Yes, you can do so. There’s nothing that stops the two from bonding as long as you provide the right environment for it. More in this in this guide and how to make sure the epoxy stays on.
Pouring Epoxy Over Oil-Based Poly
Some want to apply epoxy on existing polyurethane surfaces to achieve a more durable coating.
This is unusual because epoxy is used primarily as an adhesive in woodwork and not for finishing. Poly on the other hand is used for providing a beautiful finishing.
The formulation of epoxy is harder than polyurethane, which is why you may want to use it on poly.
This is not a practice by most people as the result is not as attractive as when you apply only polyurethane. If you wish to pour epoxy over poly however, you need to do it right to get it right.
How To Pour Epoxy Over Oil-Based Poly
Oil based poly has a glossy finish which is one reason some people prefer it to water based polyurethane. For this reason, if you want to pour epoxy over it you have to do this:
- Get a sandpaper, preferably, a 320 grit
- Get a sanding block and wrap the sandpaper around it
- Lightly run the block over the surface of the polyurethane. Check the surface after every stroke to make sure you are not rubbing too hard
- Clean the residue of poly off the surface
- Apply your epoxy slowly on the surface
The secret is creating sufficient grip on the surface of the rather slippery poly finish.
Nothing special is expected of you to get epoxy on poly other than preparing the surface. It is the same as when you apply polyurethane on the wood. Epoxy is thicker, so be sure to apply a little at a time. Aim at getting an even coat.