Epoxy or Polyester Resin

[campbell]

Folks I was under the impression that the inner hull skins from Aquasport factory were most likely laid using epoxy resin. Recently after discussion with some other people in the marine industry they told me that it was most likely polyester resin. Now im confused, I was planing on using epoxy resin for all of my rebuild...... any thoughts on the subject? Ive heard it both ways I dont want to rebuild with the lesser secondary bond so........ any help is appreciated. Its an 1984 222 if it matters.

Thanks,
KRC

[wingtime]

Pretty much all boats are made with some form of Polyester resin.  Gel coat will not stick to epoxy.  So if it has gel coat on it it's polyester. The reason?  Polyester will not stick to epoxy.  Gel coat is made out of polyester.  Epoxy will stick to anything and has a MUCH higher bond strength then polyester.  For the strongest repairs with the best bond, I always use epoxy. (I like MAS)  The problem is if you have to put gel coat back on it you might have trouble getting it to stick.    Also polyester is not as waterproof as epoxy.  There are certain types of polyester you do not want below the waterline.  I'd try to find a fiberglass dealer near you.  Don't go to a retail place.  Those resins have inhibitors in them to extend the shelf life but it effects how well they cure.   If it's a structural repair I'd use epoxy.  It's usually twice as expensive as polyester though.  I recently rebuilt my fuel tank coffin cover.  I was going to use epoxy but the rep at Fiberglass coatings talked me into a quality polyester for the first few layups and secondary bond, then a less expensive polyester for the rest of the layups.  Came out great.  However this was a non structural repair that is above the water line and I'm not gel coating it.

[campbell]

I was speaking with a manufacturer of a poured transom material and they told me that their product would only bond to polyester resins.  So any rebuilding where I tie into the transom would also have to be done with polyester resins.  However If i were to use coosa for the transom then they tell me i can use any resin I like.  Anyone weigh in on this?

-KRC

[slippery73]

Don't waste your time with epoxy, its pointless. Get vinylester if your concerned with strength its compatible with all polyesters.

[LilRichard]

I would not go so far to say epoxy is pointless - in fact in high stress areas it is a very good thing to use (like rebonding stringers, etc).  

However I also will say that ALL Aquasports were made with polyester, and I think using polyester correctly will yield fine results for your rebuild.  And polyester is fine below the waterline - your hull is made of it, and 50% of it is below the waterline!

[wingtime]

I'd be leery of saying that polyester is fine below the water line.  Not all polyesters are created equal.  Most polyesters should NEVER be used for a repair below the waterline.  Yes our boats are made of polyester, but that is industrial quality stuff and I'm sure the first few layers of resin to go in the mold are the more water impervious type.  Also all those layers are adhered during a PRIMARY chemical bond.  If I'm doing a repair that will be in contact with the water I'd use a vinylester or at least epoxy for a barrier coat.

[LilRichard]

WT - you obviously have to put either gelcoat or paint over repairs of course - but I rebuilt my entire boat with polyester, and a lot of it is below the waterline.  DOH!!!

 

Not trying to beat the horse, but saying polyester should not be used below the waterline is completely FALSE, and it is not something you should state on a forum if you don't know the facts.  Saying it might not be as good as epoxy, that's a different argument to which I agree there are valid points.  

And you're saying that the boat was built with "industrial quality" resin?  I Don't follow that logic - it's all the same if you buy quality stuff.  Please tell me how the resin they used to build the hull is superior to FGCI laminating resin?

Don't take my word for it, call over to FGCI and get their advice... or ask Joel on bateau.com

[damnitbadger]

Epoxy is superior to poly, no question about that. For their intended use both are adequate provided they are finished properly. Epoxy is more expensive and stonger therefore if you are doing structural repairs like a transom I would go with epoxy. Poly is fine for all repairs as well and will take a gel coat which can be sanded to match hull repairs. Exposed poly layup will over time absorb water where epoxy is much more resistant to water absorption. If you trailer your boat like most here do, wet hulls are not a problem. Bottom line is both are good products and will do the job but one is more labor intensive and costly but stronger. Proper finish is key. I would not hesitate to use either product for any repair. I opted for epoxy on the transom of my 222CCP because I used bluewater coosa board and a bracket in the rebuild and wanted the additional strength. All of our Aquasports were made of poly resin. It is a good cost effective means of boat building and repair.

[wingtime]

Please tell me how the resin they used to build the hull is superior to FGCI laminating resin?

