DD2 added crown to the areas w/o it when she bought a new home several years ago. Added wood to the master bath and hasn't had any issues.

Here is a thread I just started today about her bath:

Here is a link that might be useful: My thread

We have wood molding around the doorframe, directly next to plastic crown molding on our built-in medicine cabinet… you can’t tell the difference.

It just so happened that the crown molding I liked was plastic… they look the same once painted.

Here is a link that might be useful: Photo of cabinet molding.

I'd recommend either wood or foam/plastic.

I've seen the seams of FJ crown telegraph through paint over time. MDF could be okay with primer and paint. But if there are any non-factory, site milled (routed profile for example) MDF profiles that are primed and painted over, the MDF can absorb moisture over time and the milled edges can develop a sandpaper-like rough texture.

So for a humid environment, I'd recommend a urethane foam crown (or "plastic") or a primed (back primed too) and painted non-FJ wood.

If only factory edges will be showing, MDF could perform well, but it's a little more of a gamble over the long-term.

Thank you very much for sharing your good experience, Allison. Your DD2's bathroom is so gorgeous and totally different from the original. I love it!

For the wood crown molding, was it done with coped corner joints or mitered corner joints? Is the size about 3.5"? Yesterday, I talked to the general contractor and he said he would not do coped corner joints since it's much more difficult than the mitered ones and takes much more time to do it. But wood crown moldings tend to open up at the corners due to humidity and temperature change. I also need to have crown molding installed in living room and family room, and probably kitchen. How it will be done properly to minimize the chance of future opening up is a concern.

VictoriaElizabeth, thank you so much for sharing your experience with plastic crown molding, which is very helpful. Your bathroom is so beautiful.

Thank you so much, Mongoct. I would look for urethane foam crown ( or plastic) at HD, Lowes, and moulding shops. Does it look the same as the wood for crown moulding?

The chaleston 4 1/4" crown moudling which I planned for family room and living room only comes with MDF and FJP. I don't know if colonial one (3.5", planned for bathrooms) comes with wood. I'll check that.

Thank you very much for your detailed response to my concern of FJP crown open up at the corners due to seasonal humidity change (posted in remodeling forum). You suggested coped corners versus mitered corner joints and scarfed and glued running joints with backing versus simple butt joints. I don't quite understand the backing part. I'll figure that out. Yesterday, I talked to my contractor (my remodeling will start next Mon.). He said he would not do coped corner joints, since it's much more time consuming. One day's job would end up 3-4 days. Is he right?
Besides bathrooms, I also need to have living room, family room, and possibly kitchen installed crown moulding. So proper installation to minimize future opening up at the corner joints is a main concern. He told me he would charge me for repairing the possible opening up if I use wood instead of MDF.

Really appreciate your professional help.

It's not necessarily that the mitered joints of the FJ molding will open up more than non-FJ molding. Mitered joints for FJ and non-FJ will act the same for same-species woods. It's that the actual finger joints themselves can swell a bit, causing some or all of the glue lines to telegraph through the paint. You can end up with little vertical lines every 12-18" or so along the run of molding.

FJ molding has gotten better over the years. But the humidity swings in a bathroom could certainly challenge any FJ trim.

Coping really isn't time consuming. I have to preface that I never use caulk on any molding. My mitered joints are tight, no caulk needed. When attacking an inside corner, coping is actually faster than mitering, especially if the joint is not a perfect 90-degrees. Coped corners will not open up with seasonal movement like a mitered joint will.

So the sort of funny thing is that coping can be faster, and more durable.

I will say some folk are intimidated by coping. MDF can be coped too, but the pointy end can be fragile. But it's ridiculously easy and coping can eliminate a lot of joint problems caused by wood movement and mitered corners.

Mitered corners? I think mitered MDF can give a more stable inside corner joint than mitered softwood. Softwood (most any wood) has unequal rates of movement along it's length versus its width. When lumber shrinks more across its width than length, that's when mitered joints can open up, the "V" gap is very typical. MDF has a lesser rate of movement than wood like pine, plus it moves equally in both dimensions. So an MDF joint could open up, but it's less likely to do so, because it moves less to begin with, plus because its equal movement in both dimensions puts less stress on the joint than the unequal movement in a species wood.

I hope that makes sense.

If your guy uses MDF, then that's fine. You can get tight joints with MDF and with glue, they can be durable. An advantage of MDF is that it is a uniform material, there is no unequal expansion on one dimension when compared to another. So miters are not stresses as much with MDF as they might be with a true wood like pine.

