Moulding on a Curved Wall

Installing trim work along a curved staricase. February 28, 2004

Does anyone have experience working with a curved wall when installing trim work? The customer has a curved staircase that starts in the foyer and flows up to the second floor. The drywall follows that curve. She wants picture frame or shadow box along with a chair rail against this wall. She has asked two other general contractors to install this, but they both stated they wouldnít touch that with a 10' pole.

I know there is flex molding available for the boxes that is roughly 2.50/lf but not sure if Iíve seen flex chair rail. Second, what happens to the angles once the trim is bent to fit the curve of the wall? Whatís the best way to take an accurate measurement along a curved wall?

Forum Responses
(Cabinet Making and Installation Forum)
From contributor H:
Everything that you want is all custom made. It is all laid up on jigs/forms, then machined. Where are you? This stuff will cost a very pretty penny if they want it made out of wood!

From contributor R:
Is it the inside of the staircase, outside or both? If it's the outside, the radius is typically large enough that poplar or something like that will bend it without too much difficulty.

From contributor P:
In the "Best of Fine Homebuilding - Finish Carpentry", there is an article on using built-up mouldings and layers of plywood to build a frame and raised panel wall on the side of a curved staircase. As part of it, the installer used 3/8" bending ply, 1/4" ply and 1/8" tempered hardboard for the panels. Perhaps it contains some useful information.

From contributor H:
Take some rosin paper and a pair of scissors with you and make a template of the wall. That way you have the size for the shop or whoever you have do the job.

From the original questioner:
The customer is interested in just a chair rail with base cap picture frames underneath installed right against the sheetrock. I donít have any experience installing on a curved wall and I am wondering what will happen to my joints once laid against the curved wall. I would cut and assemble the frames off the wall and then glue and finish nail them once in place. The molding is flexible enough to be shipped in a tight coil, so I figure there is plenty of forgiveness in the material. If the frame corners were glued and pin nailed and then laid on the wall, do you think the joints will open up? Since this will be painted a semi-gloss white, I can caulk any slight gaps but I donít like to rely on that.

From contributor P:
I had a joint on a curved wall that I couldn't get to match well. This was with flexible base. It matched well when I held the pieces straight and put the ends together, but not when both were against the wall. I joined the two ends with cyanoacrylate, then nailed the molding against the wall. It worked great. I use cyanoacrylate because it gave me a strong enough joint and I didn't have to wait for the glue to set.

From contributor H:
You have to know what the radius is so you know the compound angle that you have to use to cut the miters or whatever you use. If you are joining two pieces of base, either with a mitered lap or butt, you still have to use the radius angle to make the joint work.

From the original questioner:
I can see why three other contractors told her that they would not do this job. What is the best way to measure the radius? Where do I plug this into the formula for cutting crown?

As someone mentioned to use cyanoacrylate (super glue) to glue up joints, I would imagine that both opposing corners would "lip up" or lift together and then could be masked with caulk.

From contributor H:
Probably the best way for you to do it (chair rail) would be to use a couple of scraps to dicker back and forth until you find the right angle to use. One way to determine is to take the angle that the treads are cut on which will be the easiest to find. Still, the fastest is to use two pieces of scrap.

I think the two other contractors did not want the job because it was either too small for them or else they felt that the customer may be a little bit too picky. What you are describing is a very simple trimming job.

I just thought of something that is important - dos this chair rail follow the treads up the stairs? If this is so, then you got a real pickle.

From the original questioner:
Yes. This is a curved stair case. Not only will the trim have to flex horizontally, it will have to flex vertically along the same angle as the stringer.

From contributor R:
Unless this radius is extremely tight and you're talking about raised panels, this is a fairly easy job. I think you're worried for naught! Just get it done.

From contributor S:
If it's going to be painted, why not use deep kerfing and compound, or dampen, soak or boil the mouldings to bend them into position for nailing? It's not stained where you'd need special layups or worry about fill blemishes or even stain discoloration. As implied, this might not be all that hard.

From contributor H:
It's not a really hard pickle, if you are using the flexible moulding. Now another question - on whichever side of the stairs the chair rail goes, is there a full wall on it or does it go to a railing?

