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Thread: MDF smooth and rough sides?

  1. #1
    Join Date
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    Cool MDF smooth and rough sides?

    Hi friends. I am working on a project and have used some 1 inch MDF for some parts of it. One side of this material is really smooth, but the opposite side is fairly smooth, but when sanded seems to "feather" and the surface will not come real smooth.

    Did I make a mistake in using this stuff? Does all MDF have an A side and a C side (comparing to plywood grading)?

    It is all going to be painted, so it will be primed. Can i get away with sanding, priming and sanding (rinse and repeat as needed) to get this surface to come out smooth?

    Am I doomed to one side that might look a little rough.

    Help? My wife is waiting for this project to be finished.

    Aloha, Tony
    "You got to learn from the mistakes of others. You won't live long enough to make them all yourself". (Author unknown)

    "Time flies like..... an arrow,,,Fruit flies like..... a banana." Groucho Marx

    Ah,,,to live in Paradise!

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    Fighting for all I am worth, and praying every day.

  2. #2
    Join Date
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    All of it around me seems to be pretty much the same on both sides. I'd never suggest sanding MDF, but if you prime it with a good sandable primer you can get it smooth (the primer). It's fairly common to seal the edges with such a primer, or glue size, or whatever, and then sand them to get them smooth as the field surface. I've had good results with shellac based BIN, so I haven't tried anything else.

  3. #3
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    I normally seal MDF with SealCoat before doing any sanding. Double or triple coat the edges.
    Bill Arnold
    Citizen of Texas residing in Georgia.
    NRA Life Member and Member of Mensa
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  4. #4
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    Yep, even a light spray of shellac will allow you to sand MDF to a high sheen.

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  5. #5
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    and i will third the above mentioned ideas of sealing first.
    If in Doubt, Build it Stout!
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  6. #6
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    Thanks Guys. I have now primed it all with a sandable primer and will try some sanding with the 220 again when it dries enough.

    I could not really see why one side would be smooth and stay smooth when sanded, and the other side was not as smooth to begin with, but got rougher after a light sanding.

    I was using 220 grit on my ROS, lightly, but I guess I should not have done that. I originally planned to spray a lacquer sealer I have, and finish the project in lacquer, but that changed.

    I will let you know how things turn out when I do the sanding.

    Aloha, Tony
    "You got to learn from the mistakes of others. You won't live long enough to make them all yourself". (Author unknown)

    "Time flies like..... an arrow,,,Fruit flies like..... a banana." Groucho Marx

    Ah,,,to live in Paradise!

    Registered voting member

    Fighting for all I am worth, and praying every day.

  7. #7
    Join Date
    May 2011
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    MDF can be a frustrating son of a gun to work with at times. And this is one of them.... As others have stated above prime sand prime sand will go a long way to getting a smooth fuzz free surface. Shellac based primers help and there are other products out there specifically for mdf. A friend of mine used to use a 50/50 solution of yellow glue and water and brush it on then lightly sand it smooth. (never tried it myself as I avoid the product as much as possible. reeks havoc with my respiratory system)

    You may see better results if after the second coat of primer you sand with 400-600 grit with a pad sander and just light passes to knock any residual fuzzing. A RO may be too aggressive.

    Where this will really matter is if you are spraying vs rolling/brushing.
    He who laughs last, thinks slowest

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