Anyone ever try Minwax Wood Hardener to seal mdf?

[djg]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

My high school art teacher called it "defying the medium", trying to do something that just won't work. I have one pair of mdf speakers that I painted. I used Rustoleum stone texture paint, over Zinsser shellac sealer. No cracks yet, but that is really thick stuff. Small boxes, too. I expect them to eventually show the seams.

Consider veneer, or formica if you want a solid color look. That's my 2 cents.

BTW, always enjoy your builds.

[jonpike]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

I used Elmers... I sand afterward. Sanding is a long and tedious process after gluing in this way. I confess that I haven't used dewaxed shellac but it does sound like it has its benefits. I wonder how many coats it would require on end grain....

FWIW: I have pretty much stopped using MDF due to the laborious nature of the process.

What could help with sanding like this is to make a big sanding board... get a 6"x48" #100 or #120 sanding belt, cut it two equal length strips (but cut out the overlap, it's thicker) and put them down on a nice flat board of MDF. Now you have a flat block to slide box faces back and forth on, lapping them flat.
This avoids rounding edges and other problems you might get when hand or orbital sanding a large area.

I read many suggestions on the Zinnser Seal Coat (dewaxed) shellac for sealing MDF, what is suggested is to cut it 50:50 with denatured alcohol, then you have a thinner and more penetrating mixture. I get a brush and slather on as much as will soak in per coat. Let it sit for an hour or so, lay on a second. Maybe a third in another hour, maybe another. When it stops soaking in significantly, you're done. Let dry for a day or two, and sand a little. You can keep going, sanding between layers, and you'll have a pretty hard, flat surface. Go to the undiluted stuff, for faster buildup. This could be a solution for all those guys who never finish their bare MDF speakers... it doesn't look all that bad... ;)

As always, new, recent date code shellac, keep the lid on the main container to keep moisture from getting into it, (I pour some into another sealable jar for mixing) ditto for your alcohol supply... and it should dry fast and hard.

[waynew]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

Aaron Hero had a nice process on how to make MDF not show seams, and it involved using a Halogen light as a heat source and an old vacuum motor to push air inside his cabinets to dry them out. Personally, I have found that the only way to not get seams that show is to use a high build primer, and wait it out. Once the seams show up, then sand and put another coat on. This can take a couple of weeks, so patience is the the name of the game. After that, you play the same game with the color coat. MDF is a bear!

YMMV~!!!!!

Wayne

[gregrueff]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

I wonder if coating the speaker with fiberglass resin, like you are doing with the glue would work better. This might bridge the movement enough. The only thing I could see happening with enough expansion it could crack the resin.

I am in the process of finishing up a speaker doing just this.

It is MDF, sealed with a dinky water based paint on the inside and covered on the outside in a blackened, twill weave fiberglass with polyester resin. It looks like carbon fiber and is pretty darn slick.

But when I talk about this project in years, you will understand how tedious and stupid it has been. (There was considerable slacking involved too.)

Although I am quite convinced it is the most solid, inert box I have ever and will ever build. The knock test reveals a very high frequency resonance. And the composite strength of the fiberglas and resin has convinced me no amount of moisture pickup is going to have enough force to deform the seams. Just compare the base modulus of MDF against polyester resin- before you even factor in the fiberglas contribution to the composite. Magnitudes of difference.

I have just finished sanding the whole thing smooth with 60 grit. Now to spray on a nice high gloss finish. Once the whole thing is finished I intend to post pics with a full report.

Greg

[davepellegrene]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

I am in the process of finishing up a speaker doing just this.

It is MDF, sealed with a dinky water based paint on the inside and covered on the outside in a blackened, twill weave fiberglass with polyester resin. It looks like carbon fiber and is pretty darn slick.

But when I talk about this project in years, you will understand how tedious and stupid it has been. (There was considerable slacking involved too.)

Although I am quite convinced it is the most solid, inert box I have ever and will ever build. The knock test reveals a very high frequency resonance. And the composite strength of the fiberglas and resin has convinced me no amount of moisture pickup is going to have enough force to deform the seams. Just compare the base modulus of MDF against polyester resin- before you even factor in the fiberglas contribution to the composite. Magnitudes of difference.

I have just finished sanding the whole thing smooth with 60 grit. Now to spray on a nice high gloss finish. Once the whole thing is finished I intend to post pics with a full report.

