ok now I'm confused! stupid fiberglass!!

[chumslinger]

after reading too many threads on fiberglass, i am getting more confused the more i read..ok so now my question...why can you put epoxy over poly, but not poly over epoxy? it would seem to me that either way it is still poly against epoxy.....now this is assuming the base layer has fully cured, then properly cleaned...am i missing something, cause i thought if the base layer is fully cured, any other layers added afterwards would only have a mechanical bond. maybe some of our resident experts here could explain this to a simplton such as myself thanks....nate

 

[ondarvr]

Re: ok now I'm confused! stupid fiberglass!!

Epoxy is a very good glue and sticks well to most surfaces, polyester sticks very well to anything you spill it on, but not as well if you want to use it as a glue. The chemistry is very different between the two, so the glue (epoxy) sticks well to polyester like it should, the polyester will stick to epoxy as long the bond isn't stressed too much. If it gets banged or stressed it can chip off easily and the bond surface of the polyester will be a perfect mold surface of the sanded epoxy.

 

[lowkee]

Re: ok now I'm confused! stupid fiberglass!!

I've wondered this same thing, and just assumed the answer was: It will work both ways, but poly needs a rough surface as it uses a mechanical bond, as opposed to epoxy's chemical bond. So, assuming I am correct in that statement, poly (or gelcoat) will work over epoxy, but only if you rough it up beforehand.

Hopefully someone can agree or disagree with that statement and we can both stop being confused.

 

[chumslinger]

Re: ok now I'm confused! stupid fiberglass!!

ok now i have a second question to add here....if poly is half the price of epoxy, but reqires more cloth, mat, resin use, wouldnt the price almost be the same to use epoxy? and if so, with all the advantages of epoxy, why do so many people use poly on boat rebuilds? feel free to explain as if i know NOTHING about this because in reality, thats about all i really know
thanks.....nate

 

[jonesg]

Re: ok now I'm confused! stupid fiberglass!!

I don't use more mat with poly,
I like the lower initial price of poly,
I don't like enviromental shipping chgs so I buy it local.
I like the faster cure time of poly.

I don't really care what the molecular reason is for what doesn't work over what , as long as I stick with polyester I don't need to know more than I do, which ain't much... but it works for me.

 

[keepNitreel]

Re: ok now I'm confused! stupid fiberglass!!

ok now i have a second question to add here....if poly is half the price of epoxy, but reqires more cloth, mat, resin use, wouldnt the price almost be the same to use epoxy? and if so, with all the advantages of epoxy, why do so many people use poly on boat rebuilds? feel free to explain as if i know NOTHING about this because in reality, thats about all i really know
thanks.....nate

I was in West Marine yesterday and seen a gallon of epoxy resin priced @ $84 and the hardener for it was $64, that's $148 for a gallon worth of resin . I can order a 5 gallon pail of Poly resin from US Composites for $121 + $20 environmental shipping chg + regular shipping chg $25.50 = $166.50 and have 4 gallons more for $18.50. Now US Composites sells there epoxy in 5 gallon pails for $240 and there is no environmental shipping chg for epoxy just regular shipping $25.50 = $265.50. Here it's only a $99 difference but $100 is a $100. If I was repairing a 2008 boat I would probably use epoxy but for a 1967 runabout, poly is good enough

 

[metriccrescentwrench]

Re: ok now I'm confused! stupid fiberglass!!

if poly is half the price of epoxy, but reqires more cloth...

For the most part a given structure would require the same amount of fiberglass no matter what resin you use. The strength is in the fibers, resin just holds it together.

 

[ondarvr]

Re: ok now I'm confused! stupid fiberglass!!

I've wondered this same thing, and just assumed the answer was: It will work both ways, but poly needs a rough surface as it uses a mechanical bond, as opposed to epoxy's chemical bond. So, assuming I am correct in that statement, poly (or gelcoat) will work over epoxy, but only if you rough it up beforehand.

Hopefully someone can agree or disagree with that statement and we can both stop being confused.

There is no chemical bond between the two going either direction and both benefit from a well sanded and clean surface. Polyester is a very good substrate for bonding to, most glues, paints, resins, etc, stick to it very well without primers. Epoxy is just one of those things that polyester doesn't really like to stick to long term.

 

[TK]

Re: ok now I'm confused! stupid fiberglass!!

