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Painting MDF (1 Viewer)

Ron D Core

Stunt Coordinator
Joined
Mar 31, 2002
Messages
158
I will be painting a baffle a satin black color. The speakers are flush mounted and the recesses have been rounded over with a 1/4" bit. The edges have a 45 degree chamber. Any suggestions on how to get a nice, smooth finish on that? All I could think of is lots of sanding, primer and coats of black then more sanding. Is there a certain type of paint or primer that works well with the fibrous texture of MDF?
 

Jeff Rosz

Second Unit
Joined
Sep 24, 2000
Messages
335
as for the the round-overs and bevels, they will suck up alot of paint. fill them with filler. for the round-overs, get one of those 3M "sponge type" sanding pads. they will have 2 grits...fine on one side, finer on the other. use only the finest grit side. sand the filler nice and smooth. then fill and sand again. then get even finer grit paper and use it with a soft kitchen sponge for the final sanding. use only the lightest of pressure because you dont want to deform your round-overs.

mdf comes in what i call the soft or hard types. the hard type has a paper-like look to the face. the soft kind has a pulpy look. know what i mean? if you have the soft kind, seal it, or it will leave "pin holes". then prime, let dry, wet sand(400 or better), mist water & wipe, let dry, repeat. between sandings, CLEAN THE PAPER! dont let "pads of powdered paint" build up on the paper. i use paper towels for wiping the surface clean and a spray bottle of water for a fine mist. then finish with the satin. satin is easy, gloss is tough. especially where i live, the humidity is a killer. wish i could paint in arizona, heh.

i use the more expensive krylon paints. whatever brand you buy, use the same brand primer.
 

Dave Milne

Supporting Actor
Joined
Jul 2, 2001
Messages
568
If you want a smooth surface on MDF, especially edges, then get some high-solids lacquer primer-surfacer from an auto paint supply store. It fills in the voids, dries quickly, and sands easily, without clogging. To get the smoothest surface, make sure you let it fully shrink for a few days before sanding.

The above assumes you have access to spray equipment. I've never tried brushing this stuff but it dries very quickly. It would be difficult to cover a large surface with a brush without having it film over and drag.
 

Bryan Michael

Supporting Actor
Joined
Mar 2, 2002
Messages
564
i have 3 coats of flat blac on my ends and i am going to put on at least 2 more but i have to sand a bit
 

Chris Carswell

Supporting Actor
Joined
Mar 5, 2002
Messages
598
Kilz works good. Use in a WELL ventlated area. Smells like hell. Dave and Jeff both had good ideas. I have used automotive stuff before as well as put in filler. I like that one the best but it takes forever and becareful not to sand too deep :)
 

Dan Wesnor

Second Unit
Joined
Apr 28, 1999
Messages
389
Use wet-sandable primer (it will say so on the can). Spray it on, let it dry an hour. Then put a few drops of water (per sq. foot) on it and go at it with 320 or higher grit sandpaper. I used a 1/4 sheet sander. The primer will form a paste which will dry smooth.

Be sure to have plenty of Lava soap handy.
 

John E Janowitz

Second Unit
Joined
Oct 30, 2000
Messages
445
Another option that works well for sealing the roundovers and ends of the mdf is to mix up some fiberglass resin and paint it on. It will soak in and seal up the edges. Then just sand, quick coat of primer, and paint.

John
 

Dave Milne

Supporting Actor
Joined
Jul 2, 2001
Messages
568
Dan,
My experiences wet sanding primers on MDF are bad. Primers have sufficient porosity (as well as possibly microscopic pinholes and cracks) that allow water to come in contact with the MDF. Water and MDF just don't mix. It swells like crazy and you end up with a mess. For final-sanding topcoats, you can usually get away with wet sanding acrylics, alkyds, or polyurethanes, but lacquers are still risky.

Sufficiently hardened lacquer primer-surfacers dry sand beautifully --into a fluffy powder that never clogs. There's no reason to wet sand.

Ron,
You can pick up good primer-surfacer at the auto-paint store on the corner of Grant and Stone. The Western brand is inexpensive. Or I usually have a gallon or two lying around and I'd be glad to give you what you need. I also have lacquer thinner in large drums; you'll need some for cleanup.
 

Ron D Core

Stunt Coordinator
Joined
Mar 31, 2002
Messages
158
Sounds good, I'm thinking I'll need to get my hands on a good spray gun and tank for this part. Dave, I might just take you up on your offer. But I don't plan on doing this for about 6 weeks anyway. When I do get down to it, I want to do it right the first time so I may need some help. I'm just researching and brain-storming in the meantime.
 

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