Painting MDF?

[SonomaProducts.com]

If you have seen any of my posts before, you'll know that I usually think I know it all but apparently I don't and now I have a few questions. My domain consists of solid wood and the ocassional ply for all my finished goods type production. I use MDF all the time for fixtures, etc. but have never incorporated it in a finished piece.

I am building a fireplace surround and mantel for my new home. It seems best to build some of the parts from MDF. It will be painted.

Q's.

1. Is MDF paintable? It ssems the moisture will screw it up. Is there some priming method required?

1. I seem to recall a variant that has a paper coating. Is that required?

2. What about edge prep if you are using the papered version.

1. I will have a scenario where I want to use butt joints. I want to sort of puttey the end grain (or edge) and fill the gap of the butt joint and sand it out smooth so it won't show once painted. Could I just use like sheet rock taping compound or is there something better?

BW

[Gus]

Yes, mdf takes paint very well - at least on what I will call the "face grain".

On the "edge grain", yes, you should prime it. ordinary joint compound and a light sanding works well.

You're thinking of "MDO". MDO is NOT the same as MDF. MDF is "Medium Density Fiberboard". MDO is "Medium Density Overlay".

Originally developed for sign painting and concrete formwork industries, MDO is also used for other applications as a paintable surface.

It is a plywood product, with a paper face overlaid on the plywood substrate with an exterior grade (usually) phenolic adhesive. MDO is designed to have a smooth paint receptive surface. One or both faces can be faced with paper, and is found in 4' x 8' sheets from 3/8" to over an inch in thickness. MDO is used for short term signs. MDO is not recommended for permanent sign faces because it is susceptible to Warping, Water log, Mold Etc.

MDO can be edge-banded or filled. It is plywood.

However you join MDF, take care with the fasteners. Use "Spax" screws or the like. You need a coarse thread with MDF.

Also, be aware that MDF likes to "mushroom", so use of countersinks on BOTH sides is recommended.

[Leon]

I have a customer that moves every 5 years or so and insists on redoing the kitchen each time. He is sold on MDF flat panel doors, which I cut out and drill for Euro hinges, he spray paints the panels in his garage. He typically lives in $500,000 homes so I don't get the attraction to this type of door but it has the look that he is going after. That said, these MDF doors are the only thing he spray paints and I'll have to say that his results are pretty darn good. He does use an oil based primer and paint and lightly sands the primed surface before applying the final paint coats. No sanding of edges before the primer goes on.

[SteveBell]

I apply Kilz or Zinsser primer and then sand it smooth.

Work wallboard compound or wood filler into the edges. They'll soak up lots of paint if you don't. It's best if you don't have exposed MDF edges. I would put edge trim there.

Use biscuits, splines, or backers to keep the surfaces aligned. Fill the crack with wood filler and sand it smooth, then do the prime and paint.

[Greg O]

I used sanding sealer the other day to seal up MDF. It seemed to work well. Greg

[Robatoy]

What we have done, with good success, is to fill the edges of MDF and plywood, which are very absorbent, with lacquer-based automotive putty. One brand we use is called Green Stuff. It is the last filler/ putty automotive guys use before they spray on the primer. It dries quickly and sands beautifully.

[Ed Pawlowski]

Yes, but why would you want to? At worst, three coats of clear poly. Best would be a shellac and French polish. If you are going to take the time to make a nice project, don't cover up and hide the material. I use 8d common nails too and the contrast with the heads is a beauty to behold.

Given your sense of aesthetics, I don't think we will ever see you doing one of the Designer shows on cable TV.

[-MIKE-]

I've used KILZ on a whole sheet before cutting. Rolled on one coat and a light sanding-- it looked like melamine.

[SonomaProducts.com]

Not sure I follow. Was this some kind of jab at my work?

[Charlie Groh]

...maybe, maybe not...heh...OTOH, I've built a rather large hearth out of MDF, with wood plant-on trim, mitered the corners and filled where appropriate with Bondo...used poplar for the mantle and hired a boat painter to apply a two-part varnish. Been 10 years and still standing tall...MDF paints up great!

cg

[Ed Pawlowski]

Surely you must have some sense of humor. Have a coffee and re-read. You may also want to dig up some old posts about finishing cherry.

[SonomaProducts.com]

I thought the only appropriate finish for Cherry was semi gloss latex paint. Maybe I'm confused.

I am cover> Surely you must have some sense of humor. =A0Have a coffee and re-read. = =A0You

[nailshooter41]

Now that's interesting. I have been using Durham's Rockhard for years on that stuff. It dries fast, sands very well, but on occasion there is an adhesion problem with small fills (like large nail holes) in materials like MDF that tend to be hard and dusty.

Any adhesion problems? How fast does say, and 1/8" diameter take to dry before sanding?

Can you put latex coatings on it as well as solvent based?

Have a manufacturer handy?

I am seeing and using more and more of this stuff in different grades, and frankly, as poor as the wood is that I have been purchasing for some time I am getting to the point I prefer it. I prefer the end product, but don't prefer working with it.

Man, I miss wood. If you had asked me 30 years ago if I thought we would be using modified cardboard for baseboards, finger jointed nastiness from Chile for trims, sheets of termite leavings instead of doug fir (which I thought was crap at the time) I never, ever would have believed it.

Robert

[nailshooter41]

would look great. Did you do the design work as well?

Robert

[Ed Pawlowski]

I +++++++++++++++++++++++++++++

Exactly. The opposite is MDF finished with the grain showing.

[Ed Pawlowski]

I am covering an existing brick fireplace and mantle so I am a bit constrained. I also have a home that is not so upscale so I want to bring in some class but not so high end that it is over done. I am using some classic influences and holding the stacked molding down to a minimum. I am using an MDF backfield to be CNC'd by my buddy to match the shape of an archway I am constructing betewwn the living room and kitchen to tie the things together. Here is a link to my current design.

design. That should be quite a bit of upscale.

[SteveBell]

I haven't tried it, but some people recommend using wood glue to seal the edges of MDF. Shellac should work fine, too. You're just trying to prevent that area from soaking up tons of paint and leaving a rough finish.

Pre-drill before you put in screws. MDF is so dense that it swells a little wherever you use a screw, especially if you screw into the edge. Someone else recommended countersinking both sides of screw holes, and I agree.

[Robatoy]

The stuff we buy, is green..and called Green Stuff... I keed you not. I also seen this around the shop, I think it is the same kind.

'll look on the toob when I see it.

[SonomaProducts.com]

[nailshooter41]

url.com/8yjl2l

I would never have thought about using that stuff on wood. I would love to find a super fast dry filler. That stuff doesn't look like it would be good for trim nail holes, though.

I am looking forward to seeing what you actually have. I to have some trick stuff to make my work easier and faster in the toolbox.

Robert