Greg

That's basically how a boat's made. I bet that took a lot of work. Can't wait to see them. I plan on trying the resin method, when I do another painted cabinet.
Dave

[bobhowell]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

Aaron Hero had a nice process on how to make MDF not show seams, and it involved using a Halogen light as a heat source and an old vacuum motor to push air inside his cabinets to dry them out. Personally, I have found that the only way to not get seams that show is to use a high build primer, and wait it out. Once the seams show up, then sand and put another coat on. This can take a couple of weeks, so patience is the the name of the game. After that, you play the same game with the color coat. MDF is a bear!

YMMV~!!!!!

Wayne

Here you are drying it out before finishing. So, little movement after finishing. De-waxed shellac holds out moisture better from my readings. Also, other finishes adhere better. At best, finishes slow moisture transfer, not stop it. I have never read just what that means thought. Keep the speakers in an air conditioned/heated room and you will miss the extremes that tear them apart.

[davepellegrene]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

Here you are drying it out before finishing. So, little movement after finishing. De-waxed shellac holds out moisture better from my readings. Also, other finishes adhere better. At best, finishes slow moisture transfer, not stop it. I have never read just what that means thought. Keep the speakers in an air conditioned/heated room and you will miss the extremes that tear them apart.

I have used diluted white pigmented shellac on four speaker builds inside and out. Then sprayed with automotive paint over top. They eventually showed seams. I think over time the MDF draws moisture and expands. Doesn't take much to show a seam on high gloss paint. At my link below has pics of all my builds except two subs. The Nightmare set I sealed with the Minwax hardener, then let them sit inside for a month, then primed with shellac, then waited a month, then painted. Still showed some small seams that were not visible through the time they sat.
Dave

[lunchmoney]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

Brian, I have to say that overall the 2:1 mixture of Elmer's wood glue to water was terrible.

Too thick to spread into a nice even coat, and a real pain to sand... lots of hardened "drip" shapes.

I made do though.

I can't imagine how you were able to use undiluted and get a smooth finish

Definitely going back to a 60:40 ratio next time.

[rtkelly]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

Greetings;

Have any of you guys tried MDO plywood? I have some porch speakers cut out but, I haven't assembled them yet. It appears to be sturdy enough, sometimes used for concrete forms, I just don't know how stable it is. If no one has any experience with this material, I will post what experiences I have with it as I progress. TIA.

Rollie

[davepellegrene]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

I think it is controlled test time.
I am going to make up some right angle test pieces and glue them up with Tite Bond II. Then seal them on all sides.
So far I have;
Yellow wood glue, mixed 60/40. Is the 60 water? Does it matter which type.

Shellac, I have the Bin 123 white pigmented shellac.

Fiberglass resin, I have some of this also.

Are there any other methods that I should try.

I am going to take a piece of MDF from my shop, unheated.
I will also out of the same piece heat some in the oven and keep them inside.

Any other thoughts?
I think with the time and money people are investing in speakers it would be a good idea to try to come up with the best methods possible.
I will start a thread on it when I get started.
Dave

[lunchmoney]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

I think it is controlled test time.
I am going to make up some right angle test pieces and glue them up with Tite Bond II. Then seal them on all sides.
So far I have;
Yellow wood glue, mixed 60/40. Is the 60 water? Does it matter which type.

Shellac, I have the Bin 123 white pigmented shellac.

Fiberglass resin, I have some of this also.

Are there any other methods that I should try.

I am going to take a piece of MDF from my shop, unheated.
I will also out of the same piece heat some in the oven and keep them inside.

Any other thoughts?
I think with the time and money people are investing in speakers it would be a good idea to try to come up with the best methods possible.
I will start a thread on it when I get started.
Dave

"60" is glue

Great idea on this. Make sure you follow up with a report 6 months and a year later.

[donparsons]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

Brian, I have to say that overall the 2:1 mixture of Elmer's wood glue to water was terrible.

Too thick to spread into a nice even coat, and a real pain to sand... lots of hardened "drip" shapes.

I made do though.

I can't imagine how you were able to use undiluted and get a smooth finish

Definitely going back to a 60:40 ratio next time.

As good as your woodworking skills are, why not do 45 degree miter joints and avoid having end grain at all?

[lunchmoney]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

As good as your woodworking skills are, why not do 45 degree miter joints and avoid having end grain at all?

I like roundovers... not much point in miters if you're just going to roundover the edges.

[donparsons]

Re: Anyone ever try Minwax Wood Hardener to seal mdf?

I like roundovers... not much point in miters if you're just going to roundover the edges.

fair enough...

[David Crewe]