How to secure transom to exterior fiberglass skin

[paulbur]

I have removed the old transom, cut a new one and have coated it with epoxy on all sides. I tried gluing it with PL Premium and clamping it but it is still pulling apart. What should I be using to secure the transom to the exterior fiberglass skin??

[fireman24mn]

when you say you coated it with Epoxy do you mean paint or resin?

[75starflight]

That was my question too.

Don't glue it with PL! you must use fiberglass and resin to make the bond and a lot of clamps! The way I do mine, I lay down a fresh layer of resin on both the transom and the wood mating surfaces. Then I put down a layer of fiber glass on each and then apply more resin to wet the glass. then I line it up and clamp it together and let it set for at least a minimum of 48 hours or longer depending on air temp.

[Rich_V174SS]

If you've used epoxy then you'll have to grind it all off for polyester resin to adhere. Polyester resin won't bond to a surface that has had epoxy prior. The mating surfaces need to be roughened with a grinder and/or course sandpaper so fibers are showing. This provides a surface which new resin can bond to. When clamping it together you have to back up the outside with flat boards or 2x4's to make sure the fiberglass skin bonds flat and tight against the transom wood. Extra resin will fill spaces and squish out from between when it's squeezed together.

When I replaced a partial transom on my boat:

[75starflight]

Thanks Rich, I forgot that the surfaces need to be rough sanded.

[paulbur]

To answer your question: I used resin on the transom, not paint.

From what I've read from your posts I have to:
1) Remove the PL with a grinder to remove all foreign material
2) Rough sand the one side of the transom
3) Put a coat of resin on the transom and the wood matted surface
4) Put a layer of fiberglass mesh on both surfaces
5) Put more resin on both surfaces and then clamp..leave for 48 hours

Did I get that all right? Thanks everyone!

[Rich_V174SS]

Pretty much, but rough sand both mating surfaces for better adhesion. You mentioned in your original post you were using epoxy. There's a difference between epoxy and polyester, they're not the same thing. If you intend to go with polyester resin instead of epoxy you need to grind through all remnants of old epoxy. When I did my transoms I used polyester "laminating" resin which is thicker to make application on vertical surfaces easier and it takes longer to set up so there's plenty of working time. I let my transom set up for a week before removing the clamps.

Another one I worked on last summer:

[paulbur]

Hi Rich,

Thanks, I've been using West System epoxy in all my applications so far. Would you recommend the polyester resin instead? Any recommended brands to use for the polyester?

Paul

[Rich_V174SS]

You can continue to use epoxy, I only recommend a polyester laminating resin for bonding the transom together. I prefer polyester because that's what the boat was originally built with. But you have to follow the rule - epoxy will bond to cured polyester, BUT, polyester will not bond to cured epoxy. So, in any case where polyester is to be used the surfaces must be ground to fresh fibrous glass for bonding to occur. Evercoat has a laminating resin that comes in a quart can, should be plenty for the transom.

[V153]

I'd scuff it up real good and squish a pourable 'ceramic' compound in between. Once it kicks you ain't never gettin it out.

[Jerry]

I think the place to start is you never use Epoxy on a fiberglass boat. Polyester (that's what boats are made of) won't stick to it. It's chemistry.

[carlsoncvx18]

Jerry

I tend to disagree that epoxy will not work. 

I repaired have 18 with the west system which involved stringer and floor held up well.

And epoxy is stronger that any of the fiberglass  resins.

[V153]

Plus polyester's cheaper'n epoxy ...!

But seriously. Gotta side with Jerry on this one.

Granpappy Jack always said it was taboo to mix the two ...

[carlsoncvx18]

I agree with the cost thing.

But it is like putting latex paint over oil, you cant put oil over latex.

Everybody has there way of doing things, but epoxy worked for me and it can be done.

[Jerry]

If you don't think the factory made it strong enough, you can use Vinyl-ester resin that uses the same solids as Epoxy and is just as strong. Vinyl and poly can be mixed to give you whatever strength you want. I use Vinyl-ester to thin Bondo for bedding. West System has screwed up more boats because Epoxy is what they make Epoxy is for wood boats It will stick to poly great, but poly won't stick to Epoxy, and almost everything like bondo, and gel-coat are polyester. Sorry it's all about chemistry.

[V153]

All's we did in chemistry class was steal chit to construct bongs & water pipes and such. That and pilfer the occasional triple beam scale ...

But none of that's important now.

Combine epoxy and polyester at your own risk!