MDF as Interior Trim

      Does MDF make good trim, especially in a humid climate? Pros share their observations. December 20, 2005

I'm building an ocean front home and want to use MDF moldings because of its following characteristics: 1. More stability than standard pine moldings. 2. Harder, more durable material to withstand heavy treatment - this home will get heavy use during the summer months 3. A more durable, painted finish.

While the home will be air conditioned, how concerned do I need to be with humidity before, during and after installation? Once the home is painted and the air conditioning is running, I'm assuming I'm out of the woods? Also, is there any reason to seek out the more expensive moisture resistant MDF versus the normal, high quality MDF moldings?

Forum Responses
(Architectural Woodworking Forum)
From contributor A:
I have been using MDF moldings on the beach here in SE Florida for some time with very good results and no problems, especially when the MDF is painted. One precaution that I would pass on to you is to make sure that you use a good quality sealer on all surfaces. That includes all cuts to the moldings. Also, use only the highest quality adhesives and caulks. I learned a long time ago that when you are building a house in the tropics, you treat its construction as if you were building a boat.

From contributor B:
I've found MDF superior for crown, most base, chair rail backers, shadow and bed moldings, some window trim, and casing backers. It handles well, copes evenly, and paints up beautifully. It nicks and dings easily, so I donít like it for door casings, chair rails etc. I also donít recommend MDF base in bathrooms, laundry rooms and other places that might get wet. I do wonder what the life of MDF is predicted to be, compared to pine or poplar.

From contributor C:
I'm surprised by your durability comments regarding use of MDF on casings and chair rails. The manufacturers market their product as being harder and more ding resistant than pine. What gives? Are you specifically referring the vulnerability of square edge S4S type casing? I could definitely see the square edges as a potential weakness. Your elaboration is much appreciated.

From the original questioner:
To contributor A: Can you comment on what glues, adhesives and caulks that you're happy with? Also, how meticulous are you about the exposed cut ends of the MDF during installation? Do you have the trim carpenter seal these as you go, or is having the painters follow the trim carpenter quickly the key?

Lastly, when you refer to sealers, I'm assuming you mean primers like Zinsser? If so, what brand are you using?

From contributor D:
MDF is not as tough as pine. It is a good way to save money on painted trim that will be installed in areas that are not prone to dings. I agree that it is not the best choice for casings or chair rail. I even have my doubts about outside corners of base board that are going to get banged. However, if you keep some of the primer and paint, a little Bondo and a touch of paint will make it good as new. Are you the contractor or the homeowner?

From the original questioner:
To contributor D: I'm an owner/builder on this job and a former custom general contractor and home builder here in NC. This is a personal investment property. This is my first project on the coast. In my prior general contractor life, when I wanted to save money I used poplar trim, but it moves a lot. I was hoping MDF would be an inexpensive and better performing alternative to wood trim.

From contributor D:
To the original questioner: I think I wasn't clear. MDF works for trim. And if you do use it where it picks up a ding or two, painted dings are easy to fix. Itís a good way to save money on materials. In my area it gets used more and more these days. Aside from any MDF manufacturing pollution concerns, it is probably a good way to preserve wood resources and therefore good for ecology. I agree that it shouldn't be used where it could be exposed to water.

From the original questioner:
To contributor D: Thanks for clarifying. It does sound though like you have some reservations about the material in high traffic areas as well as the moist bathroom situations?

From contributor D:
Yes, and Iím sorry to seem hesitant. Iíve told you exactly what I tell clients who ask me what is the least expensive painted trim I could install. I tell them MDF works, but it may get dinged if used in certain applications. However, if it gets a chunk broken off, Bondo and paint will fix it to invisibility. It is not appropriate for a bathroom baseboard.

From contributor A:
I am the draftsman, not the installer. My comments about the best caulks are based on information that I get from my installers. My comment about the best adhesives is based on the fact that MDF does not have the ability to handle screws or nails. It may be able to handle drywall screws, but that's about it, so the adhesive is critical. The best product will handle mold, insects, moisture and other deficiencies. The quality of the adhesive is very important with an MDF application. Hardwood also dings, as does plywood.

Yes, you could say I am meticulous. All the cuts that were made to the shutter and casework applications that I posted on the Projects Forum were soaked in Thompsons, as well as all other cuts including over 10,000 square ft. of Cypress that I used on that job on the North Coast of Jamaica. I'm happy to report that all the wood is still where we put it and in great condition even after its initiation by hurricane Ivan in 2004.

From contributor B:
Iíve installed miles of trim using dozens of species, and various wood products. Each product has its place, and each guy has his preference. As I said, in some situations (crown especially), I believe MDF is superior to pine or poplar. In addition to that, itís cheaper. However, the sales guy is feeding you a line when he says that MDF is harder than pine. True, it may have a higher density than some woods, and may certainly have a higher surface strength, and may be less prone to some kinds of dings, but it is sometimes more prone to dings, and more difficult to repair. For instance, if you were to dent that pine sill you just installed, youíd find a rag, dip it in water, pool a bit on the dent and voila Ė dent gone. Try that with MDF. Trims with more delicate edges Ė beaded casings, for instance, are not appropriate for MDF. The little beads break or chip, and donít glue on quite as nicely as real wood. As far as S4S goes, I would actually think that might be an acceptable application for MDF, but I donít like it. I agree with contributor D that base outside corners can be a problem in some instances.

From contributor F:
MDF is ok for countertops, but I wouldn't use it for molding. It paints nice, but that's about it. I have seen damage caused by steam-cleaning the carpet. I think wood is the best choice for molding. I feel the molding should last the lifetime of the home, and not only the time that the contractor guarantees.

From contributor A:
I'm not really a big fan of MDF but for tops or painted surfaces it does give a really flat, smooth and consistent surface as long as it is sealed well. Also, the lightweight Trupan is better and lighter - the only problem that I really have is that the product physically stinks. The odor is offensive and I will not allow it to be kept in my office. I have been told that if MDF is not sealed on all surfaces, it will leach toxic fumes. I'm not sure if that is true but I really don't need that.

From contributor G:
If this is more of a cost issue then you will likely want to go with MDF. However, if stability and hardness are the issues then I would go with a hardwood molding. If the wood is properly dried, properly relieved and machined, it can be left to acclimate in the room where it is being installed for about 10 days. MDF is great for certain applications but it is not a cure all or a perfect product. I have seen damage to MDF from steam cleaners, etc. Also, if you have an ocean front home, a hardwood molding will be classier and will add more value to the home.

From contributor F:
MDF is a great product. It makes a usable product out of unusable stuff. We do need to conserve, and minimize our waste. However, it should be used wisely. Using MDF for molding is not a wise choice, especially not for a base molding.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor J:
Having worked in the industry for the last 10-12 years Iíve observed that domestically produced light weight MDF absorbs half the amount of water that a typical imported Ultra Light product does. Also some of the domestic manufacturers are working with water resistant and fungus resistant substrates. I have had MDF in both bathrooms with a tile floor and Iím going on 5 years and have had no problems.

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