High-gloss finish on MDF
M.L. campbell has a brochure covering finishing MDF.
Sand all surfaces with 320-400 No-fil paper, and all routed edges with 600. Apply two coats of catalized primer such as Clawlock, sanding between coats with 320 No-fil. Apply a wet coat of Resistant or Magnalac, followed by a coat of Krystal or Clearlite Plus Gloss (I have only tried Clearlite Plus over Magnalac).
Allow to dry for at least 24 hours, then sand with 1500 paper to remove any imperfections such as dust and orange peel, and follow that with 2000 (8 microns) paper.
Polish with a high speed-polisher and an automotive rubbing compound, followed by a swirl remover.
There are three good systems out there for MDF: the conversion varnish, polyurethane, and polyester systems.
The system that is best for you depends on your spray equipment, skill level and production line. I prefer polyester primers because they are very high solids, produce no shrinkage, and there's no worry about mil thicknesses. Once cured it is not going to move anywhere! Also, you can topcoat polyester with anything you want; urethanes or varnishes. Urethanes will give you a higher gloss off the gun than varnish, but once again varnish will limit the build to 4 dry mil. If you plan to polish I like a little more there for safety reasons... like that rare slip of the buffer!!
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