On Oct 24, 2:19*pm, Mark
wrote:
On Tue, 23 Oct 2012 19:32:23 +0100, Roger Mills
wrote:

On 23/10/2012 17:47, polygonum wrote:

Completely agree that they can raise the grain. But, in that sense
luckily for me, most of my painting is re-decorating where the substrate
is already pretty well covered.

I find that water-based paint is fine on wooden door frames and
skirtings, etc. However, what it's *not* fine on is MDF window cills if
they're ever likely to get wet. When the paint is thoroughly dry it will
still let water through - unlike oil-based paint - and this will bring
the MDF up in a nasty rash.

I wouldn't use MDF for window cills again. *They all turned into
Weetabix, even using oil-based paint.

I think you were using chipboard. MDF delaminates; it's more like
sheets of Shreddies.