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  • Finishing MDF

    This is my first time using MDF for a project and have a couple ideas/questions to get opinions on. I am building a set of stentorians (seperate thread coming) and am at the stage where I am ready to prime and paint. I have filled holes with filler and have sanded it all down to 120g. I have read how 50/50 glue and water is a popular choice to start. Has anyone used undiluted glue before? My thoughts are its only $17/gal and it may eliminate the need for multiple coats and reduce any additional swelling that may occur with the 50/50 mix. Once that glue or 50/50 mix has dried, what grit is sufficient to sand to before priming and painting. I assume at least 220. 220 is all i have for my random orbital sander. Anything beyond that would have to be done by hand and i run the risk of leaving visible lines from where my fingers were as i sand. The wife would like them to be painted black. My thoughts would be to use rattle cans for the best finish (aside from an actual spray gun) compared to rolling. Im not looking for piano finish by any means. More or less dont want to be ashamed by them. Sent from my iPhone using Tapatalk Pro

  • #2
    The wood glue is only to seal the MDF, to make it water-resistant (not proof) and the 50/50 ratio is for cost-saving and ease of spreading. Thinning out the glue makes it easier to get a fairly smooth surface with a roller or brush. You could easily use primer (my preference, as it's cheap by the gallon).
    I typically prime (after wood putty or bondo on all the seams) and sand with 120/220 and then go a second coat sanded to 220. Then decide if a 3rd is needed again to atleast 220g.
    Then move to the color stage and do the same process but with at least 3 good coats, first coat sanded to 220, 2nd coat to 400g and any remaining coats.
    Then I spray a clear coat (of your desired sheen) to the cabinets and sand to 400g before going for a 2nd coat. I ususally go for 2-3 clear coats for durability, but it's up to you on that.
    Final coat gets sanded 220, 400, 800 and then 1500 and 2000 wet sand. I then buff and polish out and scratches.
    Not all of this is necessary - you can get a very good finish with 2 primer coats and 2 color coats and as little as 1 clear coat. I tend to sand through so I need more product to sand.
    After 4 painted cabinets - I have moved to veneer. More money for the veneer/supplies, but less labor for a nice smooth durable finish.
    Paul

    The "SB's" build page
    http://techtalk.parts-express.com/sh...-4-(pic-heavy)

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    • #3
      I'm working on gloss black MDF cabinets now. I didn't seal with the glue mix prior to priming, instead went with a rattle can filling primer. Thick coat, sanded to 320, 2nd thick coat and sanded to 400. Then the gloss black went on, 2 coats. Then I wet sanded with 600, which went through to the primer in spots, leading to another 2 coats of black.

      That's where they sit now, with 1000g ready to wet sand, followed by turtle wax rubbing compound, followed by auto polish. I'm not going for piano finish either, just really uniform.

      Get a 3M rubber sanding block to keep it level without using your orbital.
      Electronics engineer, woofer enthusiast, and musician.
      Wogg Music

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      • #4
        I'm no expert here ... but there was a thread in the last few months were primer flaked off the MDF surface (not edge). IIRC correctly, there may be some "oily or waxy" residue on the surface left over from mfg and the solution was to wipe down the panels with alcohol, again IIRC.

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        • #5
          Originally posted by Millstonemike View Post
          I'm no expert here ... but there was a thread in the last few months were primer flaked off the MDF surface (not edge). IIRC correctly, there may be some "oily or waxy" residue on the surface left over from mfg and the solution was to wipe down the panels with alcohol, again IIRC.
          Good point... I'll add that I sanded the bare MDF with 120 prior to doing any painting. That was mostly to flatten butt joints to level, but had the side effect of prepping the MDF for primer.
          Electronics engineer, woofer enthusiast, and musician.
          Wogg Music

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          • #6
            Zinsser BIN shellac based primer, especially on the mdf end "grain", the cut surfaces that expose the interior of the mdf.

            Rattle cans on a big box like the Stentorians will give you a very sore index finger. You could roll on latex paint, do a vinyl wrap if you just gotta have gloss.

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            • #7
              Zinsser BIN is excellent stuff, really it is just tinted shallac - so prime and seal in 1 step and sands very nicely.

              As for rattle cans, Rustoleum makes a gun attachment to save you from the finger cramps.
              Click image for larger version

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              Don't waste your money on a new set of speakers, you get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

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              • #8
                Wolf I believe uses undiluted glue. Maybe he will chime in.

                I use 50/50, just out of habit I suppose more than anything else. It worked for me the first time, so I continue to use it. Had I used undiluted glue, I'd likely still be doing that.

                I don't prime, I like all color coats. If I were a better painter, maybe I'd use primer. But nothing is worse than being almost done and sanding through to your primer.

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                • #9
                  Trigger-caps really he!p! No sore fingers! I use Elmer's white glue straight, no water. Don't sand heavy handed, or the resin will melt and flake if it went on too thick. Use a roller or brush to apply the glue thinly and evenly.
                  Later,
                  Wolf
                  "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                  "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                  "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                  "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                  *InDIYana event website*

                  Photobucket pages:
                  http://photobucket.com/Wolf-Speakers_and_more

                  My blog/writeups/thoughts here at PE:
                  http://techtalk.parts-express.com/blog.php?u=4102

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                  • #10
                    Originally posted by djg View Post
                    Zinsser BIN shellac based primer, especially on the mdf end "grain", the cut surfaces that expose the interior of the mdf.

                    Rattle cans on a big box like the Stentorians will give you a very sore index finger. You could roll on latex paint, do a vinyl wrap if you just gotta have gloss.
                    +1 Rattle cans will be an expensive disappointment. Foam roller and oil based if you can leave it alone for 2-3 weeks. Benjamin Moore Advance if you can leave it alone for a week. Foam roller and black latex can look good if it's flat sheen.
                    John H

                    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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                    • #11
                      Mitered corner joints and vinyl wrap, duratex on the baffle, easiest finish job ever. Something to consider for future projects.
                      Click image for larger version

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                      My modest builds:
                      Armadillo TM, A.K.A. Lil' Dillo
                      Tarkus/Armadillo build #2
                      Armadillo Center Channel
                      Au-Rock-O Sub
                      Tarkus
                      Staining MDF tutorial

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                      • #12
                        Wow thanks for the responses guys! Alot of great info! I guess one other thing i failed to mention that this is a budget finish process. Single income family with two babies and a new house payment shrinks any disposable income. For an update, i have just applied a skim coat of undiluted glue on the bottom of one of the enclosures. Ill let that dry and see how that done. Sent from my iPhone using Tapatalk Pro

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                        • #13
                          Given the budget and size of those cabinets, I'd go foam roller and latex, sanding and re-coating until it meets your expectation.

                          My rattle can primer and gloss work is a lot of sweat on my tiny, tiny cabinets and would be a whole lot of time and sweat on those monsters. Also, without experience you're likely to keep having to re-do stuff like I am.
                          Electronics engineer, woofer enthusiast, and musician.
                          Wogg Music

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                          • #14
                            My thoughts exactly. Should i sand the color coats? Sent from my iPhone using Tapatalk Pro

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                            • #15
                              Originally posted by ameuba10 View Post
                              My thoughts exactly. Should i sand the color coats? Sent from my iPhone using Tapatalk Pro
                              Yup, with some really fine grit, maybe 320 or 400. Then adjust when you mess it up like I've done repeatedly ;) Sent from my SM-G920P using Tapatalk
                              Electronics engineer, woofer enthusiast, and musician.
                              Wogg Music

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