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  1. #1

    Default MDF Sealant Horror

    On the recommendation I found, I bought a can of Zinser Shellac Universal Wood Sealant for use on MDF prior to painting.

    Well, I applied the stuff, and to my shock and horror, as it started drying (which it does rapidly), it started developing crinkles or stress lines; the way the top-most layer of ice looks as it just starts to freeze. I let it dry over night, and then sanded. The sanding reduced some of the crinkles, but they're still there. I'd had to sand right down to bare MDF to get rid of these defects.

    Why did this happen?


    Did I not stir enought? How much stirring does it need? A couple of hours? A couple of days? This crap may've ruined my project.

  2. #2
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    Default Re: MDF Sealant Horror

    I know what you are talking about. I used there latex based primer and had similar effects?!?

    I recommend slathering the cabinet in undiluted elmer's wood glue. This will seal it very well.

    Thisis the product that didn't work for my mdf unless I used multi-coats....


    http://www.zinsser.com/product_detail.asp?ProductID=11

  3. #3
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    Default Re: MDF Sealant Horror

    Sorry for the disaster! Can you post a pic of what it looks like after sanding?

  4. #4

    Default Re: MDF Sealant Horror

    Quote Originally Posted by supermike View Post
    On the recommendation I found, I bought a can of Zinser Shellac Universal Wood Sealant for use on MDF prior to painting.

    Well, I applied the stuff, and to my shock and horror, as it started drying (which it does rapidly), it started developing crinkles or stress lines; the way the top-most layer of ice looks as it just starts to freeze. I let it dry over night, and then sanded. The sanding reduced some of the crinkles, but they're still there. I'd had to sand right down to bare MDF to get rid of these defects.

    Why did this happen?


    Did I not stir enough? How much stirring does it need? A couple of hours? A couple of days? This crap may've ruined my project.
    You may be able to remove it with a lot of solvent. Typically shellac thinner. Or let it dry thoroughly for several days and then sand and sand.

    The problem is that the MDF absorbed the solvents from the shellac/sealer very quickly. Thinning the shellac and then a light application is what would probably work best. Apply with whatever and then wipe off excess with a rag.

    I had an almost similar thing happen with one of my MDF projects.
    Project wasn't ruined, but it took lots of sanding to get it right.

  5. #5
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    Nov 2006
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    Iowa
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    Default Re: MDF Sealant Horror

    Quote Originally Posted by View Post

    The problem is that the MDF absorbed the solvents from the shellac/sealer very quickly. Thinning the shellac and then a light application is what would probably work best. Apply with whatever and then wipe off excess with a rag.
    I agree with AE, I have never had the bullseye dewaxed shellac craze or orange peel unless I applied it too thick, or if there was an underlying finish such as oil that was not 100% dry yet. Denatured alcohol is the solvent for shellac if you want to try to remove it.

    Good luck,

    Dennis

  6. #6
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    May 2007
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    Athens, Ohio USA
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    Default Re: MDF Sealant Horror

    Quote Originally Posted by supermike View Post
    On the recommendation I found, I bought a can of Zinser Shellac Universal Wood Sealant for use on MDF prior to painting.
    I've never used that, but the way it crazed makes me think it's very different from my usual Zinsser sealer...




    I slather the sanding sealer on MDF, let it drink into the end grain, etc. and have never had crazing.

    I've used the Bulls Eye primer shown above before, but it didn't sand very well (understatement!). Each product in the Zinsser lineup is different for a reason I guess.
    Bill Schneider
    -+-+-+-+-
    One word = one milli-picture

  7. #7
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    Sep 2005
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    Irvine, CA
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    Default Re: MDF Sealant Horror

    Weird... It doesn't need any stirring. Is what you used the same in Bill's picture? Wondering if you've got some other Shellac based sealer.

    I'm usually "Mr Use Seal Coat, it's Cool" around here, it's always a fairly thin shellac and soaks in pretty well. I usually cut it 50:50 with denatured alcohol for a thinner, better penetrating result. (turns it into a "1lb cut" in Shellac lingo) Then it's nearly like water, and soaks in fast. Never had a problem like you mention.

