Painting Freshly Cut MDF

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Old 01-04-17, 07:50 AM
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Painting Freshly Cut MDF

I'm making a subwoofer enclosure out of MDF with recessed baffle, and will be cutting a 1/2" roundover in the front baffle. I did this on a previous build and the area I cut was dull whereas the surrounding undisturbed surface was nice and shiny after the first coat. What's the best way to ensure the paint on the routed area looks the same as the un-routed areas? I am using a spray can of paint and primer in-one. I realize it's because the wood is soaking up the paint, so I'm trying to determine how best to prevent this.
 
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Old 01-04-17, 08:30 AM
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Try a glue size. Mix pva wood glue and water 50-50 and paint it on the cut area. Let it dry and then sand lightly with 220 grit sandpaper.

Another approach often used on MDF is to butter the cut edge with a thin coat of sheetrock joint compound, let it set, and then sand. This approach is better if you have any tearout in the cut areas, which is pretty common on MDF.
 
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Old 01-04-17, 08:32 AM
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Paint and primer in one is not primer. I would use an actual primer first.
 
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Old 01-04-17, 08:40 AM
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Another approach often used on MDF is to butter the cut edge with a thin coat of sheetrock joint compound, let it set, and then sand.
That's the method I use. You'll get better coverage and a heavier film of paint if you brush or roll the paint. The paint in aerosol cans is drastically thinned!
 
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Old 01-04-17, 08:49 AM
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I sand the cut edges then prime everything with a sandable primer. After the primer has dried, I sand it all lightly before painting.
 
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Old 01-10-17, 07:47 AM
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I ended up using DAP vinyl spackling on all the edges and routed cuts and sanded everything smooth. Now I need tips on the painting process, primarily how many coats and when to wet sand. For example, do I wet sand after each coat, or after every couple coats? Do I sand after priming, painting, AND clear coat? Is 400 grit a good grit to use or should I go with 600? Use a soapy solution?
 
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Old 01-10-17, 07:50 AM
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I can't imagine wet sanding MDF. I wouldn't use a clear coat on it either.
 
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Old 01-10-17, 07:55 AM
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Finishing wood or MDF isn't the same as finishing metal. You should always sand and remove any dust between coats.
 
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Old 01-10-17, 08:45 AM
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Mark,
Did you mean to say prepping wood or MDF is different than metal? Because once the primer coat is on the color coats & clear coat (if desired) is exactly the same as painting metal.
 
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Old 01-10-17, 09:01 AM
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Painting metal usually requires thinner coats of paint and finer sanding than painting wood/mdf. With wood/mdf you want a heavier coating of paint to make the finish appear smoother, with metal you already have a slick surface. No need to wet sand when the heavier coating will fill in the minute sanding scratches.
 
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Old 01-10-17, 09:22 AM
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I get way better results when I prime first.

After that it doesn't matter what the substrate is.

In fact you CAN polish a turd...if you prime it first
 
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Old 01-10-17, 11:20 AM
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Just to be clear I wasn't suggesting to not use a primer. A raw substrate always needs a primer [including patches on previously painted surfaces] Repaints don't always need a primer. The big difference between painting metal versus wood or drywall is the mil thickness of the coating applied.
 
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