What do I need to know about MDF

[Mitch Richardson]

I made a slab door kitchen for a customer and used plywood instead of MDF for the doors. The doors have subsequently warped. I have researched it and found that slab doors need to be made form MDF. However, I have never worked with MDF. What do I need to know about purchasing it? I have tried to research, but have found very little information. Is there higher and lower grades of MDF? If so what grade do I need to purchase?

The job will be done with cherry veneer adhered with hide glue.

Thanks in advance.

Mitch

[scott vroom]

What grade plywood did you use for the doors that warped? Where did you purchase it? Do you know where it was manufactured? You need to make sure that the plywood you use for fine cabinets is constructed of kiln dried layers. A lot of the import plywood is slapped together without regard to the moisture content of the layers, resulting in 4 x 8 potato chips.

[Mitch Richardson]

Unfortunately this is not an issue of lesser quality plywood. The stuff I used was made in Canada and purchased from my local lumber distributor.
I just need some info about MDF.

[glenn bradley]

I have used whatever MDF was available at the lumber yard where I buy my hardwoods and have had no problems with units that set in an uninsulated garage (for years). I did seal the MDF with shellac but, it was not painted. We have some cabinet pros on here and I am hoping they will chime in with some better (and more specific) info for you.

[John Tallyn]

I'm not an expert on MDF, although have used quite a bit of it. Biggest concerns I have with MDF is the formaldehyde glues used in it. Their are 3 grades of this type of product, HDF, (high density), MDF, (medium Density) and LDF, (Low Density) HDF is almost impossible to find, MDF is the most common, LDF is not usually stocked, but can be ordered. MDF is heavy, machines very well, is for the most part stable, but does not have much strength horizontally, for something like shelves. It is not water resistant, in fact water will cause huge problems, any water you get on unfinished MDF will cause swelling, that for the most part is impossible to repair. Be sure to wear dust protection when you mill, sand or saw MDF with power tools, the dust is very fine, and will get everywhere. If you choose to use a water based finish it is imperative that you first use a primer that is oil based, I usually use shellac to cover any MDF prior to painting with any type of finish, I've had very good luck with the shellac sealing the MDF. The edges are very porous, most people will use something like drywall paste to seal the edges before priming or painting. MDF is actually pretty easy to use, other then the weight. There is a company that I believe is locate in Oregon that is manufacturing an MDF that does not use a formaldehyde glue, but I've been unable to get any info on it. You need to make sure you drill holes for any screws you plan on using, other wise MDF will split and crack. I don't use tapered screws on MDF, just straight screws, with a heavy thread, I believe rockler makes a special screw for MDF, although I've never used them. When you drill, make sure you have a clean backer behind the MDF otherwise it will chip out. MDF does take a finish very well, and requires no sanding, and looks very nice when finished properly. If you have access to old issues of FWW, they have some very informative articles on working with MDF. Not sure this info will help, I'm sure others will be along to provide more info.
Good Luck
John

[David Prince]

I made a slab door kitchen for a customer and used plywood instead of MDF for the doors. The doors have subsequently warped. I have researched it and found that slab doors need to be made from MDF. However, I have never worked with MDF. What do I need to know about purchasing it? I have tried to research, but have found very little information. Is there higher and lower grades of MDF? If so what grade do I need to purchase?Mitch

Slab doors do not need to be made from MDF. Cabinet makers have made plywood slab doors for as long as plywood has been around.

You can make them from MDF. I have found that screws don't hold as strong in MDF when you attach the hinges. MDF is easy enough to router a nice edge. MDF is stable, but heavy. You can buy pre-made Cherry veneer MDF core plywood. It is premium A2 grade and expensive, but will be quality.

[Steve knight]

did you finish both sides of the door? did the door get a lot of humidity or water on one face?
of course there are differences in mdf. The stuff at the borg does not have as hard of a face and it is nto as dense as what I get at my lumber store.

[scott vroom]

I've made a number of MDF raised panel doors (with hardwood rails/stiles). MDF will warp if primed with a waterbourne finish. As one poster suggested, prime with an oil based product.

I just re-read your original post. You mentioned you made slab doors from plywood. Did you edgeband? Just curious.

[Leo Graywacz]

You can get Cherry veneered MDF and apply an edge tape made from Cherry. If you are using but hinges that will be mortised in then MDF is probably a bad choice to do this route. If you use Euro hinges it will work fine.

You can also use a MDF core with a solid wood edge (1/2" wide) and then veneer over the slab. Make sure both sides are done the same to equalize the panel. This will give you a nice solid wood edge that will hold screws very well.

