Cheap paint to seal and harden MDF surface?

[tonyroe]

I have an ongoing need (well, a desire anyway) to paint all the hidden unfinished surfaces of some MDF projects in the hope that it will slow or stop future moisture ingress, and also maybe harden the surface a little to boot.

I also happen to have bought some cheapo speaker boxes recently that seem to work OK now, but they're made of very low density particle board which looks like it would fall in a heap on the floor if I left it next to the bathroom door for a few hours, so especially anxious to coat all the surfaces of those.

I also use ply and solid wood, but I'm guessing their ends/edges are the only parts that need sealing.

I don't want to buy anything special - preferably just use something lying around - sealer, undercoat, primer, acrylic wall paint, enamel, etc - whatever might work best. Anyone tried this approach, of have any thoughts on it? Cheers, Tony

[Harry72]

Fibreglass resin or epoxy resin, mdf soaks it in readily and once set is almost water proof. Its great for the side/end grain as it glues all the fibres together enough that they can be polished glass smooth.