MDF Finish

[bjackson]

I've finished one of my enclosures pretty much, but it's pretty umm...crappy looking. Lot's of dried glue, screw holes, etc. (The screw holes are countersinked atleast). (The dried glue was brushed off before drying so it's just stained now).

I need to finish it to look decent. I really don't have a preference at this point. I was thinking maybe using bondo, or woodfiller to fix it. Or maybe using woodfiller, and sanding everything and putting a thin piece of nicer wood on top, but I was worried about diffraction off the front baflle if it was no longer flush.

ANY and ALL suggestions welcomed and appriciated. I have one week before I start working on them again (damn college, taking all of my time away from my precious audio equipment)

 

[bjackson]

BTW, the box is 48(H)" x 18" x 18" outside dimensions. My budget is limited, but I'd rather wait and have quality than do something that is cheap and crappy.

 

[ultrachrome]

I don't know if what you fill the voids with is that critical. I'd just go with whatever your hardware store recommends.

So I take it you flush-mounted the drivers on the baffle? If you were going to veneer, I think you'd usually cut the driver holes after you veneered it as it is difficult to trim the veneer around the driver holes recesses.

If you want the wood look, you could veneer the sides, and then slap a second layer of real wood on the baffle and recut the driver holes in the same locations. Then round over or bevel the edges of the baffle.



I've also used spray-on aerosol bedliner which looks really good but for a speaker that size, I'd save it for just the top sides and front as it can get pricey. Use whatever you want on the back. Unlike what you might think, the rough texture does not really hide surface flaws so if you go this route, smooth your surfaces well. A good palm sander makes easy work of this.

 

[audio-kraut]

Filling, sanding, filling, sanding;
priiming, sanding # 220
filling whats now visible;
sanding, # 220 or above;
priming and sanding # 220

first coat paint, varathane colours in plastic;
sanding # 400
second coat, same paint, sanding # 400
thirs coat.

Between each sanding and coating wipe with tack cloth.
Gives you piano paint like finish. I had coated mine five times with finish paint. Looked excellent - and that night my shop burned down

The truckbed liner can look great - but some prep is needed. You have limited time to work it, as it is epoxy based and contains a hardener. Should only be used in well ventilated areas - i.e. out doors.

 

[rcavictim]

Just a word of caution about the Varathane Colors in plastic. I have been using white shellac diluted with alcohol to seal all my MDF projects prior to applying paint. The varathane says not to use shellac as an under sealer. I guess it won't stick.

 

[richie00boy]

With MDF is important to seal or use the correct primer. MDF soaks up paint. I use proper MDF primer, but you can seal first with a 50/50 water/PVA mix to seal, then prime with normal wood primer. However make sure you fill any nicks or screwheads beforehand. Just use car body filler, but you can get dedicated wood filler that mixes up the same way.

Get your finish as good as possible before any priming, then sand between each 2-3 coats with 800 grit wet and dry paper to get a nicer finish. Do that a couple of times and your ready for topcoat.

 

[Paradise_Ice]

Another thing you could do after you have smoothed the exterior off, you could cover it in a textile fabric, there are so many to choose from these days, i have a wee hobby and its covering everything in a sued velour type grey a few cans of spray glue which has amazing strength and it will hold almost anything down.

This give a nice matted finish if done well, so pratice is the key.

This can give a very nice tactile finish that everybody wants to touch and rub their hands against all so its very cheap to do.

Adding a vaneer is good to but its very time consuming and can be costly depending on the vaneer quality and type.

i think maybe its the PVA i use but mixing it 50/50 with water makes its to weak to seal MDF.

Using the car body filler is also an excellent method but also takes time and skill.

 

[Cal Weldon]

If you like a texture coat, this is what I used for the selenium coax boxes. It's "Accents" by Rust-Oleum. This is the "Stone Creations", black granite. Each can did 15 square feet or one can per cabinet in this case.

 

[Cal Weldon]

This is the completed box

 

[dhenryp]

One "trick" to finishing MDF is to seal any exposed edges. It is very absorbant otherwise and will soak up many many layers of paint. I take some ordinary yellow carpenters glue (take your choice, I often use Titebond) and dilute it with water ~ 50%. Put this on the edges before doing any other filling or priming.

I've had good luck with Bondo - easy to sand and dries very quickly. The first coat will sometime shrink and require a second coat for a smooth, flat finsh.

If you have the patience and stamina you can get an excellent gloss finish with plain old Rustoleum Spray Lacquer. As Audio-Kruat said, be prepared to do quite a bit of sanding. Spray on textured paint still needs good prep but the actual painting will go much quicker.

 

[RCBandwidth]

Textured Finish

I finished these with Rustoleum black granite texture,with very good results.I would recommend this for those who need to cover severe blemishes. RC

 

[Paradise_Ice]

If you like a texture coat, This is the "Stone Creations", black granite. Each can did 15 square feet or one can per cabinet in this case.

