhotka

I would like to thank everyone for their responses. The funny thing is I went to the forum hoping to get clarity on what I found on the web to be conflicting opinions and guidance. The good news is this forum is a microcosm of the rest of the world as there were certainly differing opinions here as well. lol

That said, I think what I have decided (and since I haven't actually done it, it is just a thought right now) and that is to not just worry about the section that I had done, but rather cut a large section and replace the core with fiberglass in a VERY large section. I am thinking of doing this at the widest portion of the deck from the coach house forward about 6 feet. This will be 6 X 15 feet. My thinking is that if I were to replace it all at once, I could get a smoother finish, build up the core a bit thicker, and roll down larger quantities of glass.

I am also thinking now that I should do it with polyester resin because I will be doing it on wood directly. It seems like a lot of work, but I think I would feel better doing it all at once rather than what will end up taking me many months to do in a patch method of doing a 2 x 5 foot section at a time.

I have someone coming over that worked in a shipyard that I will also seek some guidance and steps from to ensure that I am going down the right path. My biggest concern has been the mixing of epoxy and Poly and after this thread, I have deduced that both can be very successful as long as the area is prepared correctly and the layup is done carefully and in the right temperature range.

May i ask you with what kind of core or Wood you are recoring the deck?

[UNCIVILIZED]

I'm unclear on some of the cost reasonings behind using Polyester. Perhaps because I've never hunted hard to find it on the cheap. But when you can get epoxy for $40-50/gallon it seems like using it then makes that much more sense. Given it's enhanced physical properties. Including bonding much better to marginal surfaces. This, & the fact that if you use it for this kind of job, you've got a much better chance of everything coming out well the first time. And I'd HATE to have to do such a job twice simply because I cheaped out, & went with Poly the 1st time.

Besides, I've pulled WAY too much glass off of cores, or wood, that was put on with polyester. And by pulled off, I mean using nothing more than my fingers, or perhaps a pair of pliers. So I ain't impressed with it's tenacity for sticking to wood. Even if much of what I pulled off was put in in a manner differing from proper industry standards. Since I know that epoxy put onto the same surfaces, in the exact same way, sticks a f**k of a lot better. BTDT, so using Epoxy's a no brainer for me.

Even if using epoxy instead of poly adds $5/sqft to the job, that ain't much compared to the overall job cost. Heck, even if it adds $10/sqft those still aren't loco numbers. Do the math!

[Terra Nova]

Originally Posted by glhotka

...I am also thinking now that I should do it with polyester resin because I will be doing it on wood directly...

Very bad tech.

[ramblinrod]

Originally Posted by Clivevon

OP mentions using mat, & possibly epoxy.
Not a good idea as the powder binding the chopped strand mat CSM together is not soluble in epoxy, only in polyester or vinylester. You need to use some different combination of materials, not CSM & epoxy. The CSM layer will delaminate from the original polyester,

Guess how I know? See my earlier posting at:

http://www.cruisersforum.com/forums/...-159293-2.html #27.

You are correct that the binder in some CSM products is not compatible with epoxy, but there are certainly epoxy compatible CSM products.

[ramblinrod]

Originally Posted by UNCIVILIZED

I'm unclear on some of the cost reasonings behind using Polyester. Perhaps because I've never hunted hard to find it on the cheap. But when you can get epoxy for $40-50/gallon it seems like using it then makes that much more sense. Given it's enhanced physical properties. Including bonding much better to marginal surfaces. This, & the fact that if you use it for this kind of job, you've got a much better chance of everything coming out well the first time. And I'd HATE to have to do such a job twice simply because I cheaped out, & went with Poly the 1st time.

Besides, I've pulled WAY too much glass off of cores, or wood, that was put on with polyester. And by pulled off, I mean using nothing more than my fingers, or perhaps a pair of pliers. So I ain't impressed with it's tenacity for sticking to wood. Even if much of what I pulled off was put in in a manner differing from proper industry standards. Since I know that epoxy put onto the same surfaces, in the exact same way, sticks a f**k of a lot better. BTDT, so using Epoxy's a no brainer for me.

Even if using epoxy instead of poly adds $5/sqft to the job, that ain't much compared to the overall job cost. Heck, even if it adds $10/sqft those still aren't loco numbers. Do the math!

I do the math for every customer quote I prepare. The claim that epoxy "bonds
much better" is false (or at least misguided). For properly applied polyester resin FRP repairs are as strong as the polyester resin FRP, being repaired. You just can't do any better than that. Any additional "adhesion strength" is moot, after the repair has been stressed beyond the capability of the material repaired.

I've been repairing polyester FRP with polyester FRP for 40 years, personally and professionally for over 40 years and have never had a bond failure. Not one. Meanwhile, many of my colleagues who have used epoxy, are now allergic to it, and can't be within 100 ft of it, even in a very well ventilated space (including outdoors), while it is curing (up to 2 weeks).

In my opinion, anyone who uses epoxy where it is not required (other materials are perfectly adequate, such as polyester or vinylester resin) is exposing themselves and others to unnecessary health risk.

Oh and using polyester where appropriate saves the customer money, sometimes a lot of money.

[smj]

Originally Posted by ramblinrod

I do the math for every customer quote I prepare. The claim that epoxy "bonds

much better" is false (or at least misguided). For properly applied polyester resin FRP repairs are as strong as the polyester resin FRP, being repaired. You just can't do any better than that. Any additional "adhesion strength" is moot, after the repair has been stressed beyond the capability of the material repaired.



I've been repairing polyester FRP with polyester FRP for 40 years, personally and professionally for over 40 years and have never had a bond failure. Not one. Meanwhile, many of my colleagues who have used epoxy, are now allergic to it, and can't be within 100 ft of it, even in a very well ventilated space (including outdoors), while it is curing (up to 2 weeks).



In my opinion, anyone who uses epoxy where it is not required (other materials are perfectly adequate, such as polyester or vinylester resin) is exposing themselves and others to unnecessary health risk.



Oh and using polyester where appropriate saves the customer money, sometimes a lot of money.

This is incorrect. Epoxy resin is superior in secondary bonds, and a polyester repair on top of old polyester will not have the same strength as the original layup. Also there are health hazards dealing with polyester resin and MEKP.