I was in West Marine yesterday and seen a gallon of epoxy resin priced @ $84 and the hardener for it was $64, that's $148 for a gallon worth of resin . I can order a 5 gallon pail of Poly resin from US Composites for $121 + $20 environmental shipping chg + regular shipping chg $25.50 = $166.50 and have 4 gallons more for $18.50. Now US Composites sells there epoxy in 5 gallon pails for $240 and there is no environmental shipping chg for epoxy just regular shipping $25.50 = $265.50. Here it's only a $99 difference but $100 is a $100. If I was repairing a 2008 boat I would probably use epoxy but for a 1967 runabout, poly is good enough

It depends where you live and where you shop.

I get epoxy resin for $47.00/gal. and Hardener for 57.00/gal. I can pick up or they will drop it off for $3.00.

 

[cheesegrits]

Re: ok now I'm confused! stupid fiberglass!!

Check out www.boatbuildercentral.com they have several choices of resin. I have always used their marinepoxy and had really good results. My decision to use epoxy is based on secondary bonding and my nose! The styrene smell is really strong with polyester and it will fumigate your entire house totally pissing off your better half. Most epoxys don't smell too much. On BBCs site they have several video links that are extremely helpful with terminolgy and use of products. My.02

 

[keepNitreel]

Re: ok now I'm confused! stupid fiberglass!!

It depends where you live and where you shop.

I get epoxy resin for $47.00/gal. and Hardener for 57.00/gal. I can pick up or they will drop it off for $3.00.

Yeah, that's pretty expensive still compared to poly resin. your price for epoxy = $104 dollars.

Now my question is, since it is a gallon of each will it make 2 gallons of workable resin for use?

 

[TK]

Re: ok now I'm confused! stupid fiberglass!!

Yeah, that's pretty expensive still compared to poly resin. your price for epoxy = $104 dollars.

Now my question is, since it is a gallon of each will it make 2 gallons of workable resin for use?

You make a good point...except I should of been more precise. The epoxy I buy is a 3.1 ratio. So each usable gallon only costs $66.00 .

The price difference is much less.

 

[chumslinger]

Re: ok now I'm confused! stupid fiberglass!!

thank you all for your replies! before i start a big expensive project, i like to get as much info i can. keep the comments comming!
thanks....nate

 

[chumslinger]

Re: ok now I'm confused! stupid fiberglass!!

For the most part a given structure would require the same amount of fiberglass no matter what resin you use. The strength is in the fibers, resin just holds it together.

somewhere i read epoxy is stronger than poly, requiring less glass/resin for the sasme strenght.....not disagreeing, just too much time thinking.......

 

[redfury]

Re: ok now I'm confused! stupid fiberglass!!

Epoxy by itself is strong. Polyester or Vinylester is not. I bet if you wanted to wait, you could use polyurethane and fiberglass and get a decent end product...the dry/cure time would kill ya.


In the end, essentially you are strengthening the epoxy with the fiberglass, you are strengthening the fiberglass with the polyester.

 

[lucid484]

Re: ok now I'm confused! stupid fiberglass!!

woa..reading all these posts is getting me more confused by the day!!! I have to rebuild my transom,redo the stringers,redo a deck and reinforce the gunwales to keep them from flexing.....so what the hell kind of resins do I use and where do I use them!!!!

 

[ondarvr]

Re: ok now I'm confused! stupid fiberglass!!

Just pick one resin or the other, the final product won't be any different.

 

[drewpster]

Re: ok now I'm confused! stupid fiberglass!!

For me it is all about the cost. By the time I am finished with the structural part of my tri-hull resto I will have around $1200-$1500 in materials. (sloppy guess, but certainly no more) If I went with all epoxy to do the job, even with a reduced cost in fiberglass, the price would be at least a third higher. And frankly, it is not necessary. Epoxy resins are great products. I have used them, and they are superior to poly resin in many ways. But why spend the money when Polyester will do the job I want it to do? The boat was built using polyester resin. It lasted 30 years before the work I am doing became necessary. If I get 10 more years out of her, my job is done. Even my sloppy work should last that long!

 

[legoman67]

Re: ok now I'm confused! stupid fiberglass!!

theres a 99% chance that your boat is built with poly resin, so the way i see it, there is really no point in using epoxy unless you are really lazy and dont want to do the prep work(sanding, acetone, etc) We have a local shop that sells poly resin for 39.00 a gallon, and 250ml of hardener for 15.00. We spent the time sanding and cleaning(an hour at most even for our large transom) and everything worked out great! there isnt really a reason to use expoxy resin on normal fibreglass boat repairs.

what epoxy is good for is autobody repairs(plastic body parts) that with some 1708 cloth that was leftover and my body kit aint going to break anytime soon