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Bondo/elmers/gluewater on MDF...

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  • mmu7
    replied
    I made the mistake of using an orbital sander and that basically destroyed the edges by unevenly removing too much. Would a finishing sander fair better?

    Leave a comment:


  • lunchmoney
    replied
    Re: Bondo/elmers/gluewater on MDF...

    Originally posted by mtmpenn View Post
    Any advice for me?

    I filled, then put on a coat of Zinser Shellac based primer.

    Then, I noticed that some places need to be filled again. Problem is the joint compound I was using to fill does not seem to stick to the shellac.

    Any advice?

    Thanks,
    Mike
    You might try 3M Acryl Green Putty... specifically intended for fixing imperfections after you've primered.

    I know it works perfectly after using typical paint primers... although I'm not familiar with a shellac-based primer.

    Leave a comment:


  • jerryanderson
    replied
    Re: Bondo/elmers/gluewater on MDF...

    Probably should go back to the ol reliables! Diluted wood glue's, clear poly's or minwax seal & sand. They allways work!!

    Leave a comment:


  • mtmpenn
    replied
    Re: Bondo/elmers/gluewater on MDF...

    Any advice for me?

    I filled, then put on a coat of Zinser Shellac based primer.

    Then, I noticed that some places need to be filled again. Problem is the joint compound I was using to fill does not seem to stick to the shellac.

    Any advice?

    Thanks,
    Mike

    Leave a comment:


  • lunchmoney
    replied
    Re: Bondo/elmers/gluewater on MDF...

    Originally posted by jonpike View Post
    I'll second the Shellac... I think any water you get into the MDF will take a while getting back out. The Alcohol that is Shellac's base evaporates much faster, and doesn't seem to cause as much swelling while it's in there.
    So everyone keeps saying...

    But in my experience that's simply not the case... on my three Tritrix speakers, I did two with wood glue/water and one with shellac...

    The slight emergence of seams has been equivalent on all 3 speakers... the shellaced speaker did not perform any better than the wood glued speakers.

    I did, however, find that the wood glued speakers sanded much better... the shellac tended to gum up upon sanding, particularly on the roundovers.

    So I'll stick with the wood glue/water

    Leave a comment:


  • lunchmoney
    replied
    Re: Bondo/elmers/gluewater on MDF...

    I use about 60/40 Titebond II and water, about 4 coats over the entire cabinets... works great...

    See my SR71 build thread here for more details...

    http://techtalk.parts-express.com/sh...d.php?t=208196

    By the way it's been about 5 months now, and the seams still look very good... you can see the seams have emerged ever so slightly in a few places, but it's unnoticeable unless you really look for it... I doubt you could ever hide the seams 100% forever, regardless of the technique... no surface finish could ever completely prevent the mdf from expanding/contracting

    Leave a comment:


  • tpremo55
    replied
    Re: Bondo/elmers/gluewater on MDF...

    I use this: Deft Sanding Sealer

    It will require multiple coats on end grain MDF, but is cost effective and seems to work well. That said, I've only veneered cabinets that I've used Delf on. Would probably take quite a few coats on end grain, I think I used 4 when I was veneering, and would double that for paint.

    I've also used diluted TightbondII, and TBII with MDF sawdust as a filler (50/50). I buy TBII by the gallon and always seem to have plenty of MDF sawdust laying around. :D

    Used to use Bondo - may again.

    Leave a comment:


  • williamrschneider
    replied
    Re: Bondo/elmers/gluewater on MDF...

    If shellac is used, be sure it's de-waxed shellac like the Zinsser Seal Coat mentioned above.

    Many shellacs contain wax which will interfere with adhesion of top coats.

    Leave a comment:


  • jonpike
    replied
    Re: Bondo/elmers/gluewater on MDF...

    I'll second the Shellac... I think any water you get into the MDF will take a while getting back out. The Alcohol that is Shellac's base evaporates much faster, and doesn't seem to cause as much swelling while it's in there.