    If it is the same stuff, you might have put on many coats till a layer was standing on the surface, then brushed it again before it was fully dry, causing the layer to remelt and crinkle up. Shellac doesn't cure, it just dries. New layers will "melt" into the older layers, you have to be careful not to damage underneath. But that should only apply if you have built up a LOT. Brush fast and light, never overbrush. I was spraying when I did a full Shellac finish for fear of doing that.

    Another possibility, you have a very old batch. There'll be a date code on the bottom, if it's getting near that, it may not dry fully or have other problems...

    Anyway, when it's the right stuff, good results are had by quickly brushing or spreading on with a small cloth ball or pad... wet it till it stops soaking in, don't try to put a layer on. Wait a half hour to hour for it to dry, go over it again. I usually do three, or even just two passes, it will slow down its "drinking" then you're there. Still should be little to no thickness on the surface. It will be soaked into the MDF, hardening and sealing the surface. Give it a day to dry fully, and a light surface sanding, and it's ready from there for whatever...

  8. #8

    Default Re: MDF Sealant Horror

    i use the white pigmented Zinser shellac all the time with no problems after i stir it with a drill attachment stirrer till it looks consistent. The clear and amber have done that crackling for me too a few times. on M.D.F. -masonite etc......

    works fine on wood though ..Why why why ??????? maybe brushes not pre soaked in denatured alcohol ? I know this was the case a few times because the shellac hates other solvents plus new brushes seem to have something on them .

    Gloves and steel wool worked well to fix the crackled cabs .

  9. #9
    Join Date
    Jul 2009
    Location
    Frederick, Maryland
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    112

    Default Re: MDF Sealant Horror

    I had a slightly different MDF Sealing issue, mostly a cost issue. I saw somewhere on the forum where a fellow memeber is building or has built a large 3 way in a very cool looking cabinet made out of MDF, lots of tricky angles on the top T&M section and a large box for the W. The post showed a bottle of MinWax Wood Hardener, sitting between the two huge cabinets and the end result looked great.

    So, I am in the last stages of my TriTrix TL build (figuring out how to put a finish on them that would register high on the WAF meter!) and have the cabinets all glued up and sanded and went off to get some of the wood hardener. I made a mistake and went to a small mom & pop hardware store and paid $13.99 for a bottle. I was surprised at how fast it seemed to evaporate and how fast the MDF soaked it up. It took one whole bottle to do one coat on one TriTrix TL cabinet. Mind you, I was putting it on liberally and the one cabinet I managed to get coated looked as good as what I had seen on this forum.

    If you use this stuff, forget using a roller of any type and don't use those super cheap disposable foam brushes! The roller has too much surface area and leads to serious product evaporation, the cheap foam brushes melt due to the high solvent content of the hardener. Lesson's learned the hard way! I'll be trying the glue/water mix on the next build for sure, sounds a lot cheaper and a lot less loss and waste! Dry time might be a lot longer, but a 10 oz. bottle of glue and 20 oz. of distilled water will only cost about 6 bucks and should cover a lot more surface area.

    There is a brighter side to this story though, my wife and I were in Home Depot recently and they had the same stuff for $9.00 a bottle. So I'm getting the other cabinet sealed and ready for primer and a few coats of high gloss black semi metallic hammer finished paint (Wife approved and selected!) I'll try to post some pics of the finished speakers once they are ready to rock!

    Also, I must say thanks to Curt for another excellent design and PE for making it one of the easiest systems in kit form to put together. This kit is my "jump back into the hobby with both feet" motivator, and I am officially back into it full force.

    Several of my neighbors have stopped in my garage/workshop to see what all of the noise and dust was about and are now eagerly waiting to hear the results. A few of them are interested in getting into the hobby now as well.

    Sorry for being so long winded...
    Remember, the outside of every silver lining is a cloud.

  10. #10
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    Oct 2005
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    Default Re: MDF Sealant Horror

    Quote Originally Posted by supermike View Post
    On the recommendation I found, I bought a can of Zinser Shellac Universal Wood Sealant for use on MDF prior to painting.

    Well, I applied the stuff, and to my shock and horror, as it started drying (which it does rapidly), it started developing crinkles or stress lines; the way the top-most layer of ice looks as it just starts to freeze. I let it dry over night, and then sanded. The sanding reduced some of the crinkles, but they're still there. I'd had to sand right down to bare MDF to get rid of these defects.

