On Sun, 09 Apr 2006 15:19:49 +0100, Mike Halmarack ... wrote:

I hope you're wrong. I have great hopes of putting a newly painted
corner unit made from MDF into my bathroom. I'm counting on several
coats of paint to protect it from moisture.

It will last as long as the paint remains impermeable. Then it will turn
into cheese. You can certainly do this, but I'd be wary of it.

A much better material is Valchromat - MDF with extra resin content,
making it both water-resistant and also pre-coloured.
http://codesmiths.com/shed/furniture/cabinets/swarf/

I'd be amazed if an MDF outdoor sill lasted more than a winter or two.