If it's a full wall, remember to start with a 90 degree angle and finish with a 90 degree angle - that is the only way you will get the chair rail to wrap around the corner of the wall.

The way I read the thread was that you wanted chair rail in the foyer on a radius wall, not climbing the stringer.

From the original questioner:
Sorry for the miscommunication. The chair rail along with the shadow box picture framing underneath (no raised panel), is to be installed on a radius wall and will climb up the line of the stair stringer.

From contributor H:
Sounds like a fun job - it's easy with the flexible moulding, though.

From contributor E:
I've done a good bit of radius work both with wood and the rubber. I recommend you order a bit extra, and use test pieces. It looks and sounds more complicated than it is. Once you get started, it just comes together. The good part is that when she said two contractors turned it down, then it's automatically worth an extra 50%.

From contributor G:
I do quite a bit of very custom curved work. I had a similar situation but with a very tight radius wall. My task was to provide the components for the shadow box that was a very nasty, detailed profile to match the rest of the room.

The flex-mold idea was rejected due to the inconsistencies in the product and the lead carpenter hated the stuff. The stiles are easy, but obviously, the rails are where the curve and twist occur. They are actually a segment of a helix. This was my approach: I made a curved form to duplicate the wall and stair pitch, I milled several lengths of the profile in bass as it is easy to steam bend and holds its shape. I steamed them and made a 3' section of top and bottom rail. When they were stabilized, I primed them and waxed them. Used them to make a urethane mold of each. When the mold was finished (it took three tries) I poured 20 each in hard urethane. Perfect. Next, I used the curved form as my miter jig on a radial arm saw and pre-mitered everything and delivered it to a happy carpenter and home owner. You can get the urethane from Eager Plastics in Chicago.

One note - the freshly poured pieces removed from the mold have to cure attached to the curved form so they do not deform.

Easy, no. Consistent, yes.

From contributor D:
I am doing a lot of work in curved staircases here in Mi and I deal with this kind of problem most of the time. If the job is to be painted, the easiest way to do it is with flex, but it would be very nice if you could make your own chair rail moulding and the rest of the detail, like I do. Get the rough flex and run your own mouldings if you have the machines. If the job has to be stained, then again, you have to glue strips of wood to the radius that you need and run it through the machines; if you only need chair rail and no raised panels are needed, then bend the strips slightly tighter than actual radius, because it is easier to shoot it in place if you force the radius outward then inward.

From contributor B:
This has turned into a really great discussion so I'll add a description of how we'd make this moulding.

We'd resaw 1/8" strips of lumber to 1" wider than the total rise involved in the project. We would then laminate them on a radius form that has perhaps a 1" or 2" tighter radius than the wall surface. This will allow for springback close to the final wall radius.

When the glue has dried we'd take the curved blank and lay a drawing of the rise curve on the inside surface. Then we would bandsaw out the rise curve. This will give you your final curved blank that matches both the plan and elevation view curves.

Finally we'd run it through a special setup we'd put together on a Williams and Hussey moulder. This would create the profile. The blank would have been made about 8" overlong on each end to accommodate for end snipe and miter cuts.

So, if you want the real thing, either make it yourself or have someone make it in wood for you. Flex trim will work, but remember, you get what you pay for (understand that I tend to be biased towards wood).

From contributor N:
I installed a seven-piece radius crown detail. All of the pieces were made of wood. This was a highly detailed crown. I have also used flex moulding and would rather the challenge of real wood any day. This job sounds like a cake walk - don't shy away from it.

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

Comment from contributor M:
When using the flex-molding for wall frames, use it as you would a conventional molding. You will have to make two 18" practice cuts. Assemble by hand on the wall. Mark with a pencil the connecting corners. Because this is a curved wall you will need to "whittle" one piece at a time. This will be time consuming but simple. Repeat for all four corners.

Comment from contributor A:
Another way to handle curved walls is to get a flexible molding. I've got several curved walls in my home and I recently installed floating wood floors. I needed new quarter round molding for the base board. Flex Trim has a wide range of moldings that can be ordered for just about any curve you can imagine.