Bonding Polyester to Epoxy - Will this Work

[76SeaRay]

So, originally I planned to use epoxy for all my stringer work but the budget doesn't allow that. I got to thinking about using epoxy to just bed the stringers in peanut butter and then polyester to glass them in. My question is this, if I glass in the stringers while the epoxy peanut butter is still not quite cured (slow hardener), would the polyester (tabbing) be bonded to the epoxy (fillet) as they both continue curing or is this just a really bad idea?

 

[froggy1150]

Bad idea and a waste of epoxy. Bedding is to eliminate hard spots and the real strenght is from the layers of tabbing.

 

[Chris1956]

Polyester resin will bond just fine to sanded, acetone-cleaned epoxy.

Froggy is probably right that you do not need to use epoxy. Your boat was originally made from all polyester resin and cloth.

Epoxy is only necessary for high strength repairs. For example, I had a hole knocked into my speedboat hull at the waterline by a piling. I ground the hole to feather it, but was concerned about the cloth having enough surface area to bond.

I used 5 or so FG cloth patches, each a bit larger, on the outside to build back thickness, and a heavy piece of roving on the inside for added strength and fail-safe. I saturated all the cloth and roving with epoxy resin and applied it in monolithic fashion.

A lot of years and use later, I have no issues and the repair is invisible on the outside.

 

[todhunter]

Just do everything in poly. It's cheap, it's easy to work with, it cures faster so your project will move along faster, you can adjust the cure speed by how much catalyst you add, it's what your boat is already made of, it's what gelcoat is made of....the list of positives goes on.

 

[JASinIL2006]

I'd just use all polyester, too. Even a possibility of adherence problems between poly and epoxy would be enough to dissuade me from using epoxy. Why take a chance? Polyester will work fine, and then you don't need to worry about it sticking to epoxy. Probably less expensive, too.

 

[76SeaRay]

Polyester it is.. Thanks for the feedback.. By the way, I found an excellent example of the hard spot problem on the side on my hull.. The bulkhead between the V berth and the kitchen area at one point pushes against the side of the hull over about two to three inches.. Directly opposite on the outside of the hull is cracking in the gelcoat.. I will be removing the bulkhead anyway so I will reinforce that spot with a patch on the inside and making sure the new bulkhead doesn't press on the wall of the hull.. This shows that the hard spot problem can occur in the sidewalls and not just in the stringers.

 

[froggy1150]

I had to mix both. Previous repair done in epoxy,whole rear bilge and motor mount stringers. Tried to grind out but hull was getting thin so i wrapped everything in poly,bedded in epoxy. Tabbed in epoxy then i transitioned to poly by putting poly wrapped pieces glued down with epoxy. Tabbed the poly side of the transition then retabbed the epoxy side. If that makes sense