[Jim Foster]

I've seen low cost plywood slab doors that were twenty years old or so that were not warped at all, and I've seen relatively new ones made from high grade furniture plywood that warped very soon after being made. The only difference I can think of is the low grade ones were painted with an oil base paint. It would be nice to know why yours warped. (It could be that both sides of the door need to be finished simultaneously so one side does not suck moisture while waiting for sealing) Years ago, I machined a bunch of MDF into simple window and door casings and base trim for my house. It was like cutting butter on my table saw and it takes a beating after being installed.

[Andrew Pitonyak]

I drilled then threaded a hole (I have a tap and die set) in MDF. Next, I dribbled in some CA glue, which hardened the threads. Finally, I ran the tap into the threads again. This seemed to hold machine screws very well.

Cutting MDF generated a significant amount of dust. perhaps I should have said a disturbing amount of dust when I cut some with a circular saw and then I used a router.

[Chris Tsutsui]

I love MDF and just buy "A" grade MDF found at big box stores. California has more restrictions on MDF being certified so maybe it's better, I don't know...

I made a bathroom medicine cabinet out of MDF and all my trim moulding is MDF in the bathroom. I used an oil based primer and paint and the medicine cabinet has a slab door that's inset. It hasn't moved at all in over 3 years.

My router table top is 1.5" MDF treated with several coats of BLO and wax, it too is flat as can be.

One thing to watch out for is Hide glue has water in it and water is the enemy to MDF. Think of MDF as a solid piece of cardboard and it will swell up if you use too much glue. Also if you sand the external hard hard layer of MDF off, then it can get "fuzzy" or lose its glass smooth texture unless you use a fine grit. MDF machines extremely well with sharp tools and will create some pretty fine dust. It is afterall, mostly resin/glue and sawdust.

[Rob Cunningham]

Here's a little bit of info I found when researching for a project that a customer told me they wanted made from MDF. Their friend told them it was the best thing to use. After reading this, they decided against using MDF.

"When MDF is cut, a large quantity of dust particles is released into the air. It is important that a respirator be worn and the wood be cut in a controlled and ventilated environment. It is a good practice to seal the exposed edges to limit the emissions from the binders contained in this material.
Formaldehyde resins are commonly used to bind MDF together, and testing has consistently revealed that MDF products emit urea formaldehyde and other volatile organic compounds that pose health risks at sufficient concentrations, for at least several months after manufacture.[4][5][6][7][8] Urea formaldehyde is always being slowly released from the surface of MDF. When painting it is good idea to coat the whole of the product in order to seal in the urea formaldehyde. Wax and oil finishes may be used as finishes but they are less effective at sealing in the urea formaldehyde.[9]
Whether these chronic emissions of formaldehyde reach harmful levels in real-world environments is not yet fully determined. The primary concern is for the industries using formaldehyde. As far back as 1987 the U.S. EPA classified it as a "probable human carcinogen" and after more studies the WHO International Agency for Research on Cancer (IARC), in 1995, also classified it as a "probable human carcinogen". Further information and evaluation of all known data led the IARC to reclassify formaldehyde as a "known human carcinogen"[10] associated with nasal sinus cancer and nasopharyngeal cancer, and possibly with leukemia in June 2004"

[David Thompson 27577]

What do you need to know about MDF?


It's mush. It's wood flour and some sort of binder (usually toxic, at least somewhat). Cutting the stuff yields a huge cloud that will choke you, unless you have the best dust collection and the best dust protection (BOTH).

In addition, IMO, it does not take profiles nearly as well as some might think, painting it with modern coatings (water based) causes it to swell, usually unevenly.

If it gets wet prior to finishing, it's junk. Even a small drop of perspiration can ruin a workpiece.

And it's heavy.

And prone to knicks and dings. Which can't be repaired effectively.

Other than that, it's great stuff. I mean, it's flat, and inexpensive, and all.

[Mitch Richardson]

We are a small wood shop that does 97% of our work in solid wood. We have always turned to veneer core plywood or baltic birch when we needed something dimensionally stable. Unfortunately this kitchen project has shown me differently. Plywood does warp (even really good stuff). We did not make any errors in the prep or finish of the plywood. There are something like 56 doors and drawers in this kitchen and all but 5 are plywood. Of those 6 have warped. I used two lot numbers and all of the warped doors are from the same lot. That says to me that the warping issue could be related to the particular lot. I have researched the issue and have found that cabinetmakers who do solely kitchens for a living are aware of this issue and as such avoid the use of plywood for slab door construction.

I purchased uniboard mdf for the door replacements. They seem to be reputable. I am just trying to make sure I do not get any further phone calls.

Thank you all.