[Whitebread]

I'm in the process of designing a subwoofer for my house that will be built out of MDF. I've been doing a bit of research on finishing MDF and if anything I've become more cognizant of my own ignorance in the matter.
I'd like a glossy piano like finish and so far I've picked up on the following:

First, the box needs to be sanded to about 320 or 400 grit to ensure flat surfaces.

Next, some kind of body filler like substance should be applied to reduce porosity and fill gaps. I've seen people coat the entire box in bondo, focusing especially on the cut or machined surfaces. After this the box then needs to be sanded smooth up to maybe 400 grit?

Next, some kind of primer needs to be applied. What kind? One person recommended a Polyvinyl Acetate based primer. A prodigious number of coats need be applied with wet sanding in between. Correct?

Next, the paint layer needs to be applied. Does anyone know what base paint should be used? Latex or Urethane? Also, matte, flat or high gloss? Three to four coats with with sanding in between (what grit)?

Finally, the clear coat/sealer. Same deal here with multiple coats and wet sanding in between (again, up to what grit)? And I do believe an automotive buffing compound would work well to shine the surface after the final coat is dry?

Does this process sound correct to you guys? Is there anything I should change? Keep in mind I do not have a spray booth or a gun, I'd be hand painting the box in my garage with brushes. I'd also like to keep all the paint supplies at 100 dollars or less. Also, can I get away house paints and products or are automotive paints, primers and clear coats/sealers required? Finally, does anyone have any recommendations as to exactly what products I should buy?

Thanks!!

 

[fatcat28037]

Oh good........that's SUB as in woofer, not marine, I was worried until the 2nd sentence.

 

[Whitebread]

I eliminated the shorthand to eliminate further confusion. Do you have any experience finishing MDF?

 

[keyid]

sounds about right

bondo is good for covering screw holes and fixing edges which may have bad imprints, dont get the stuff on flat surfaces cause you will need to sand it out. Use sanding blocks to get flat surface. Also good to bondo the exposed cut sections as it will soak up moisture and can expand.

I used like to use killz for primer using brush wil couple 3 - 4 coats.

Then wet sand with high grit sanding blocks, use little water as possible cause you want the water mixtures to fill up any pores to get a smooth surface. Then I take it to a paint shop to get it done, imo its worth the money. If not, then spray paint it couple times then wet sand it again until you like it, for final sand I like to use a paper bag.

 

[Omega]

MDF is great for being cheap and non-resonant. But it is a royal pain to work with. Wear an N95 mask when you cut/sand MDF--often MDF is made using a formaldehyde process (formaldehyde is quite toxic, especially when inhaled on dust).

MDF is REALLY porous. You'll save yourself pain if you coat with primer until it actually DRIES on the surface, rather than being sucked in. Then the rest of your plan sounds ok. The key to a piano finish is either i) taking it to be professional done (by far the low-effort option) or ii) an iterative process of wet sanding - painting.

Honestly, if you are making a subwoofer, and you want it to look good, consider foregoing the MDF at all and make your (heavily braced) box from plywood or birch...or birch.

 

[Omega]

The best example of DIY MDF finishing I've seen is right here on Head-fi:
http://www.head-fi.org/forums/f6/pos...ml#post5872841

 

[Whitebread]

Quote:

Originally Posted by Omega /img/forum/go_quote.gif MDF is great for being cheap and non-resonant. But it is a royal pain to work with. Wear an N95 mask when you cut/sand MDF--often MDF is made using a formaldehyde process (formaldehyde is quite toxic, especially when inhaled on dust). MDF is REALLY porous. You'll save yourself pain if you coat with primer until it actually DRIES on the surface, rather than being sucked in. Then the rest of your plan sounds ok. The key to a piano finish is either i) taking it to be professional done (by far the low-effort option) or ii) an iterative process of wet sanding - painting. Honestly, if you are making a subwoofer, and you want it to look good, consider foregoing the MDF at all and make your (heavily braced) box from plywood or birch...or birch.

Is MDF really that bad? And is plywood or birch really that resonant?

 

[fordgtlover]

There are a few threads over at diyaudio including this one that might help.

 

[iriverdude]

MDF is most common material for subwoofer bracing, just make sure it's all sealed up and joins are airtight too. As for piano finish that is pretty hard I'd just paint in matt or satin black. Not gloss.

 

[AndrewFischer]

Shiny piano black finish on MDF is going to be difficult with a brush.

How about black stain on an iron-on wood veneer? You could put a gloss finish on it. Might be able to do that and stay in budget. In any case you should be looking on a speaker builder message board.

 

[cyberspyder]

Sealing MDF is primarily done with wood sealer. Other than that, primer it, with a light black coat to highlight the imperfections, sand, and primer again. Lightly sand, then apply first light colour coat, wet sand with 600 grit and apply colour coat again. Make sure to increase the grit everytime you sand, and on the LAST coat, DON'T SAND.

***USE A TACK CLOTH OR AIR COMPRESSOR TO BLOW ALL THE DUST OFF FROM SANDING***

After the colour coats, you can start applying the clear...as many coats as you want. Just remember to make sure each coat DRIES THOROUGHLY before the next coat.

 

[Whitebread]

I'd be fine with a black satin finish. The piano gloss finish would be nice but I'd rather not spend 5 years trying to finish this thing.

And cyberspider, I recognize that woman........

 

[Whitebread]

Quote:

Originally Posted by AndrewFischer /img/forum/go_quote.gif Shiny piano black finish on MDF is going to be difficult with a brush. How about black stain on an iron-on wood veneer? You could put a gloss finish on it. Might be able to do that and stay in budget. In any case you should be looking on a speaker builder message board.

How would I go about applying a "black stain"? Same process without the glossy paint and clear coat?

 

[Whitebread]

Quote:

Originally Posted by Omega /img/forum/go_quote.gif The best example of DIY MDF finishing I've seen is right here on Head-fi: http://www.head-fi.org/forums/f6/pos...ml#post5872841

I only see a bunch of amps.