I have used this crackle paint in the past, its a very nice but it takes awhile to dry out fully.

There is a paint called Hammerite, i dont know if this is the type of paint or the company that sells it, but its an extremly tough and glossy paint, very Toxic too.

 

[bjackson]

Would you guys recommend bondo, or wood filler if I was to sand it down multiple times, and then apply paint to it, to give it a glossy shine.

Now this varathane, what exactly is it, just a type of paint, or is it different from others in a substantial way?

Thanks!

 

[dhenryp]

In my experience, Bondo works fastest, shrinks least, and provides the smoothest finsh.

 

[Exhifi]

You can trim the dried glue with a cabinet scrapper, about $15 at any woodworking store/online, and they are good to have if you decide to veneer.

The glue water mix is the way to go for sealing the MDF.

If you want a black lacquer or "piano black" type of finish, clean up the cabinets, sand, scrape, etc...Seal the MDF, prime it and paint it black. a black laquer is good, but almost anykind is fine. sand with 600 grit, softly, and then apply coats of clear lacquer, lightly sanding with 600+ grit in between. The lacquer dries fast, so you can finish the whole thing in a day. The more coats of lacquer, the better it looks. Kinda like clearcoating a car.

By the way, the sanding between coats is done really softly, you aren't trying to take anything off, just haze up the previous coat.

I actually wax the last coat of lacquer with carnauba ONLY wax. No silicones.

You can buy the gloss lacquer in spray cans if you want or just paint it on, but spraying is probably best, given the size.

You can also just do this to the baffle and then veneer the sides, etc...

 

[Cal Weldon]

its a very nice but it takes awhile to dry out fully.

Ya, no sheep dip. Took mine close to a week to become tack free. Warm room too.

There is a paint called Hammerite, i dont know if this is the type of paint or the company that sells it, but its an extremly tough and glossy paint, very Toxic too. [/B]

That's another option but has a much different appearance. Seems to be quite durable, very hard finish as you mentioned, more so than the stone creations which is a lot like truck bed liner.

Cal

 

[Zene Gillette]

Hi ... You'll never get that big box (the little ones are easy) to look good by filling, painting etc. Bed liner commercial spray will do it if you like the grunge club look.
After trying to get mdf to look right dozens of times I found the only solution for me was to skin the panels with 1/4 " hardwood ply. Lots of Liquid Nails and a little work and you can have a great looking box.
Veneering is not the answer because it follows any imperfections and is way too expensive. Zene

 

[ShinOBIWAN]

After trying to get mdf to look right dozens of times I found the only solution for me was to skin the panels with 1/4 " hardwood ply. Lots of Liquid Nails and a little work and you can have a great looking box.
Veneering is not the answer because it follows any imperfections and is way too expensive. Zene

Did you seal and fill the MDF correctly or rather what did you use to do this?

I agree that any joints on unsealed MDF will ALWAYS show up a few days after spraying. But correctly sealed using a 40/60 water/PVA mix, I've never had any joints show again on my work. I seal all edges once then go over the entire box after that's dried, sand it all and repeat once more, with a final light sanding. Then just apply MDF primer and proceed to finishing coats.

The sealer you use is also incredibly important. Get something that's non porous. I use a two part wood sealer for most work or sometimes two part automotive for larger gaps. I've found that the wood filler that you find in chalking guns is usually useless.
To be honest though you really shouldn't need any filler if your joints are good, just sanding and then sealing.

It is a hard lesson to learn, especially if you've invested many hours into construction only to find that you've got to either rebuild or strip back.

 

[nerd of nerds]

you could always cover em in that fake fur stuff

actually, seeing as my painting skills suck (something i'm working to improve), i'm just going to cover my hi-vi b3n boxes in lime green fake fur stuff...

i'll post some pics when i'm done....

 

[GordonW]

With MDF is important to seal or use the correct primer. MDF soaks up paint. I use proper MDF primer, but you can seal first with a 50/50 water/PVA mix to seal, then prime with normal wood primer.

So, just plain 50/50 Elmers white glue or wood glue, applied with a brush and rubbed smooth with a damp rag should work, right? I'd thought about doing this, but hadn't gotten around to doing it yet.

I'd think the PVA/water mix should also "harden up" the surface of the MDF a bit, making it a bit more impervious to bruises, dinks and chips, right?

This could come in very handy, whenever I get around to building my DIY JBL 250Ti clones... was thinking of doing them piano black, like the Jubilee 250Tis...

On a similar note- has anyone tried using plain old fiberglass (polyester) resin, brushed over MDF and sanded smooth? Or would that be prone to cracking? That'd certainly fill the seams and end-grains of the MDF...

Regards,
Gordon.