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