sealing MDF edges?

[Matt Ralston]

After seeing some of the work here out of MDF, I'm thinking of trying out making a entryway bench out of the stuff. The bench is for a neighbor, and it basically being done for free, so I'd rather not deal with the extra time to edgeband good ply. The piece will be painted.

So, my questions are:

How do you seal the edges of the MDF so as to have an even coat of paint? Couple of coats of primer? Sanding sealer? Thinned out yellow glue?

Anybody had any experience with the lightweight MDF? Is it the same strength? What about cost?

Anything else I should be thinking about?

Thanks much

Matt in Colorado

[Bob Marino]

After seeing some of the work here out of MDF, I'm thinking of trying out making a entryway bench out of the stuff. The bench is for a neighbor, and it basically being done for free, so I'd rather not deal with the extra time to edgeband good ply. The piece will be painted.

So, my questions are:

How do you seal the edges of the MDF so as to have an even coat of paint? Couple of coats of primer? Sanding sealer? Thinned out yellow glue?

Anybody had any experience with the lightweight MDF? Is it the same strength? What about cost?

Anything else I should be thinking about?

Thanks much

Matt in Colorado

Hi Matt,

Bench out of MDF?? I think almost anything else but MDF.

Bob

[Phil Phelps]

....rather than tell you not to use MDF, ahmmm, I'll tell you how to seal the edges. I've painted more MDF edges than a normal human should. If I can wait a while, pigmented shellac is my first choice. I use a stiff brush, it's called a Fitch brush (found at the sign supply) for the application. You must work it in. It dries fairly fast cause it's alcohol base. But fast may be a couple of hours. I then sand with 150 and recoat. Wait a day till it cures and sand with 220 and paint. This method gives a hard finish. Pigmented shellac dries hard and sands to powder. If your in a hurry, you can use latex flat. Sand between coats and then prime and paint. You can make the edge as smooth as anything you paint. Now about the face. I use joint cement to "fill" the MDF. Trowel it smooth and sand. Prime and paint. The building of a project with MDF is easy. Finishing will take the most time. Be prepared.

[Howard Rosenberg]

The short answer is: none of them.

With all the furniture I've made out of MDF and all the techniques I've used on the edges, the VERY BEST, most practical is: sand the heck out it.
An ROS is best; handsanding is next if you've got a profile like an ogee you need to maintain.
Careful use of 120-grit and you'll be fine.
After you finish the sanding, use your vaccuum or better yet, blow the edges out with a compressor.

BUT:

This is an entryway bench?
How are you planning on constructing it?
(that isn't a rhetorical or antagonistic question - I'm truly interested)

MDF doesn't have any grain and can't support its own weight.
To give you an idea of how I engineer my MDF furniture, shelves are always housed in dadoes & grooves with a face-frame at the front.
Tops always rest on the back, gables and top of the face-frame. This forms a "skirt" to hold things up as time goes by.

The living room cabinets I posted last week have tops that are only +/- 22" deep. Mid-way front-to-back I put in vertically-positioned 3/4" x 2" MDF supports under the tops to prevent front-to-back sagging.

As a side-note, I only use glue - no nails or screws and everything ALWAYS stays together perfectly.

Matt, I'd be very interested in hearing more about your bench. If there's anything I can help you with, I'd be very happy to do so. Use my e-mail howr@interlog.com.

All the best. Howard Rosenberg

P.S. - 3/4" MDF weighs 3 pounds a square foot. What thickness(es) were you planning on using?

[Todd Burch]

Hi Matt.

See this post:
http://www.sawmillcreek.org/showthread.php?threadid=4276

and this post:
http://www.sawmillcreek.org/showthread.php?threadid=3758

While I don't personally have any experience with lightweight MDF, I have priced it and it is more expensive.

Todd.

[Steve Jenkins]

To seal the edges of mdf I mix regular pva glue with water about 1-1 and brush on 2-3 coats letting it dry a bit in between. After it dries completely I sand. I've found that by doing this it reduces the amount of sanding I have to do and also reduces the amount of sealer I need to put on the edges. Steve

[John Wadsworth]

In the past, I've heard Bondo (the stuff auto body guys use to fill dents) recommended for filling plywood and MDF edges before painting, but have never tried it myself.

Anyone on the Creek have experience with the stuff?

[Todd Burch]

John, I've used plastic auto body filler a lot, back in my previous life working on cars. I've also used it to fill holes and voids in wood.

However, as thick as plastic auto body filler is, it could not be used to "seal" edges. It would not soak into MDF - just cling to the edge. However, it could be used to "build" edges though. I would not hesitate to route cured "bondo". Todd.

[Matt Ralston]

Thanks for all the advice guys. Person I'm building this for would be doing the finishing, which probably means that it would not be done as well as it should. hmmm, decisions decisions...

Howard - a little more info. This is a simple bench that the neighbor saw in a Pottery Barn catalog. A pic from the catalogue is linked below. 49l x 17w x 21h. It will be dado and glue construction. Possibly biscuits for alignment and/or whatever the special screws are (conformat?) to decrease clamp time. This thing is a very simple box with three upright dividers so that no span will be more than 15 inches.



Some said stay away from MDF. I suppose my other option would be ply with sold edging. I could do that I suppose, and still may. $20 bucks a sheet for MDF was pretty appealing though.

Thanks again,

Matt

[Todd Burch]

I would bet money that the majority of that bench from Pottery Barn is MDF. MDF would be fine for that application. I personally would use pine or poplar (poplar would be 1st choice) for the bottom frame/feet assembly.

[Hal Flynt]

Ok I used MDF to make some bench tops. 3 layers thick, 2 supported every 16 inches with 2x4 framing. I drilled 3/4 inch dog holes, shimmed it level and sealed it with about 2# shellac. When the surface get too badly beat up, I fip the bad side down to the bottom and line op the dog holes on the top 2 an redrill the bottom, and go another year or 2. I did not use glue to keep it together, just gravity and 2 alignment holes w/ dowels.

As far as sealing the edges, all I used was 2-3 coats of shellac and left it at that. It doesn't look bad to me.

On another lower assembly bench, I topped a 3/4 in. birch ply top with MDF as a sacrificial top.