    Why did this happen?


    Did I not stir enought? How much stirring does it need? A couple of hours? A couple of days? This crap may've ruined my project.

    Wouldn't a sand, and reapplication take care of "defects?"

    Also, why not dilute the product some to see if that helps.

  11. #11
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    Mar 2008
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    Malvern, Ohio
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    3,416

    Default Re: MDF Sealant Horror

    Quote Originally Posted by rwrankin View Post
    I had a slightly different MDF Sealing issue, mostly a cost issue. I saw somewhere on the forum where a fellow memeber is building or has built a large 3 way in a very cool looking cabinet made out of MDF, lots of tricky angles on the top T&M section and a large box for the W. The post showed a bottle of MinWax Wood Hardener, sitting between the two huge cabinets and the end result looked great.

    So, I am in the last stages of my TriTrix TL build (figuring out how to put a finish on them that would register high on the WAF meter!) and have the cabinets all glued up and sanded and went off to get some of the wood hardener. I made a mistake and went to a small mom & pop hardware store and paid $13.99 for a bottle. I was surprised at how fast it seemed to evaporate and how fast the MDF soaked it up. It took one whole bottle to do one coat on one TriTrix TL cabinet. Mind you, I was putting it on liberally and the one cabinet I managed to get coated looked as good as what I had seen on this forum.

    If you use this stuff, forget using a roller of any type and don't use those super cheap disposable foam brushes! The roller has too much surface area and leads to serious product evaporation, the cheap foam brushes melt due to the high solvent content of the hardener. Lesson's learned the hard way! I'll be trying the glue/water mix on the next build for sure, sounds a lot cheaper and a lot less loss and waste! Dry time might be a lot longer, but a 10 oz. bottle of glue and 20 oz. of distilled water will only cost about 6 bucks and should cover a lot more surface area.

    There is a brighter side to this story though, my wife and I were in Home Depot recently and they had the same stuff for $9.00 a bottle. So I'm getting the other cabinet sealed and ready for primer and a few coats of high gloss black semi metallic hammer finished paint (Wife approved and selected!) I'll try to post some pics of the finished speakers once they are ready to rock!

    Also, I must say thanks to Curt for another excellent design and PE for making it one of the easiest systems in kit form to put together. This kit is my "jump back into the hobby with both feet" motivator, and I am officially back into it full force.

    Several of my neighbors have stopped in my garage/workshop to see what all of the noise and dust was about and are now eagerly waiting to hear the results. A few of them are interested in getting into the hobby now as well.

    Sorry for being so long winded...
    I believe you are talking about my Nightmare cabinets.



    I showed a bottle of the Min Wax hardener between them in the post that pic was in. I stated I was not very impressed with the stuff, especially the cost, because of how much it soaked in. The Nightmares are a medium sided cabinet and I used the whole bottle and still could have put on more. I know the idea of the stuff is to penetrate. I went over it with Shellac based bin 123 with several coats. I was concerned since I was using automotive base coat/ clear coat that it may be to hot for the shellac so I went over that with water borne automotive primer. I then put the base coat over that. Believe it or not When I put the clear coat over the base coat I still got some expansion in the seams that did not show up until about four hours after I sprayed them. Seems the clear coat must have bit clear through to the MDF and still expanded it. Its not bad but its still there.
    My next set I build if I paint them I am thinking about sealing the MDF with an epoxy sealer.
    http://www.star-distributing.com/smith/cpeswhy.html

    Then maybe a coat of epoxy paint.
    http://star-distributing.com/smith/hbepwhy.html
    I used these products on my water ski jump that I just resurfaced and I really liked them.
    If nothing they will be water proof
    Dave

  12. #12
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    Default Re: MDF Sealant Horror

    I also tried the minwax wood hardener. The MDF took coat after coat... In the end, I retreated to undiluted elmer's wood glue.

    If I slather glue over the entire surface of the cabinet and rub it in, it only takes one coat. I am generally ready to sand about 2 hours later...

    1 gallon of elmer's wood glue = $15 (This will last for many projects...)

