On Wed, 9 Dec 2009 20:55:09 -0800 (PST), the infamous
" scrawled the following:

Has anyone had experience with a water protective finish for MDF? I
have a work table with an MDF top, and I briefly set a glass of ice
tea on it, and the wet spot swelled up. Fortunately, it wasn’t
permanent. I saw that Pat Warner saturated his router table top with
Watco. I wonder how that worked out.

I have on hand Watco, Exterior Watco, Waterlox, and several types of
varnishes. What would be best? I plan to submerge the top, but I don’t
want water soaking in on contact.

I've always loved Waterlox, so I'd use that: 10 handrubbed coats or 4
brushed coats. I much prefer handrubbed to brushed. Use 420 grit
between coats if you feel any roughness at all. I handrub two coats
the first day, then go to one coat a day at quickest. I really like
drying time, even with quick-drying products like Waterlox. More
screwed-up finishes have been had from hurrying. None from waiting.

I would let that ring dry out WELL before you sand it and seal it.
Otherwise, once it does finally dry out, you'll have a ring dip in the
tabletop. A light bulb about 8" off the surface should dry it out in
a couple days. Let it cool well before starting, and even though it's
not real wood, use a quick wipedown with lacquer thinner or mineral
spirits before putting the finish on half an hour later. Again, I wait
for the thinner to be completely gone before I start work.

Oh, wait, you said you plan to _submerge_ the top. Forget using MDF
for that, -ever-. Any pinhole leak will blow the thing out in 5
minutes.

--
To know what you prefer instead of humbly saying Amen
to what the world tells you you ought to prefer,
is to have kept your soul alive.
-- Robert Louis Stevenson