another epoxy question

i need to glue a piece of 1" ply on the inside of my transom. if i rough up the glass and give it a good wipe with acetone will epoxy take to it.

 

Use a very coarse grit, like 36 and really tooth up the inside of the transom. The acetone wipe isn't necessary, assuming the surface was clean when you sanded. Technically, you'll need to grind through the gel coat, but I wouldn't bother, just "tooth" it up good with a sander and seriously rough grit. Mix up a thickened batch of epoxy, using milled fibers and silica. Apply with a 1.5 to 3 mm notched trowel or spreader. Wedge or brace it into position with some scrap stock, just enough to get the epoxy to ooze out around the edges. You don't need a lot of pressure, just enough to make the insure good contact with the parts involved. Blend the ooze out onto the edge of the plywood, making a little fillet around the perimeter, especially on top, so it'll shed condensation.

I'm assuming this is a backing plate for a small outboard motor or it's bracket. The technique above works fine for up to 10 HP. If mounting more then this, grind through the gel coat until you've got mat everywhere in the contact area, then do as described above.

 

thanks for the great reply, i am converting from shaft drive to single stern drive. the transom is 3/4" solid glass, i want to fit the ply across the inside to build up the thickness. there is heaps of strength already there from 2 big stringers. i read that legs need 1 1/4" to 2" of thickness to bolt to. a silly question but what are milled fibers.

 

Log onto Westsystem.com and Systemthree.com and download their free "user's guides". These will nurse maid you through the basics, including materials for fillers.

Are you sure the current transom is solid 'glass, as 3/4" would be a hugely thick laminate for a straight shaft equipped boat. It's more likely you have two 'glass skins, with a plywood core in your transom.

In any case, the additional piece on the transom should also be under those big stringers. By this I mean you shouldn't notch the transom thickening plywood to fit, but the other way around. This is as simple as taking a reciprocating saw and lopping off the last 1" or so of those big stringers (engine bed logs?). The new transom piece installed behind it and then the whole shooting match is tabbed together with some biax and epoxy, over generous fillets of more milled fibers and silica.

What make, model and year is your boat? Can you post some photos?

 

it is solid glass. savage lancer around 1980 model 26' x 9' beam. these boats are way over built thats why the glass is so thick. i will try to find the pictures, it is the boat in my avatar.