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Working with MDF Trim 
Question
Forum Responses
From contributor B: I've installed miles of it. Unfortunately, I've never had any problems with it. Yes, it's not very forgiving. Get it wet, fail to use the right fasteners, fail to care for nail holes properly, etc., and you'll be sorry you used it. But used correctly, it paints out very nicely, I'm sorry to say, and it's inexpensive, which makes it even worse - meaning we'll be seeing more and more of it, which is too bad because I hate the stuff. The dust is terrible, it's not like working with wood (which is fun), some of it is heavy, etc. From contributor C: I agree with Contributor B here. I hate it with a passion and avoid it like the plague. It's heavy, it smells, etc. It is though undeniably inexpensive and it paints very well. I guess on some level you could consider it recycling too. The new waterproof "Extira" product is proof positive that it's here to stay. I don't see it in many of the high-end homes we work in, to me it screams "cheap." But that will likely change too. I'm not resistant to change - I just don't like to try new things. From the original questioner: Thanks for the responses. I have never used as trim but I have just countless countertops. Just in case I am compelled to, what type of fasteners would you use for it when used as trim? From contributor D: I've recently trimmed a few houses with MDF and there certainly are some advantages to it, but I've also gone home those days with blood in my nose. I can't believe that's a good thing. From contributor E: To contributor B: I'm interested in your comment regarding filling of nail holes in MDF. We're currently trimming a place using a 12" base that's made of MDF. Painters are filling holes, but the general contractor has mentioned he's had two cases where nails holes in the MDF trim popped or, perhaps, fell out. He's not sure why. Any enlightenment? From contributor B: To contributor E: I've never had that kind of problem happen. Most problems are caused when the painters treat the MDF as if it's wood - fill it first, sand it, then paint it. Because the skin is denser than the core, nail hole leave little pimples or eruptions on the surface that must be cut off with a sharp knife or chisel, then sanded, then filled, then sanded. Otherwise, all the nail holes will photograph right through the paint, every single one. From contributor F: I make MDF doors and solid wood trim. I wouldn't hesitate to use MDF for a crown molding, but not for a baseboard. Mopping a floor will ruin MDF in a couple of years. When I make a mistake or accidentally gouge a door (it happens) I use bondo to fill the hole and then sand it to match. It hasn't ever failed me. I don't think I'd do a house full of trim this way since you'd have to mix a million little batches of bondo. I've cut hinge slots/holes on the wrong side and used this method to fill the holes. (Of course, I always offer to cut new doors if they don't want bondo.) You can seal MDF by using a mixture of Titebond and water. I have made a couple of exterior carved signs out of Extira. It's great stuff, but you have to use oil based primers (it's waterproof you know). It's also fuzzy as a mule.
From contributor G: I've been using MDF for well over 10 years now. Almost every house we trim, at least 90%, has MDF base, crown, and window casing. We use MDF for skirt boards and risers also. Most mantels and columns are cut from MDF sheet stock. These are not starter homes or tract homes, but high end spec and custom homes from around 3000 sq ft to over 6000 sq ft. Just like any product, there are positives and negatives to using it. It cuts and mills easily, but is hard on tooling. Primed surfaces paint very well, but cut and exposed edges do not paint as well, even after sealing with glue or primer. The dust is ferocious, especially when routing. The ultralight mouldings are just that, very light weight. The sheet stock is quite dense and very heavy. None of the MDF has any real structural integrity, but for trim and moldings, it is just fine. MDF has undergone a lot of changes over the last few years. We are probably on 2nd or 3rd generation MDF now so a lot of the bugs have been worked out. Many who used it when it first came out compared it to Masonite, a really awful product, and still refuse to use it. MDF comes in 3 types - Ultralight, Medium density, and High density. Most of the standard profile moldings are made from Ultralight. It is soft, light weight, and very flexible. Nails easily penetrate it and usually don't pucker the material. Sharp edges can chip fairly easily if not handled carefully, but are fairly stable once nailed/glued in place. This is also the type that tends to swell the most when continuously exposed to water. Medium density comes in sheet stock and nominal 1x stock. We use this for stair risers/skirts, mantels, and non load bearing columns. This type is much more stable and does not expand/contract as much as wood does. But, because of the density, the material tends to pucker when nailed. Some distributors purchase sheets in 16ft lengths from the manufacturer and re-mill it into moldings with their own profiles. But because of the many nails needed for nailing base and casing, the puckering problem becomes an issue and people refuse to use it and think all MDF is this way. High density MDF is used for cabinet doors, countertop substrate, and anywhere a durable smooth surface is needed. It is very stable, very dense, and very heavy. This stuff is so dense that if you try nailing it with a nail gun, the nails will sometimes curl up and not penetrate. And if the nail does penetrate, you will most assuredly get puckering. Bottom line - MDF has earned its place in the building industry and is definitely is here to stay. After working with it for awhile, you learn what it can and can't do as well as how to work with it. I have become accustomed to working with it and actually prefer it over wood for most applications. But it is not the be all, end all product. Something else will come along in the future and we will be saying, remember when we used to have real MDF to work with? Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Have you reviewed the related Knowledge Base areas below? 
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