Poly/Epoxy Compatability Question(s)

[micks110]

I have been doing my entire hull with polyester resin up to this point.
http://forums.iboats.com/showthread.php?t=365820

My question is when I get to installing my deck is should I use epoxy for my fiberglass that I put on the top of the deck and underside that you will never see. Or just stick with using poly?

Another question is will epoxy and polyester work together. For instance- I'm using poly for stringers and such- before I screw my deck down to my stringers should I put epoxy like the six-10 in the pre-drilled holes or poly? I guess the same goes for the holes I will be putting in the transom for my engine mounts and ski hook ups.

I have been reading alot of different ideas on my topics but I figured I'd just ask in a new thread

Thanks

 

[Bondo]

Re: Poly/Epoxy Compatability Question(s)

Or just stick with using poly?

Ayuh,... I'd stick with it,... Epoxy don't like sunlight...

Using it to bed screws won't hurt,.. They'll Never come out...

 

[micks110]

Re: Poly/Epoxy Compatability Question(s)

Thank You Bond-o

 

[drewpster]

Re: Poly/Epoxy Compatability Question(s)

I agree with Bond-O. I normally use epoxy for applications where I wont be using any cloth at all.

 

[erikgreen]

Re: Poly/Epoxy Compatability Question(s)

I agree with Bond-O. I normally use epoxy for applications where I wont be using any cloth at all.

?? Explain, please



Generally for compatibility, remember that poly won't stick to epoxy. The reverse is not true.

In short, once you commit to using epoxy you can't go back to poly later without some trouble.

If you've used poly for structural work up to now, keep using it for the non structural work and you'll be fine.

Erik

 

[drewpster]

Re: Poly/Epoxy Compatability Question(s)

Quote:
Originally Posted by drewpster
I agree with Bond-O. I normally use epoxy for applications where I wont be using any cloth at all.

?? Explain, please by erikgreen

In my opinion epoxy works best for bonding and finishing on substrate that is going to be painted. I would not use epoxy on finishing applications where the top coat is going to be gelcoat. As you pointed out, gelcoat, a polyester product, does not bond well to epoxy.
In my opinion epoxy is overkill for major structural work. However epoxy is great for finishing fillers, blister repair or bonding parts together. In most of these cases you do not need cloth reinforcement. (with a few exceptions)
Some restorers prefer epoxy because of its superior strength and bonding capabilities. It also possible to build stronger, lighter parts using epoxy. But for me the cost of epoxy outweighs its benefits in major structures.

The point is this- If you have the money to rebuild a boat using marine epoxy, you probably have the money to buy a new one.

 

[erikgreen]

Re: Poly/Epoxy Compatability Question(s)

Quote:
Originally Posted by drewpster
I agree with Bond-O. I normally use epoxy for applications where I wont be using any cloth at all.

?? Explain, please by erikgreen

In my opinion epoxy works best for bonding and finishing on substrate that is going to be painted. I would not use epoxy on finishing applications
[snip]
The point is this- If you have the money to rebuild a boat using marine epoxy, you probably have the money to buy a new one.

Heh, very much not true in my case. The way I buy epoxy it only costs me about $20 more a gallon than poly, and it's worth it to get strength, weight savings, etc. Unless I'm molding items I only ever use epoxy.

Interesting point of view on uses for epoxy, that does explain the "not cloth" bit......

Erik

 

[MTribe08]

Re: Poly/Epoxy Compatability Question(s)

Heh, very much not true in my case. The way I buy epoxy it only costs me about $20 more a gallon than poly, and it's worth it to get strength, weight savings, etc. Unless I'm molding items I only ever use epoxy.

Interesting point of view on uses for epoxy, that does explain the "not cloth" bit......

Erik

So if one was going be replacing a portion of the deck that had rotted out and bonding a new piece to the portion not affected, would it be better to use Epoxy with cloth for the new panel and seems?

 

[drewpster]

Re: Poly/Epoxy Compatability Question(s)

So if one was going be replacing a portion of the deck that had rotted out and bonding a new piece to the portion not affected, would it be better to use Epoxy with cloth for the new panel and seems?

Yes, epoxy would work great for that. Just remember that polyester gelcoat does not bond well to epoxy substrate. So plan to finish it using another kind of process like paint or possibly pigmented epoxy. As Bond-O mentioned above epoxy does not like sunlight. The UV will break it down over time. Leaving it uncovered is not a good idea. You would not want to leave polyester unfinished either.

I think erikgreen and I agree that marine epoxy resin is superior to polyester resin in many ways. However that fact does not preclude the use of polyester in many repairs. Professionals have been using polyester resin for years to do repair work. For me it comes down to what my wallet dictates. "Only $20 more a gallon" is still almost double the cost of polyester. For a minor repair like your deck portion it would be great. But for doing every core in the boat? My accountant (wife) would have a fit!

 

[system-f]

Re: Poly/Epoxy Compatability Question(s)

"Only $20 more a gallon"

This is double the cost of poly in my area.

 

[erikgreen]

Re: Poly/Epoxy Compatability Question(s)

I suppose we could start a poll on epoxy vs. poly cost in different areas.

But everyone can order online if they're posting on this board, and generally that's cheapest anyway.

At US Composites, costs are:

5 gallons standard poly layup resin: $121 or $24.20/gallon

5 gallons vinyl ester resin: $171 or $34.20/gallon

6.6 gallons 635 epoxy resin: $243 or $36.81/gallon

So per gallon it's about a $12 difference from them. Shipping on the 6.6 gallon order usually comes to about $40 ups ground, so that's about $6 a gallon no matter the type of resin (5 gallons is less weight, true, but doesn't cost significantly less).

So I can order US Composites epoxy, which is always fine quality stuff, for about $43 a gallon delivered.

Alternatively I can get US Composites poly for $31 a gallon delivered

I can get generic marine poly locally in 5 gallon lots for about $25 a gallon plus cost of MEKP.

Or I can buy Bond-o poly locally for about $30 a gallon at Home Depot.

Kind of an apples to apples comparison, since I wouldn't use the Bondo resin for my boats... too thick, off color, etc.

For me that price difference is minimal. Plus there are other benefits I like... eg. no mat required so glassing is faster, longer working time, less fumes, etc.

What's your local price for a gallon of poly resin compared to the US Composites price of $43 a gallon delivered? How much are you saving?

And given how much time and money you're spending on your boat repair otherwise, isn't the money a good investment?

Erik

 

[system-f]

Re: Poly/Epoxy Compatability Question(s)

Don't forget the $20 / 5 gallon hazard fee with the poly resin you don't have to pay on epoxy I would love to use epoxy, but poly is just too accessible now that I found a local supply.