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Thread: Finishing MDF with Polyurethane

  1. #1

    Finishing MDF with Polyurethane

    I posed the question of "what is polyurethane coated MDF" in General Woodworking, but it failed to generate.

    A search on the internet for garage cabinets turns up quite a few hits for "polyurethane coated MDF".

    Has any done this? Can you provide any details on what you did, and the results?

    The MDF cabinets will be face-framed with solid wood (poplar).

    I have HVLP. For some reason, I'm resisting the option to paint, maybe because it's too common.

    Thanks,

    Mike

  2. #2
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    One of my favorite utilitarian desk top material is MDF with a urethane finish. I like the look - a nice even color, kind of like cork without the texture, that looks great with maple or mahogany or walnut etc. etc. I'm sure it would be a great looking door panel (though with a different wood surround than clear poplar ). I have used this treatment for desks in a design studio, reception desk for a hotel, on a small lightly used floor, and on a number of computer desks in various offices. The desks were usually trimmed with a solid wood edge to match the cabinetry. To the specifics of your question - a spray urethane on MDF makes good sense to me.
    Sam

    ~ Hard to take a guy who looks like this seriously but his 2 is worth all of that ~

  3. #3
    If it were me, I'd spray the MDF with a seal coat of shellac first. Then I'd top with poly. I think poly is a fine finish for garage cabinets.

    The issue I believe is MDF's structural integrity. Garage cabinets normally need to be strong. MDF sags pretty easily under any kind of prolonged load.

  4. #4
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    >>>> "polyurethane coated MDF".

    I strongly suspect that the above is referring to two part polyurethane, not the consumer type poly varnish you would buy in a big box. The two part poly is not a finish that the amateur finisher can use.

    If you knew the above and were asking about the use of pre-finished panels, then they are something you can use. Many cabinet shops have been using pre-finished sheet stock for a number of years. For kitchen cabinetry it is quite a time saver. It provides a nice interior for cabinets in its one sided type and makes for a durable exterior in either its one sided or two sided type.
    Howie.........

  5. #5
    Quote Originally Posted by Howard Acheson View Post
    >>>> "polyurethane coated MDF".

    I strongly suspect that the above is referring to two part polyurethane, not the consumer type poly varnish you would buy in a big box. The two part poly is not a finish that the amateur finisher can use.

    If you knew the above and were asking about the use of pre-finished panels, then they are something you can use. Many cabinet shops have been using pre-finished sheet stock for a number of years. For kitchen cabinetry it is quite a time saver. It provides a nice interior for cabinets in its one sided type and makes for a durable exterior in either its one sided or two sided type.
    Howie,

    As you could guess, the websites are not that specific as to what type of polyurethane.

    What is a "pre-finished panel"?

    The MDF I'll be using is cabinet grade, not from the box stores. I'm impressed with quality of the surface of this MDF, to paint it would be a waste.

    The MDF cabinets I've made in the past (never finished), have held up extremely well, possibly due to the use of solid wood face frames. I know alot of people bash MDF for it's lack of durability, but my gosh, I'm not in an industrial enviroment!

  6. #6
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    I guess I didn't read very well between your lines . I am a huge proponent of prefinished sheet goods. Nearly always use prefin maple for cabinetry interiors as well as for the exteriors of some frameless "economy" projects. Haven't used prefin MDF though. My comments above were for shop finished MDF using ML Campbell clear finishes as well as some brushed on urethane. Just know that not all prefin is created equal, but if you are purchasing cabinet grade from a reputable plywood dealer to the trades you should be fine.
    Sam

    ~ Hard to take a guy who looks like this seriously but his 2 is worth all of that ~

  7. #7
    I've done this on several occasions.

    I take regular box store brush on poly and mix it 50/50 with mineral spirits and then just wipe it on. It supper easy to apply, and dries fast (I've applied 8 coats in a day before). Every 3 or 4 coats I wet sand with 300 or 400 hundred grit. After it's cured for a few days, I finish it off with paste wax.

    The top of this dust collector was finished with this method..
    http://www.dans-hobbies.com/2008/07/...ust-collector/
    -Dan

  8. #8
    Quote Originally Posted by dan sherman View Post
    I've done this on several occasions.

    I take regular box store brush on poly and mix it 50/50 with mineral spirits and then just wipe it on. It supper easy to apply, and dries fast (I've applied 8 coats in a day before). Every 3 or 4 coats I wet sand with 300 or 400 hundred grit. After it's cured for a few days, I finish it off with paste wax.

    The top of this dust collector was finished with this method..
    http://www.dans-hobbies.com/2008/07/...ust-collector/
    I like it! Now I know how my project will look.

    Did you use any type of sealer?

    Thanks!

  9. #9
    Quote Originally Posted by Mike Shields View Post
    I like it! Now I know how my project will look.

    Did you use any type of sealer?

    Thanks!

    No sealer, just the poly. The first few coats will get sucked up like a sponge, so you can really slop them on. Depending on the grade of MDF you are using, after say 8 coats or so you will have to make sure to wipe off any excess.
    -Dan

  10. #10
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    Just did this exercise. I made some new shop cabinets that go under the assembly table. I had some outdoor clear coat, basically poly, and put on 4 coats with a foam roller. As Dan said, the 1st two coats suck it up and feel bumpy, the next 2 smooth it out. I sanded between the coats. I want to put on a few more.
    Don

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