MDF finnishes.

[peterpan]

I will like to keep the colour of raw MDF on my speakers, what do I seal them with?

[BigguyZ]

A lot of finishes will darken MDF and give it a "wet" look. You may want to try a water based poly, which tends to not darken wood as much, but you may have issues with the MDF swelling. I would run a few test pieces and try out a finish or two until you get what you're looking for.

[numberoneoppa]

Epoxy?

[baniels]

A lot of people use wax paste to seal their raw MDF router tables to keep out moisture. May serve the same purpose here. Nothing will tell you better than some tests on scraps, as bigguyZ said.

[---k---]

MDF is soft and easy to damage. If you want the natural look, I would suggest Minwax Wood Hardner. It is semi-clear, it will give the box a darker wet look like stated above. But, it penetrates about an 1/8" and hardens the wood. I did some tests and had photos in a thread here. I think this would give you more durability than a straight clear poly.

http://www.htguide.com/forum/showthread.php4?t=32292&highlight=minwax

[blue934]

how about a couple coats of 50/50 water/white glue? it might make it slightly darker but not much and it does harden the surface.

david

[Txgrizzly]

also make sure you round the corners as MDF is susceptible to chip out at the corners if bumped....

[jcain]

Unprotected mdf is never a good idea I would suggest a high grade primer and paint.
Personally I use automotive paint you can have a color match done as i did with my HIVI al. mag. cones it has a realy nice look and a little pearl added to the clear realy stands out. Of coarse this depends on weather you have the knoledge and tools to do it. I am still working on mine and will post som picts when I finnish them. Good luck

[BigguyZ]

I would think the glue/ water mix would still cause swelling, but the wood hardener is a good idea.

But I wouldn't buy the Minwax product, as it's $$. Just make your own. Get some acetone from HD or Menards or Lowes, about $16 for a gallon. Go to your local hardware store or window repair shop, and usually they'll give you their plexiglass scraps. Then just break up the plexiglass as finely as you can, and dissolve in the acetone. The mixture is commonly called plexitone, and is basically the same as Minwax wood hardner. You can make thick or thing mixed, depending on your needs.

I know some people also use this as a finish (especially for pens), and some use it to stabilize wood (again, I use it to stabilize wood for pens- my other hobby).

I'd try some tests myself, but my shop is in shambles due to a move from a basement to a garage.

[mtmpenn]

How about one thin coat of seal coat (dewaxed shellac with a very mild amber tint, used to seal the mdf) followed by water based poly?

That should only cause a very minimal color change. Definitely test whatever

Personally, I would go with veneer or paint. Both can be used successfully on mdf (I think veneer is much easier than paint and some inexpensive veneers can look amazing).

[Solid-State]

I posted this else where but it might be of interested regarding painting, sealing and gluing MDF etc.

Gluing, Sealing and finishing MDF for Paint and Veneer

Post HiroPro on Thu Apr 29, 2010 6:30 am
I'm curious as to what products to use working with MDF. What is the best glue to use to bind joints. Should I use a biscuit? How should I prep the MDF at the joint. Sand it? As for glues for veneer the local hardwoods shop said use epoxy. I mentioned the iron on glue stuff DIY seem to use but he had no idea what I was talking about and said "no no use epoxy" but this guy knows nothing about MDF substrate. I have heard so many varying opinions on the topic that I'm rather lost as to how to finish the cabs LOL. It seems very little is known in the wood working community how to work with MDF and they all stick their noses up and use baltic birtch. I found some great posts on the shop bot forum regarding working with MDF.

"Sherwin Williams "Promar" E-Z Sanding Lacquer Searler B44FT8" seems to be popular as a sealer for Lacquer top coat.

This seems to be the best way to apply it.

To get the best results, I suggest this procedure and you will get good results and as you refine it you will get perfect results.

1. Sand all edges with 150-180g
2. sand all edges with 200-300g
3. primer using a lacquer based sanding sealer
4. sand whole thing with 300g
5. add another coat of sanding sealer and another if needed.
6. paint as usual...

By using that process you will get a bullet proof finish. Heres why...

first you are sanding to remove any machining marks, then you are "burnishing" with 200-300g.

What this means is you are using the micro dust to seal the edges as you are sanding.

Then by adding the sanding sealer you are in effect making a surfboard type of finish, the sanding sealer soaks into the pores making it one solid surface."

http://www.talkshopbot.com/forum/showthread.php?t=9830

http://www.talkshopbot.com/forum/showthread.php?t=8334#POST68351

And this is an interesting post

http://www.contractortalk.com/f8/has-anyone-ever-heard-using-lacquer-primer-19412/

The top coat is Porter's Glyptex High gloss oil.

This stuff I can easily source.

http://www.plastikote.com/products/Primer/Sandable-Primer.html

[Solid-State]

I found some interesting products and I wonder if others have used it with MDF

This looks like a potential FANTASTIC sealer for MDF

http://www.smithandcompany.org/mwp/index.html

They also make a glue in which the marketing material specifically mentions speaker cabinets.

http://www.star-distributing.com/smith/differences.html

Looks like great product.

[JonP]

How about one thin coat of seal coat (dewaxed shellac with a very mild amber tint, used to seal the mdf) followed by water based poly?

That should only cause a very minimal color change. Definitely test whatever

Personally, I would go with veneer or paint. Both can be used successfully on mdf (I think veneer is much easier than paint and some inexpensive veneers can look amazing).

I've played around a fair amount with Zinnser's Seal Coat shellac... including as a finish on MDF. It does darken it a bit, especially after several layers. You could try "clear" or "blond" shellac, but be aware that the regular shellacs aren't fully dewaxed, and other finishes may have a problem coating them. The Seal Coat product is dewaxed, and dewaxed shellac is compatible with just about everything.

I usually use it cut 50:50 with alcohol.. that takes it to 1lb cut, sometimes even more like 3:2 if I want it to soak deeper. Soak in as much as it will take, let dry for 30 min, do it again 2-3 times or till it stops soaking up more. Then let it dry a day or two.

You get a hardened surface, (at least when the shellac is not old) with it soaking in a moderate amount. Sands very easily and true. I nearly always use it for this before veneering, helps with it sanding down smooth.

I did a test piece for the heck of it, where I kept adding layers, sanding, etc... it actually looked pretty good for bare MDF. You can buff up the shellac pretty nicely. Though I'd agree, for a more durable surface you'd probably want to cover it with poly or something.

Some of the other ideas sound good, maybe even better if you want it to stay as light as it is now. Sounds like you have some research to do with scraps! :B