Finishing raw MDF edges.....question?

Discussion in 'Home Theater Projects' started by Mike Allen, Nov 9, 2003.

  1. Mike Allen

    Mike Allen Stunt Coordinator

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    Hey guys,
    I'm about to start building a few pieces of A/V furniture including a box for a Tempest(can't wait[​IMG]).

    My plan is to paint the MDF with a black semi-gloss, and finish it with 2-3 coats of satin polycrylic.

    I've been playing around with some test pieces. I've achieved a very nice rounded off edge that I'm happy with. Now comes the finishing.....

    I sanded the raw edges first with 200 grit, then down to 400 grit. I've got a very smooth surface that I thought would take paint well, but apparently not. I'm having a hard time getting the same finish on the edges as I am on the surface of the MDF. While it's very smooth, it still soaks up more paint, and has an obviously different finish when dry.

    What can I do to get a uniform finish on the surface AND the edges of the MDF? Is there a certain type of filler/primer/etc that will help me get a silky smooth surface? I thought about wet sanding the edges down to 1000 grit, but I have a bad feeling about putting anything wet on the raw core of the MDF. I'm pretty sure it will warp and peel apart like cardboard if I do that.

    I appreciate any comments. Thanks [​IMG]
     
  2. Allen Ross

    Allen Ross Supporting Actor

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    Mr. Allen, Ordinary primer, two coats worth, then paint and you will be golden
     
  3. Mike Allen

    Mike Allen Stunt Coordinator

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    Allen,
    Thank you for the reply.

    I'm new at this, so I'm sorry for these very stupid questions......

    1.) Is the primer made up differently than paint? Will the edge not soak up the primer like it does the paint?

    2.) Should I use a oil or water based primer? Same question applies to the paint? It will have a couple of coats of polycrylic over the paint.

    3.) Should I prime the whole thing(surface and edges)? Or just the edges? If I only prime the edges, won't I get a little different finish than I would have on the surface?

    3.) And should I lightly sand after I prime so I can get a very smooth finish? Or is it not a good idea to sand after the primer?

    Thanks [​IMG]
     
  4. Bob Kavanaugh

    Bob Kavanaugh Second Unit

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    Use Durhams Rock Hard Water Putty. It comes in a powder, mix it up with the appropriate amount of water, smear it on the raw edges, THEN sand smooth. You will be happy. The only hardware store I know of that has it is ACE.

    Good luck with that.
     
  5. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    Sanding sealer also works well, a couple coats hand painted/rolled on then do your sanding. Primer is thicker than paint. Sanding sealer is thicker than primer even. Both are just intermidiaries between the surface and the paint, preventing the material from absorbing the paint. The material absorbs a small amount of the primer or sanding sealer (i've found MDF edges can soak up ALOT of primer, that's why I suggest sanding sealer) while the surface is uniform, allowing the paint surface to be uniform also. Oil/water based is not that big of a deal since it's going to be used indoors. Whatever you have, can get, or prefer.

    1.) Apply Sanding Sealer
    2.) Sand
    3.) Paint

    Hope this helps [​IMG]
     
  6. Ryan Hawke

    Ryan Hawke Agent

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    I made some picture frames from some leftover speaker MDF and wanted to finish the edges, so I used primer. A fairly heavy coat of primer (Ace Hardware brand) and a lot of sanding gave great results.
     
  7. Allen Ross

    Allen Ross Supporting Actor

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    i have always done at least two coats of primer and sanded with higher girt each time, i ended around 300 grit. then painted.
     
  8. Mike Allen

    Mike Allen Stunt Coordinator

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    Thanks for the replies everyone [​IMG]

    I did a little reading around, and from the info I gathered from this thread and elsewhere, it sounds like the sanding sealer is probably best for me. I'll give it a try this weekend and see how it turns out.

    And Allen Ross.....Last night, I spent a while looking through all your pictures on your website. Very nice photography work man....your pictures are great. Do you work in the photo industry? I take it you like a beer now and then [​IMG] And if I may ask, what happened to the speaker on this page? Did it fall of your shelf or something? Bummer.

    Thanks guys!
     
  9. Pete Mazz

    Pete Mazz Supporting Actor

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    Whatever you do, let the edges dry before applying more. If you just keep laying on sealers and such, thinking that more must be better if it's still soaking in, think again. All you'll wind up doing is swelling the edge. Apply a normal coat, let dry and re-apply.

    I use thinned wood putty or paste wood filler smeared on an edge. It sands much smoother and seals very well without multiple coats of sealer.

    Pete
     

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