# How do you seal MDF to do a lacquer finish?



## Mooble

I want to make an MDF enclosure, but I want to put a black lacquer finish on it. The lacquer part is not hard. I just need a glossy black paint and a couple of clear lacquer coats on top of it. The difficult part is getting a perfectly smooth surface on the MDF to do the glossy black coat.

What do I use to seal the MDF? Regular sanding sealer won't work. MDF absorbs it up like a sponge. I suppose I could keep doing it until it stopped absorbing but that would take forever. Is resin thick enough not to be absorbed? I don't really want to use something like Bondo over the entire box. 

Suggestions? What will seal MDF that, once sanded, will leave a perfectly smooth surface?


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## Rudeboy

To waterproof MDF, I've used resin, thinned with 4 parts acetone and catalyst based on the total volume. Slather on a few coats and it soaks in nicely. That might let you use a sanding primer like you would on any non-porous surface. You'd have to test it first.


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## GlasSman

Whatever you do before hand use a nice primer.

I've used furniture laquer in a can on some MDF shelves and got a nce smooth and solid finish.

With clear it would been even better.


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## GlasSman

I used Rustoleum Painters Touch Furnture LaCquer.

3 or 4 light coats and I fine sanded the rough spots.


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## Illusus

This thread, from another forum, covers MDF priming and sealing _very_ extensively. http://www.diyaudio.com/forums/showthread.php?s=&threadid=100520&highlight=

...and here's one about getting that piano black finish
http://www.diyaudio.com/forums/showthread.php?s=&threadid=83141&highlight=sealing+mdf


(hope it's cool to link to another forum. I could have written my own tutorial here but Shin said it better... and I'm lazy)


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## iskone

I've read that oil based paints/lacquers don't adsorb into MDF.


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## GlasSman

iskone said:


> I've read that oil based paints/lacquers don't adsorb into MDF.


Yes...and thats what you want.

MDF is a sponge with water based paints.

A good primer will seal the deal.


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## Ge0

I went through a ton of effort in the past to give a home MDF subwoofer project a "piano black laquer finish". Something to beat a laminat finish the old fashioned way...

This looked awesome for a few years. But, eventually the MDF absorbed moisture and swelled. I ended up with hairline cracks in the finish.

Unless you carefully treat the MDF to be moisture resistant somehow you'll end up with something similar. Take time and heed others advice.

Ge0


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## Illusus

I always seal inside and outside for that very reason and, as an added bonus you get CLD properties.


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## gijoe

Old thread, but I found a helpful hint for this.

I have been making some very simple mdf rings so complete my door project. They aren't really grills, but they go on the front of the speaker to give it a more finished look.

I cut out the rings and rounded the edges. They looked perfect. Then I started to seal up the raw edges. I tried a couple different kinds of primer, several coats of each and obviously the MDF just sucked it up. Then I decided to try using glazing putty. This proved difficult. No matter how thin I spread it on I'd have to sand and sand to get everything smooth. By the time I sanded everything smooth I ended up with low spots where I'd cut into the MDF which is a lot softer and sands much quicker.

Frustrated with the time it took with such a simple project I looked for a new idea. I found that if you thin yellow wood glue with a little water, 3 parts glue 1 part water, you can brush on a really nice thin coat. You can easily wipe off the excess if you get runs. After it dries for a couple hours, you can apply another coat (if necessary) or hit it with a coat of primer, then paint.

I don't have any experience yet on how long this solution will protect the MDF from moisture, but I don't foresee any issues in the near future. 

Hope this saves someone the several hours I lost with the damn glazing putty.


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