FWIW, when mitering inside corners for crown, I cut the piece of crown slightly long. Maybe 1/8" +/-, depending on the length of the stick. Then I bow the middle part out away from the wall to get the two ends in place. With the corners set, I then "snap" it in place by pushing the bowed middle against the wall.

That compresses the mitered corner joints, making them less likely to open.

The not understanding of "the backing part", it's fairly simple. I've already written a thousand words, so hopefully these photos will allow for brevity:

A glued butt joint on a 1" by 4" piece of crown will have a glued surface of maybe a little over 1 square inch. And that glued surface will be end grain, which is a weak glue joint. Now add a glued backing block behind that same butt joint. If the block is 2-1/2" by 6", it adds another 15 square inches of glued area to the joint. Much stronger.

Here's a backer block on the back side of a couple of pieces of crown simply butted together:

What the side view would look like:

And another:

Mongoct, thank you so much for your detailed response, very helpful. Sorry for my late reply. I have been busy with other remodeling materials.

I'd like to use charleston FJP 4.5" crown molding for living room and family room because the MDF charleston's profile is smoothed out, much less sharper than the FJP one.

My contractor said coped corner was very difficult to do and much time consuming. He only does mitered corners. Yesterday, I went to the local crown molding shop. They told me they only do mitered corner since coping is difficult to do. Home Depot people also said that mitered corners would be fine with pine, and coping is very difficult to do and may leave some gaps if not being skillful. They all said in case of opening, just caulk to close the opening.

Wow! it's difficult to get a skillful contractor who could do coped inner corners. Are you living in the SF bay area? Can I just go ahead and have the 4.5" FJP charleston crown molding with mitered corners in living room and family room and have 3.5" plastic colonial molding in bathrooms, or switch to Colonial 4.5" MDF molding which looks simpler and more common than charleston molding? My contractor said he would charge me on hourly basis to caulk the corners if they open in the future.

Really appreciate your professional help.

The "ct" in my name is for Connecticut. Though I was in southern CA this morning. So close, but so far away...

Yes, you can change moldings from one style to another within the house, it's done all the time. Your contractor should guarantee his work for at least one year. If the joints open up, he caulks them for free.

Of course, if he'd learn to cope...he'd never have to caulk!

Thank you very much, Mongoct. My contractor said if MDF crown molding opens up, he would come back and caulk them for free. But if I use wood crown molding, he would charge me for caulking the opening every time I ask him back.

In that case, is it better to switch to MDF materials, although the MDF colonial one is so common and MDF charleston's edge is much smoother than its corresponding FJP? Or is it fine to use the FJP 4.5" charleston? Would caulking the corners in case they open in the future be difficult? The ceiling is only 8' tall.

Really appreciate your help.

I think it's a question that you have to work through on your own, you need to sort of figure out what is your biggest concern.

Based on what you've written about your contractor, he seems to think that the corners of his wood crown will open up. He fails to recognize that it is, in part, due to his methods of work. I'll add a caveat that if he is a sloppy contractor, then it's possible his MDF corners could open up too. They really shouldn't. But if he's a "slam bam" installer, who knows?

You are concerned with the sharpness of the MDF profile. I will say that once painted up, and after the novelty of staring at your beautiful crown for hours on end each day wears off, you probably won't notice if your crown has super-crisp edges or slightly soft edges. You'll simply notice the crown. But that's up to you. Would the softer profile of MDF bother you in the future? Only you can answer that.

A slight warning: Paint prefers a slightly soft corner so its film coating can adhere or wrap around the corner. So if your wood crown has super-sharp edges, the painters will usually sand the sharp edges down a tad, what's called "breaking" or "easing" the edge, so the paint can better adhere.

As to your other question about caulking the corners, it's not difficult to caulk. The wood will typically shrink in the drier season, typically in winter. So if your miters opened up, you'd want to caulk them then. In the summer the miters will close. The caulk should flex with future movement.

Don't forget that if they caulk later, they'll typically have to paint the caulk too. Obviously the need for painting could depend on the paint color of the crown.

So it's a balancing act. You need to weigh one concern; a sharp molding profile, against another; the possibility of opened miters and having to caulk those miters. There are pros and cons to each side.

The wild card is your contractor.

Thank you so much for your help, mongoct.

I think I will go with the FJP chaleston one because it really looks better than the MDF one, and my living room and family room have good lighting.

If I could find a contractor who could do coped inside corner, I would let him do it. If I could not, I would have the current contractor do it. I called four moulding companies in the bay area, and they all only do mitered corners.

If it's not difficult to caulk in case the corners open up in the future, I'll do the caulking and painting myself.