will epoxy bond with gelcoat?

lime4x4

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I sanded the bottom paint off the stern down to the gelcoat.I want to bond 2 strips of plywood to the bottom of the transom for mounting lites and my depth finder. This way i don't have to drill any holes into the transom below the water line
 

Shife

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Re: will epoxy bond with gelcoat?

Epoxy will secondary bond with cured gelcoat. Make sure to rough the surface up so the epoxy has something to key into.
 

erikgreen

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Re: will epoxy bond with gelcoat?

Note also that the bond to the gelcoat will be good, but it will limit the strength of the attachment of whatever you're gluing/laminating on to the strength of the gelcoat bond to the underlying glass, which is typically much weaker than the bond epoxy makes with the same material.

This is why most people who want a strong bond using epoxy (and otherwise why not just use poly?) grind off gelcoat from laminating surfaces.

Erik
 

lime4x4

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Re: will epoxy bond with gelcoat?

In the picture below u can get a rough idea where i want to bond the 3/4 plywood to the bottom of the transom plate. The wood is only going to be used for mounting underwater lites and a depth finder transducer

0404001038.resized.jpg
 

avimgod

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Re: will epoxy bond with gelcoat?

Why not just drill the holes, and use 5200 to seal everything back to the transom when installing the screws.. That is how my transducer, trim tabs and wires back there are all done with no issues...
 

lime4x4

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Re: will epoxy bond with gelcoat?

When i sanded the paint off. On the port side there were atleast 25 different holes drilled into the transom over the years
 

ezmobee

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Re: will epoxy bond with gelcoat?

May I recommend a piece of that PVC trim board they sell at Lowes as opposed to plywood? Won't ever rot.
 

Bob_VT

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Re: will epoxy bond with gelcoat?

I would still drill and use some SS screws and a layer of 5200 or equivalent. That board is going to need real bite to stay in place and if the board tears off under way it will tear up the wires of anything connected.
 

Shife

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Re: will epoxy bond with gelcoat?

Screws and 5200 will just lead to a soggy transom down the road IMHO. If you're going to use hardware, drill oversize, thickened high density epoxy plug, and then drill and through bolt through the epoxy plug. Use a quality soft bedding compound such as Dolfinite to prevent water seepage along the bolt shank. The transom core is then isolated from any chance of moisture intrusion and the attached item is more securely assembled.

If access from the inside is limited the same can be achieved by using epoxy in a blind hole method to bed studs or nuts into the laminate without passing all the way through.
 

erikgreen

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Re: will epoxy bond with gelcoat?

I didn't read the original post (my bad) so the sanding off of the gelcoat isn't needed.

For this, as some have posted, I'd recommend a PVC board, or if you don't want to use them because of price or looks, you can use a piece of vinyl trim board the right size from your local big box home improvement store.

I'd recommend 5200 for attachment, plus two long stainless screws. The process for attachment should be:

1) Locate and mark the position of the board on the transom, including the screw holes. If the board has no holes, drill them first.

2) Overdrill the screw holes marked in the transom with a bit about 1/4" larger than the one you'd drill pilot holes with for your screws. Drill to the depth you'll need plus a bit, but avoid drilling through the transom.

3) Fill the holes flush with the transom with epoxy thickened with cabosil and milled fibers or wood flour.. cabosil alone will work in a pinch.

4) Once cured, you sand as needed to clean up the holes, which are now plugged flush with solid resin. Then you drill centered pilot holes in those plugs using a correctly sized bit.

5) Sand the back of the vinyl or pvc board a bit, or use another means to rough them up (follow the mfgr. directions for the PVC)

6) Apply 5200 around the edges of the board (back a bit from the edge, because it'll squeeze out) and place it in position on the transom. Hold it there while you thread the screws into the holes, then tighten the screws down all the way. Be prepared to wipe/catch any squeezed out 5200.

7) Use a popsicle stick to form fillets around the edges of the PVC board, and then clean up excess 5200 as the manufacturer directs.

8) You can start mounting right away if you like, but a day or so to start curing of the 5200 avoids messes. Make sure you mount with screws short enough to not fully penetrate the plastic board and make a hole in the transom.

Erik
 
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