    Get a quart (or gallon!) of Zinnser's Seal Coat... and some more denatured Alcohol. Mix the Seal Coat and Alcohol 50/50 in a jar, for a thin, penetrating mix.

    Brush it on till it stops soaking in. Inside and out. Special attention to the edges. You'll be amazed how much will get drunk up.

    Wait a few hours to overnight, do it again. Maybe a third time, or 4th. Maybe use full strength for the third coat or 4th... when it slows down absorbing more you know you've done enough. Let it dry at least a day or two.

    You now should have a well stiffened and sealed layer in the MDF surface. Sand and enjoy how hard it is and how well it sands to flat smooth edges. Coat with glue and veneer, or start laying down some primer and paint layers...

    Sealing inside and out will help the box to not soak up moisture/lose moisture as the seasons go by, and not have the joints move and show thru the finish.

    Might be an idea to build the box, and put it somewhere warm and dry for a week or so... before starting the sealing and finishing. There was a guy on here (Aaronpro?) who did amazing sculpted boxes with auto paint finishes.. he finally resorted to a DIY heater box with a couple of 500W light bulbs and a fan as a hot air source, to bake out his boxes for a few days to insure MDF stability...

    Stabilizing and sealing well should go a long way to keeping the MDF from moving.

    Leave a comment:


  • JRT
    replied
    Re: Bondo/elmers/gluewater on MDF...

    Sherwin Williams "Icing" p/n US2606 pourable brushable polyester autobody filler putty is good for edge sealing and light filling.

    Leave a comment:


  • nikbrewer
    replied
    Re: Bondo/elmers/gluewater on MDF...

    I got one word for you

    Veneer. I find it so much asier thn paint. ALso, if i plan on painting something, i veneer it with scraps now just to seal the grain

    Leave a comment:


  • arlis_1957@yahoo.com
    replied
    Re: Bondo/elmers/gluewater on MDF...

    the sandable primer drys very fast. remember, glossy paint will always show off the smallest of flaws. i used a primer-sealer and then spray paint and then i used water based spray for the final finish its really great.


    ps did you forget to recess your tweeter?

    your baffle looks real nice. you can handle your router real well.



    http://s413.photobucket.com/albums/p...ster%20sealed/

    Leave a comment:


  • davepellegrene
    replied
    Re: Bondo/elmers/gluewater on MDF...

    my joints didn't show up until after the paint as well. primer didn't show them and you could not feel them. most people won't see them unless you tell them to look for them though.
    You may have rushed the process. Your fillers may not have been completely dry. As they dry they will shrink. Same goes for primer. Especially if you lay it on thick. The cracks are the deepest fill so they may have shrunk the most.
    Dave

    Leave a comment:


  • djarchow
    replied
    Re: Bondo/elmers/gluewater on MDF...

    Here is a thread over on DIY Audio addressing this very subject.

    http://www.diyaudio.com/forums/showt...652&highlight=

    Regards,

    Dennis

    Leave a comment:


  • jerryanderson
    replied
    Re: Bondo/elmers/gluewater on MDF...

    Originally posted by MidKnight View Post
    FBOV:

    I didn't do a thing different on the baffles. I think the difference came in the fact that I'm using a textured paint on the baffle plus there's a roundover into the endgrain instead of a **** joint. The "texture" added by the painting of the endgrain just matched the textured paint.

    EVERYONE:

    Thanks for all the responses. Amazing.

    I seems that the painting process is the longest of all the steps in the build process. In my spare moments in the evening it would take me a few weeks to seal/prime/paint/coat. I have to do one at a time due to space constraints on my small apartment balcony. Not to mention my "paint box" doesn't look too good out there.

    Again, thanks for all the info! The next round will be better. And the good news is that I can always make new cabs and take my sweet time and just transfer the drivers, crossovers and binding posts to new cabs later.

    Judging by the pic's, your baffles do look nice...great work! Good things come to those who have patience!

    Leave a comment:

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