Tying poly and epoxy repair areas together

[sbklf]

I used epoxy below the deck, up the sides and over the gunnels for structural repairs on my boat. I then used polyester resin on the top side (deck). Now I have to tie the two together (at the deck/side wall intersection). I know that epoxy bonds to poly and not the other way around so I poly'ed the deck to within 3" of the side and plan to epoxy that 3" and then another layer overlapping the poly to tie them together. Will this work?

How long do I need to wait before applying the epoxy over the poly to get a good mechanical bond?

I have decided to Gelcote the deck rather than using polyurethane paint. What do I have to do to the epoxy areas to get the Gelcote to adhear to it?

If I ever, do this again, I will reconsider materials to use. Epoxy sounded like a good idea at the time.

 

[ondarvr]

Re: Tying poly and epoxy repair areas together

Let the polyester cure, then sand it thoroughly and the epoxy will stick great. You'll be better of painting over the epoxy, it can be too difficult to get a good bond with gel coat over epoxy.

 

[Old Salt Oz]

Re: Tying poly and epoxy repair areas together

G'day sbklf,



Quote:
<<<I have decided to Gelcote the deck rather than using polyurethane paint. What do I have to do to the epoxy areas to get the Gelcote to adhear to it?>>>

Do you mean 'Flow coat' the deck, Adding gel coat will not be easy over a large area and would have to be epoxy based to get a good enough bond.

Quote:
<<<If I ever, do this again, I will reconsider materials to use. Epoxy sounded like a good idea at the time.>>>

Epoxy would be the only way to go in most repair situations due to the better bonding of epoxy over poly resins, up to 40% stronger.
Trying to bond poly to poly after only 8 weeks of curing can be a problem to.

Poly resin over poly resin is fine for things like pads under the deck to reinforce it as the material only needs to hold and protect the pad, the through bolts will hold it in place so the resin is under compression not tension so no problem.

I hope this helps.

Avagoodweekend......

 

[Chris1956]

Re: Tying poly and epoxy repair areas together

Epoxy and Poly resins bond to each other quite well in any sequence, provided the surface is fully cured, well sanded and wiped with acetone.

The folks who disagree with this operate in ignorance or lack of experience or technique.

 

[BillP]

Re: Tying poly and epoxy repair areas together

G'day sbklf,



Quote:
<<<I have decided to Gelcote the deck rather than using polyurethane paint. What do I have to do to the epoxy areas to get the Gelcote to adhear to it?>>>

Do you mean 'Flow coat' the deck, Adding gel coat will not be easy over a large area and would have to be epoxy based to get a good enough bond.

Quote:
<<<If I ever, do this again, I will reconsider materials to use. Epoxy sounded like a good idea at the time.>>>

Epoxy would be the only way to go in most repair situations due to the better bonding of epoxy over poly resins, up to 40% stronger.
Trying to bond poly to poly after only 8 weeks of curing can be a problem to.

Poly resin over poly resin is fine for things like pads under the deck to reinforce it as the material only needs to hold and protect the pad, the through bolts will hold it in place so the resin is under compression not tension so no problem.

I hope this helps.

Avagoodweekend......

Can you elaborate about the "bonding poly to poly after only 8 weeks of curing can be a problem" statement?

bp

 

[sbklf]

Re: Tying poly and epoxy repair areas together

Epoxy and Poly resins bond to each other quite well in any sequence, provided the surface is fully cured, well sanded and wiped with acetone.

The folks who disagree with this operate in ignorance or lack of experience or technique.

I plan to prep the epoxy areas considering the advise I have received and gelcoat it. Does anyone know how much I can speed up the cure time on epoxy with heat lamps so I can get this done?

 

[ondarvr]

Re: Tying poly and epoxy repair areas together

As a supplier of polyester resin and gel coat I would not recommend using it over epoxy and no other resin or gel coat supplier will either. You used epoxy in the begining because you wanted the better physical properties it can provide, and bonding is one of those properties you wanted. Now you want to use gel coat over it, which typically results in a very poor bond to epoxy. If done carefully and correctly, it will sort of bond, but not great and it's not that reliable, that's why it's not recommended.

 

[BillP]

Re: Tying poly and epoxy repair areas together

Ditto on what ondarvar says, the whole industry is and always been anti poly over epoxy. WEST seems to be the only big name company who says poly is ok over epoxy but they don't make the resin they sell either. They did a one shot short term empiracle test as a reference for their opinion. They also say pressure treated wood doesn't work...which is opinion opposite to it's proven success in the industry for the last 20+ yrs.

bp