MDF Lacquer Coating

[JR]

I am trying to coat MDF with a white lacquer. The piece has routed beveled edges. The edges have been sanded to a 220 grit before coating.

I applied a clear sealer to the piece and 3 coats of gloss white. The flat surface is fine but the routed edges are sucking up the lacquer and showing something like raised grain and all the router marks. This continues to happen regardless of how well the preparation is done.

Anyone have any ideas as to what's wrong? Am I trying to do the impossible?

TIA,

-JR

[Andy Dingley]

MDF always does this.

Use a proper MDF primer, and certainly avoid other water-based primers. They'll raise fibres on the surface.

To seal the edges, apply the primer and then sand. Repeat until happy.

If you want a non-priming MDF, try Valchromat. This contains extra melamine and also a pigment, so you get it ready-coloured and a usable surface, straight off the router.

[Not Telling]

I agree with Andy, water based stains and primers as such will cause the problems. Sealing with the right type of primer is the trick. As long it is one designed for MDF. I do not understand why you are having router marks unless the bit is dull or to much pressure being appllied during routing. I router MDF for custom made show cases from time to time and have only experieced router marks one time caused by a dull bit. Learned that MDF dulls bits easily go to use carbide.

[Tom Watson]

When I do this sort of thing I sand to 320 and apply two coats of a white, high solids, solvent based sanding sealer to the machined edges. Then I sand these areas 180-220.

After prepping the worked areas in this way I finish the whole piece according to the regular finishing schedule.

Regards, Tom. Thomas J. Watson-Cabinetmaker Gulph Mills, Pennsylvania