Adding fiberglass to fiberglass

[cjrenick]

I have a FG seat that I need to add to. Is there any issue with that? I think it has filler on it, seat is from slipstream, should I sand that out first? I need to fill the gap between seat and rear tank mount.

 

[VonYinzer]

Make a "mold" and go to town. You will want to remove the primer top coat so the new glass can bond to the old.

 

[cjrenick]

I was also thinking of making a seat pan that would go over the tank mount.

 

[Sonreir]

And you'll get much better adhesion and strength if you spring the few extra dollars for epoxy-style resin. If it doesn't say epoxy on the tin, it's probably Polyester resin, which is not the preferred choice in this application.

 

[J-Rod10]

If it came directly from me, there is no filler. Gelcoat and glass.

Also, gel is a poly, epoxy will not properly bond with it, and is overkill in that application.

 

[cjrenick]

The more I look at it and think about, it probably would be best just to do a seat pan and cover. Not sure I can get it to look right by adding FG.

 

[J-Rod10]

You could notch out a bit of the seating area, where the outsides wrap around.

 

[Sonreir]

If it came directly from me, there is no filler. Gelcoat and glass.

Also, gel is a poly, epoxy will not properly bond with it, and is overkill in that application.

Yeah... actually it will. Epoxy bonds with damn near everything. That's why JB Weld works so well at sticking two things together.

 

[J-Rod10]

Give Fibreglast a ring, ask them, or US Composites. It doesn't properly bond to gelcoat.

 

[Sonreir]

I believe you have it backwards. Epoxy will bond to gelcoat, but gelcoat may not bond as well to epoxy.

From the US Composites website:

[quote author="Epoxy FAQ"]7. What are the advantages of epoxy over polyester resins?

There are many advantages including being non-flammable, not exhibiting a strong odor and being up to 25% stronger than their polyester counterparts. In marine applications, epoxies are far superior in resisting water absorption and are less likely to blister. Epoxies are more flexible and adhere better to all surfaces.[/quote]

 

[jsharpphoto]

whether or not epoxy will bond to gel coat is kind of irrelevant, because the original poster should sand off the gelcoat to get to the bare weave, right?

 

[Sonreir]

Yeah, but perhaps for different reasons than are immediately apparent.

You sand it down so that you have low spots to which you can add more glass and resin (of whatever type). Then when you sand the finish product flat you're not sanding off everything you just added and creating weak spots.

 

[jsharpphoto]

What about drilling two rows (offset from eachother) on the original part for a mechanical AND chemical bond?

This isn't my thread, sorry. Just trying to help.

 

[shoom]

I used to work at a boatbuilding factory and believe me epoxy will bond to polyester (fibreglass) , it just won't work the other way around, ie polyester resin won't bond to epoxy. And you can't use epoxy with chopped strand mat, only the cloth stuff as epoxy doesn't have the styrenes in it to break down the glues that hold the strands together on CSM. But in any case, I would get a DA sander or sanding pad on an angle grinder and sand back the gelcoat to the laminate whereever you are going to be bonding, to ensure a proper key.