Varnishing raw MDF

[Jon Parker]

Can it be done?

Or must it be sealed first? Sealing presumably is done with some pva/ water mixture?

Cheers for any advice.

Jon

[The Natural Philosopher]

Can be done. You will need to rub down and use many coats on the edges though.

Which then seals it ;-)

[Andy Dingley]

Yes. I do this regularly for workshop jigs, to avoid them swelling from damp.

Two primers work for MDF: either dedicated MDF primer or shellac. If you use anything water based instead, including PVA, you get swelling of the fibres. This makes the edges swell, or raises odd fibres on the surface. Shellac is cheap, quick and works well.

Edges take three coats before you even notice it's there.

[Spamlet]

Yuk! Varnish on PVA! General principle: *always match like with like*.

Varnish is an excellent sealer (PVA is just cheap) - but use the 'diamond hard' (or indeed shellac itself or similar hard resin) or it will always be tacky. Incidentally, even chipboard polishes up nice and varnishes effectively if you have the patience to sand it carefully down through the grades.

S