Don't take my word for it, call over to FGCI and get their advice... or ask Joel on bateau.com

OK it's simple store bought resin has a large amount of inhibitors in it to extend the shelf life.  Resin that is going to be used by right away by a factory from a 55 gallon drum does not.  These inhibitors greatly effect the bonding ability of the resin.   My post was aimed to the builder who is going to a retail location for his supplies.  

In the case of Fiberglass coatings, THEY are the ones who told me about these issues.  In fact on the FGCI web site it says :

NGR or boatyard resin:    1.  Inexpensive  2. Highly inhibited for longer shelf life   3. Stays liquid longer   4. Shouldn't be used below the waterline   5. Shows cosmetic defects

GP Marine resin:    1.  Highly inhibited for longer shelf life   2. Fast wet-out   3. A good industrial laminating resin   4. Water can bleed through and cause blisters or laminating problems

Boat Builder or Low Profile:   1. Designed for boats that don't stay in the water   2. Higher heat temperature distortion   3. Better water resistance   4. Low shrink - good cosmetically

I think this answers the original posters question.  Yes epoxy if FAR better for repairs.  But it is much more expensive.  Poly is good for most repairs but it's secondary bond (adhering to cured resins) is not even in the same ball park as epoxy.

[RickK]

Thanks for the explanation WT  
I'm not really sure what it explained as far as which is best - looks like all of the ones you listed were suboptimal  

[Mad Dog]

Here is a quote from Bateau2.com.  The same question was asked over there.

" the end, it is your decision.
Who are you going to believe? A guy that once had a vague job with a boat building company or a yacht designer that was director of engineering for one of the largest US boat builder and also, has a degree in chemistry?
Jacques Mertens - Designer"
http://bateau.com

I'm going with what the engineer & chemist says.

MD  

[damnitbadger]

Campbell, you never really stated what you were rebuilding on your boat. Most of the arguments posted have been debated on this and other forums. Bottom line is don't buy your resins from wally world type suppliers. US Composites http://www.shopmaninc.com/index.html or FGCI http://www.fgci.com/ . If you go with poly I would recommend the B-440 Premium Polyester Layup Resin from US Composites. I rebuilt the ass end of a 28' Luhrs with twin V8's that was fractured badly 6 years ago, gel coated,sealed primed and painted it and and it stays in the water to this day with no problems. If you decide on epoxy I have used both US Composites thick and thin resins for various repairs and layup. Both of these suppliers are large volume dealers and stock fresh materials. Do your homework before deciding which is best for your application. You will find a wealth of info both here and over at ClassicMako.com .

[dbiscayne]

heres my take on it- I've replaced the decks of three different boats, all over 20 feet long, one of those being a complete stringer rebuild & additional glass on the hull front to back.  Not saying I have a lot of experience just throwing that out there.  Used wood for the deck core nothing fancy.  Stringers were all glass over a foam mold.  One rebuild was with poly resin, the other two with epoxy.

Polyester Resin is cheaper, but here in S Fla where it's hot most of the time the poly resin kicks off really quick and I don't have a temp controlled work area always outside, I ended up wasting at least 15% of the resin by the time I was finished because it jelled up or hardened before I could use it all.
Epoxy is very consistent & easier to get the mix ratio right, definitely has a longer working time, but at the same time it's a little harder to work into the glass but I still get more done with it vs poly.  Shop around & you'll be surprised at how affordable epoxy can be.

Poly also doesn't stick as well as someone else mentioned.  It does work fine as long as you prep the surface good, but it'll never stick as good as epoxy, and I think epoxy is more foregiving?  If I'm covering wood I use epoxy.  Have done my own little experiments & the epoxy will pull the layers of plywood apart before it loses it's bond.  I cut a hole in an wood deck I built in 1995 to install a hatch and the wood looked brand new other than a little discoloration on the bottom side, it had been covered with thinned epoxy then two layers of bi-ax glass on top and straight epoxy on the bottom side.

Poly has a really strong odor, your neighbors will know you're up to something.  Epoxy not much at all.

I've been buying epoxy resin from Glue Products for a long time, always good fresh resin & the cost is somewhere around $35/gallon.  For all the reasons above I spend the extra money on epoxy now & I'm pretty cheap.  If Iwas building a lot of boats & had an air conditioned warehouse then poly might be worth it but for a one time build I'd recommend epoxy.