  13. #13
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    Default Re: MDF Sealant Horror

    I've read of people using solvent based poly urethane. anyone have any opinions on that? I'm sure it would work just fine and IME it smooths itself out not too badly. I'd be more worried about what ever you're going to put on after actually sticking, be it primer or PVA glue for veneer.

  14. #14
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    Default Re: MDF Sealant Horror

    Quote Originally Posted by brianpowers27 View Post
    I also tried the minwax wood hardener. The MDF took coat after coat... In the end, I retreated to undiluted elmer's wood glue.

    If I slather glue over the entire surface of the cabinet and rub it in, it only takes one coat. I am generally ready to sand about 2 hours later...

    1 gallon of elmer's wood glue = $15 (This will last for many projects...)
    The wood glue probably would stop the paint from penetrating through to the MDF, but I would be concerned about how hard the glue dries. It may tend to be brittle. I suppose there is a fine line on thinning it so it penetrates and not putting it on to thick to avoid to much build up to make it brittle.
    Dave

  15. #15
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    Default Re: MDF Sealant Horror

    Please excuse the 'newbieness' of the following questions:

    So, what are the final results of sealing mdf vs not sealing? Does it make for a smoother surface? I assume it allows the paint to be applied and dried more evenly. But does it affect the feel or geography of the surface? I can see the benefit of sealing the edges, just wondering of the rest.

    I suppose I will need to try this the next time I get a project. It must be worth the effort since it seems popular to do.
    If dynamite was dangerous, do you think they'd sell it to an idiot like me?

  16. #16
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    Default Re: MDF Sealant Horror

    Quote Originally Posted by davepellegrene View Post
    The wood glue probably would stop the paint from penetrating through to the MDF, but I would be concerned about how hard the glue dries. It may tend to be brittle. I suppose there is a fine line on thinning it so it penetrates and not putting it on to thick to avoid to much build up to make it brittle.
    Dave
    I would not have any concern with the Elmer's wood glue being brittle. I put two coats on the cabs I'm working on last week, not in preparation for painting, but for veneering. Although I'm not painting, the undiluted glue settled into a smooth surface and was not brittle. I used a cheap foam roller and it seemed to seal quite well.

    ---------
    BTW, the Elmer's white glue worked quite well for veneering (iron-on method). It has a lower re-activation temperature than Yellow Titebond I or II, and there is no expiration timeframe for re-activation. Furthermore, it can be re-activated a number of times.

  17. #17

    Default Re: MDF Sealant Horror

    I've used a 50/50 wood glue/water mixture on 4 mdf enclosures now (that I then painted), and it worked extremely well.

    It sealed the mdf thoroughly, sanded to a glass-smooth finish, and seemed to be an excellent surface prep for primer.

    On my center channel, I tried shellac. Didn't work as well. Sanded terrible compared to the wood glue... balled up and came off in places.
    Form does not follow function
    Form is simultaneous to function

  18. #18

    Default Re: MDF Sealant Horror

    Quote Originally Posted by davepellegrene View Post
    The wood glue probably would stop the paint from penetrating through to the MDF, but I would be concerned about how hard the glue dries. It may tend to be brittle.
    Dave
    Not an issue. I used 5 coats of wood glue/water on my SR71's, and never had a problem.
    Form does not follow function
    Form is simultaneous to function

  19. #19
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    Default Re: MDF Sealant Horror

    Someone once pointed out that anything water based could cause the mdf to swell. This is the reason that I use the glue undilluted.

  20. #20

    Default Re: MDF Sealant Horror

    Quote Originally Posted by the kid View Post
    Please excuse the 'newbieness' of the following questions:

    So, what are the final results of sealing mdf vs not sealing? Does it make for a smoother surface? I assume it allows the paint to be applied and dried more evenly. But does it affect the feel or geography of the surface? I can see the benefit of sealing the edges, just wondering of the rest.

    I suppose I will need to try this the next time I get a project. It must be worth the effort since it seems popular to do.
    Yes, you must seal the mdf prior to painting. Edges and surfaces.

    Here's a couple pics of my Tritrix's... wood glue/water to seal (2-3 coats), then sand, then primer, then more sanding, then paint... these are now almost a year old, and still look excellent...



    Form does not follow function
    Form is simultaneous to function

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