You’ve probably come across this large, brown, ugly sheet material at home stores before. But what is MDF?
Does it have any real practical uses in a wood shop or for building furniture?
How do you finish it? How strong is it? What kind of joinery should be used with it?
I’ve been using MDF for various projects in my wood shop for some time now, and I want to help answer these questions for you.
So keep reading to learn what it is, and what it’s not. Learn what kind of projects are perfect for this material, and get tips on how to finish it so it looks great in the end.
Also I’ll cover the pitfalls and drawbacks of using this sheet material.
So let’s get started…
What is MDF wood?
It’s an engineered wood that has grown in popularity due to its low price, high stability, and it being easy to work with.
What does MDF stand for? Medium Density Fiberboard.
In a nutshell, it’s a mixture of sawdust, wax, and glue, which gets heated and compressed into its final thickness.
What’s left is a smooth, flat, heavy engineered wood product that can be considered environmentally friendly due to it being made from recycled wood products (sawdust and chips).
MDF Thickness and Types
MDF ranges from ¼” to 1”, but it may be difficult to find any 1” material in most lumber yards. More commonly, you’ll find ¼”, ½”, and ¾” sheets.
A “full” sheet is similar to a 4’ x 8’ sheet of plywood, except the MDF will come with an extra inch each way, so it’s 49” x 97”.
This is handy because MDF can easily take damage on its edges when handling, shipping, and storing.
It’s brown in color normally, but there are a few other types you’ll come across in home stores or lumber yards, and that is basically variations of being laminated or veneered.
Laminated MDF is covered with a finished material such as melamine, or a wood veneer making it look like plywood.
Another type you’ll find is treated MDF, which will come with a color marking to indicate its treatment – red or blue being fire retardant, and green being moisture-resistant.
What Projects Are A Good Fit For Building With MDF
The surface of MDF is harder than plywood, and takes paint really well. It’s also very easy to work with.
In fact, it can be milled and shaped with the same tools you use for working with wood, but the MDF will come out with crisper, cleaner edges in many cases.
This is because there is no blow out, splintering, or chipping of the edges when cutting or routing MDF.
And because of its incredibly strong and hard surface, MDF is great as the finished, flat surface of many project types, including:
- Table tops
- Cabinet doors
- Drawer faces
- Trim molding
- Decorative panels
It’s also great for casework in general. For the most part, if you can build it with plywood, you can build it with MDF.
And because of its smooth surface and overal stability, it works great for a substrate to be veneered.
But plain, raw MDF is pretty ugly. Not only that, it off-gasses toxins if left unsealed (though the level at which it off-gasses is negligible).
So always plan on sealing/finishing. Painting is the typical finish of choice, as it takes paint really well and becomes completely sealed when complete.
But for simple shop projects like work bench tops and shelving, you can coat it with a couple coats of lacquer or polyurethane.
Drawbacks Of MDF Wood
It’s far from indestructible
While the overall integrity of the board is high, and its flat face is incredibly hard, the corners and edges are susceptible to damage.
If you drop it on it’s corner, you could completely blow out a section, destroying a few inches of material easily.
Also, the edges can likely take damage if screwing or nailing near them, so always pre-drill clearance holes and pilot holes when screwing. And if you’re nailing, I would suggest reinforcing with glue, and using finish nails with a finish nailer instead of a hammer and regular nails.
Does not handle moisture
Don’t let regular, raw MDF get hit with water for any period of time. It will soak in and make it swell up.
This swelling can literally double its thickness, obviously ruining the piece in the process.
A full sheet of ¾” MDF is over 100 pounds. And because the corners are easily damaged, it can be risky to attempt to fumble around carrying such a heavy piece by yourself.
Not only that, coming from a guy who’s had back surgery, I can tell you that handling something this heavy, and this awkward, is a bad idea (unless of course you have a helper).
So the easy fix is to buy half sheets or quarter sheets as needed for your project.
Created with Formaldehyde
Most MDF contains Formaldehyde. But the usage of this substance is heavily regulated by the EPA. The trace amounts used in MDF may not actually be harmful at all.
Nevertheless, you should be aware that it does contain the carcinogen, and the toxins from the formaldehyde will off-gas for a period of time from the raw MDF. Sealing it with paint or a clear coat finish will stop this off-gassing.
Makes a lot of fine dust when cutting
And this is a fine, powdery dust that may fill your shop. So if you’ve got a big MDF project coming up, be sure to get a good respirator dust mask, and do your cutting outside if possible.
Unsupported spans (like shelves) may start sagging
For example, a plain piece of MDF screwed to 2 shelf brackets, will likely start sagging in the middle, depending on the weight of contents, and length of the shelf.
This can be fixed by securing stiffener boards to the front and back edges, vertically oriented. You can round over the front one and make a bullnose with it, which will make the shelf look better anyway.
MDF Project Joinery And Construction Tips
When building shelves, attach stiffener boards or bullnoses to the long edges to add rigidity.
Use MDF for simple, cheap molding and decorative panels. If you don’t want to see exposed edges, trim the MDF with molded strips of solid wood.
If you’re building a project with doors and it will be painted, you can make raised panel doors using MDF as the panel. About half way through this video, I show you exactly how to do that using your table saw.
Like with plywood, building any kind of casework with MDF requires multiple sides of the individual pieces to be joined. This creates a very strong, solid structure.
Joining along the edges can be as simple as using screws. But to really beef up and make these joints stronger, I would suggest using the following joinery techniques:
- Tongue and Dado
William Duckworth did a great article on this topic for Fine Woodworking magazine.
MDF Board Cutting, Drilling, and Finishing Tips
Buy MDF in half sheets (4’ x 4’) or quarter sheets (2’ x 4’) to reduce the weight and make it easier to handle this heavy material.
Wear a respirator mask when cutting and routing MDF, as the dust it creates is very fine.
When working with large sheet material, break it down into more manageable sizes using a circular saw and a straight edge guide, like you would with plywood.
When cutting laminated or veneered MDF, it can help to use a utility blade to score a line along the cut-line just before cutting. This will reduce the chance of chipping the veneer.
Always predrill clearance holes and pilot holes when using screws in MDF. If it leaves a mound around the screw hole, clean that up with a putty knife.
The edges are like a sponge and will take a lot of paint or finish, so seal the edges first with an oil-based filling primer or a drywall sealer, before finishing.
Use an oil-based paint on MDF, and avoid water-based paints. Sand after the first coat and then apply another coat or 2 to create a really smooth finished surface.
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