Best methods for finishing MDF

[LouC]

Re: Best methods for finishing MDF

I've seen bu*t joints on MDF show up two years after they were perfectly finished by a master craftsman (not me!) who refinished pianos for a living. (I watched Herb turn cheap cherry veneer patches into extinct 1870's era rosewood with brushes, dyes & stains. That 2 year restoration went for $300,000)
Unless you live somewhere with constant heat and humidity levels, joints lines are probably inevitable. Better quality MDF has a hardened outer layer and softer core material so exposing the edge is an almost impossible battle. It's why I quit trying to paint and went to veneer and/or Duratex.

His recommended solutions to me:

• veneer over the face with joints with a tight grain wood (maple,yellow pine,...) then fill the pores and prep the veneer for paint.
• Change your colors at a joint
• Miter or bevel instead of roundover
• Make the joints a feature with a groove painted in contrasting color
• Use a flexible clear finish that dissolves prior coats & crosslinks --in case you want to refinish down the road (lacquer, acrylic, not polyurethane)

[Jim Holtz]

Re: Best methods for finishing MDF

I've tried a number of different methods of sealing the seams and the only one I've found that is permanent is 1/8" MDF. I cap the ends/surfaces with all of the seams using 1/8" MDF and then you just have a 1/8" seam that is on an edge to worry about.

BTW, bondo is the best solution other than 1/8" MDF I've found for seams.

Jim

[kirk78h]

Re: Best methods for finishing MDF

If I was covering a seam that I never wanted to show, I would use a Dynatron bumper repair kit. I've used this for several custom automotive interior fabrications, and I've never seen it crack. Other interior mods I've seen that used bondo almost always fail because it sets up too hard; and has no 'give'. Dynatron remains flexible enough to withstand some expansion. I've never used it on MDF, so I don't know if it would have proper adhesion directly. I have seen other people start with MDF mounting rings, then add epoxy putty for molding / large gaps; then finish with Dynatron. Just my $.02.

Kirk

[djg]

Re: Best methods for finishing MDF

If you are really energetic, you might try a layer of light fiberglass cloth with epoxy resin. Homebuilt aircraft use this over foam cores, model aircraft use it over veneer covered foam wing cores, and stitch and glue homebuilt boats use it over plywood.

[davepellegrene]

Re: Best methods for finishing MDF

If I was covering a seam that I never wanted to show, I would use a Dynatron bumper repair kit. I've used this for several custom automotive interior fabrications, and I've never seen it crack. Other interior mods I've seen that used bondo almost always fail because it sets up too hard; and has no 'give'. Dynatron remains flexible enough to withstand some expansion. I've never used it on MDF, so I don't know if it would have proper adhesion directly. I have seen other people start with MDF mounting rings, then add epoxy putty for molding / large gaps; then finish with Dynatron. Just my $.02.

Kirk

Would this be the same stuff you spray on a rubber bumper before you paint? I have some of that I sprayed on some vinyl siding to change the color. Then sprayed acrylic enamel over it. It all stuck really well.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

If you are really energetic, you might try a layer of light fiberglass cloth with epoxy resin. Homebuilt aircraft use this over foam cores, model aircraft use it over veneer covered foam wing cores, and stitch and glue homebuilt boats use it over plywood.

I have used this method a lot. To much because now I have become sensitized to epoxy. I am sure this would work, but not practical for the average person to use.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

Thanks so much for doing this!

I would add shellac into the mix. Although I tried it and didn't like it ("pilled up" upon sanding), many swear by it.

Another I've been curious about is straight elmer's white glue... I think this is Wolf's favorite... although I suspect it would be too thick to get a nice even coat.

