MDF finishing techniques

[JonJT 10+ year member]

I need to finish 3 raw MDF boxes and I want to do them in black gloss. First I would like to know how to fill in the baps? Would bondo work well for this? Secondly, what kind of paint do I need to use to get my desired finish. And Would paint brushes or rollers work better?

Thanks.

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[JonJT 10+ year member]

Also, I'd like to cut a nice smooth radius on all the edges of my boxes. Does anyone have a recommendation for a radius cutting bit that won't weaken the but joints in my enclosures too much?

 

[AK SloPok 10+ year member]

For a smooth finish bondo is great but I would use a fiberglass strand reinforced version to help with the "gaps". Gloss black will take a ton of time to get smooth, better going with a semi gloss or flat that wil not show the box imperfections. You can get a good finish with an can of Krylon and a small roller, it has some self leveling abilities, for the best finish though you will need to wetsand and buff to a gloss.

You can round the edges a bit with a router. It will take a steady hand on a built box but it is possible. Something like a 1/4 roundover bit or similar...

 

[JonJT 10+ year member]

For a smooth finish bondo is great but I would use a fiberglass strand reinforced version to help with the "gaps". Gloss black will take a ton of time to get smooth, better going with a semi gloss or flat that wil not show the box imperfections. You can get a good finish with an can of Krylon and a small roller, it has some self leveling abilities, for the best finish though you will need to wetsand and buff to a gloss.
You can round the edges a bit with a router. It will take a steady hand on a built box but it is possible. Something like a 1/4 roundover bit or similar...

When I say gaps, I meant edge imperfections due to panel's not being cut exactly to size. Its hard to get tolerances smaller than 1 tenth of an inch without thousands of dollars of wood working equipment. Especially when cutting large 4X8 MDF or HDF sheets.

I was hoping I wouldn't have to wet sand the boxes for a gloss black finish. I've wet sanded aluminum pipes before and a 12 inch long 3 inch OD tube took me 3 days to shine. I really, really don't have time to wet sand three large enclosures. Whats the norm to get a semi gloss finish? Sanding to around 800 grit and a few coats of Krylon black with a clear coat? I also have a roll of Mahogany Veneer in the garage. Thats another option but I didn't really like how the other speakers I did came out. Its the cheap Parts Express stuff that peals easily. In order to get a good finish with the cheap veneer, I figure I'd have to sand as if I was going to do a gloss black finish.

And as for the rounding, I planned on getting a router table and bolting my Ryobi to it. Should make cutting a radius easier, especially if I make some supports out of scrap wood.

 

[kickerlivinloud 10+ year member]

For a good glossy finish I'd put down several layers of primer and the paint its self. 3 of primer and at least 4 of the paint then I'd sand with 600 grit paper. You might want to wet sand with it but it won't be to bad. Now if you want a really good finish I'd go up to 2000-2500 grit.

As far as filling the gaps, I personally use drywall compound. Just regular mud or maybe even 90. I've never tried a glossy finish with the stuff but I don't see any reason why it would cause any problems.

Its hard work doing though, trust me... Took me over a week to get this far...

Its well worth it but it takes lots of work. If you have any questions feel free to ask..

Jon

 

[JonJT 10+ year member]

I think I'm just going to cover them with the Veneer I've got in the garage. Its going to take too much time and money to get the black gloss finish I want. Thanks though. Next time I build some speakers I may give this a try.