Thread: Best coating for MDF?

What I've done in the past is using either shellac or poly in a weak kind of sanding sealer dilution with a couple of coats so it soaks right into the MDF faces without building up too much and making it "less straight" with uneven spots. If it has happened, some careful light sanding with high grit wet and dry paper backed with a large, flat, hard surface over the full length soon sorts it out.

Where the sides of the MDF aren't being used as straight edges (back, top, sides...*maybe* bottom), then you can apply a full strength finish to really stop the moisture getting in from those places.

If it gets hot in your shed go with the poly thinned with turps as the shellac can still warm up and get sticky.

Hi Jill
Just remember you live up here where it rains a LOT and is humid.
Instead of MDF, I used the white stuff (old timers disease ) they make cutting boards from.
It worked a treat and never moved with humidity, neither did it turn into weetbix when it got wet, the only thing in the router table YASI didn't destroy
Cheers
Wolffie

I'm about to finish a computer desk made of MDF and did a couple of test pieces using polyurethane (Wattyl UniPak - cheap as). The first thickish coat was dry to the touch in minutes but subsequent coats took a little longer. I took this to mean that the first coat was providing a good seal.
I'm planning to use it on a soon to be build router table on those bits of MDF that aren't covered in formica/laminex.

Of course this being Tasmania, I'm not likely to suffer the same issues with humidity or sunshine.