Variables that are going to make your evaluation tricky (among many others)... not trying to discourage you, but I'm wondering how you'll factor them into your results:

1. Number of coats
2. How long you wait after sealing, before sanding
3. Humidity

DO NOT do what I just tried, which is a 2:1 mix of Elmer's wood glue and water... too thick to spread smoothly, resulted in some hardened "drip" shapes... sanding was a bitch, but I think I'll be ok... hopefully the 5 thick coats of high build primer will compensate :(

I do plan doing two samples of each. One baked the other not. I will also use Wolfs hand rubbed method. As far as coats I plan on trying to get a build up of all the products so they bridge the seam. I will keep track of how much work and level of difficulty each method is.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

There's a thread somewhere and they swear by some water based filler primer. I think it's meant for MDF and sold for the speaker industry. I know it's white and can't remember what the stuff what was, but it didn't look like mass-marketed junk you usually end up buying at the store. Someone in this forum knows of the stuff of which I speak. Where are they?

FSC88 is a water based filler primer. under $30 a gallon. Can be used on wood also. Wonder if it is the stuff.

[kirk78h]

Re: Best methods for finishing MDF

Would this be the same stuff you spray on a rubber bumper before you paint? I have some of that I sprayed on some vinyl siding to change the color. Then sprayed acrylic enamel over it. It all stuck really well.
Dave

No, this is a two-part mixture that is spread like other body fillers.

[tomzarbo]

Re: Best methods for finishing MDF

Didn't someone... Aaron Hero, I think..... make up some kind of heated rig to cure the MDF in cabinet form before paint? I think it was some kind of high wattage Halogen bulb with a fan type of setup. I think it worked well for his stuff, and his cabinets always had all types of angles and curves, lots of MDF seams to show... and most of his cabinets were painted if I recall...

TomZ

[terryo]

Re: Best methods for finishing MDF

Didn't someone... Aaron Hero, I think..... make up some kind of heated rig to cure the MDF in cabinet form before paint? I think it was some kind of high wattage Halogen bulb with a fan type of setup. I think it worked well for his stuff, and his cabinets always had all types of angles and curves, lots of MDF seams to show... and most of his cabinets were painted if I recall...

TomZ

I always thought that was a great idea, but I've never built a similar setup.
FWIW, I think that John Nail's use of all mitered edges is the way to go, the hard surface is all that is exposed and with several coats of oil-based porch and deck enamel a flawless surface is possible. One "trick" that the car audio guys use, but haven't tried myself is to stretch thin spandex over the surface and then wet it out with thin epoxy, followed with a plastic Bondo paddle to remove the excess. Later, a second coat of epoxy to fill the weave is applied and again excess is removed with the Bondo Paddle. The weave must be filled even if additional coats are necessary. Prime with a good high-fill primer, sand and paint away.

However, the finest finish available is my new, proprietary method.
First the surface of the MDF is coated with patches of Bondo using several colors of hardener to create a varigated appearence which is then sanded a bit to level off the high spots to create a skip-trowel surface.

You then follow up by giving several coats of high gloss Urathane. The very essence of DIY elegance with an intricate interplay of light and shadow!

Remember: Nothing, absolutely nothing, in this World, says DIY like Bondo!

Best Regards,
Terry "The Bondo Master" Olson

[dubbreak]

Re: Best methods for finishing MDF

Remember: Nothing, absolutely nothing, in this World, says DIY like Bondo!

Two words:

Duct Tape

regards,

Dub "The Duct Tape Master" Break ;)

(PS: I am a big believer in the powers of bondo. I've used it for many things, many of which probably shouldn't have been "solved" with bondo. If bondo will fill or smooth the issue.. why not?)

[DDF]

Re: Best methods for finishing MDF

I gave up the battle after 8 coats of enamel still showed seams. Now I use a full size front baffle, and mitre the top corners. Not so concerned with the back and bottom.

Other options are veneer or nasty ol truck bed paint.

[lunchmoney]

Re: Best methods for finishing MDF

I think we all need to embrace emerging seams as a hint of the past...

a reminder of the process...

from whence we came...

yeah...

dig it, daddy-o.

[djg]

Re: Best methods for finishing MDF

How about routing along the joint with a shallow 1/16" to 1/8" deep recess and filling with your favorite filler?