You should be able to do it, but I would stick to oil based if you started with that. I have never been fond of the Water Based Poly.

If it has oil based poly on now, use oil base. Water base will more than likely fail or chip off if you hit the surface with something.

Thanks - I knew that was the answer but was hoping I could get away with it. ;-)

And now that I am ready to varnish of course the weather is not cooperating - too much rain or too cold to varnish outside, or even varnish inside and open the windows. Oh well, I've only been waiting since November for these shelves to be finished. I can wait a little longer.

Thank you again!