Installing Crown Moulding - Part Three: Curved Walls

Home Improvement: Placing crown moulding on curved walls can seem like an impossible challenge – follow these simple tips to achieve great results.

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Installing Crown Moulding - Part Three: Curved Walls



Photos by Roger Knapp;  Illustration by James Provost

In this, the third part of the series, I will discuss the making and installation of crown moulding to a curved concave and convex wall. The techniques that I will discuss and have used will assist you in the cutting and buildup of curved crown moulding. The procedure can also be used to make curved crowns and other mouldings out of hardwood for use on cabinetry.

Before I begin, as with most home improvement projects, there are other options a woodworker can consider before they decide to cut and glue expensive wood themselves, although most of us live for the challenge. There are two options that I am familiar with. The first is a crown that is flexible and can be stretched to conform to the shape of the wall. The other is a rigid moulding that is poured in a mould to the correct crown profile and to the radius of the wall. Both of these options are expensive and limited to crowns that will be painted and they may be difficult to match to an existing profile.

The crown job in our home involved a short convex wall in the lower washroom and a long concave wall in the staircase. I will begin with the short convex wall and then follow with the procedure to create a curved piece for the long concave wall.

The method I used for the convex wall is called ‘slice and dice’ or lamination and involves cutting two identical mouldings and then re-gluing them on a form.

Begin by taking a rough measurement of the curved wall and adding 6" to each end.

Cut two equal lengths of crown to that measurement.

You need to create a filler behind both crowns by gluing strips of similar material to the back. By using a similar material you will reduce the chance of creating stress and twisting action during the shaping on the mould.
 

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Fill the back – Create a filler by gluing strips to the back of the crown.
 
You now need to trim the filler to the spring angle of the crown (38/52) so set your table saw to the correct angles and rip the filler so you have two pieces.

I have divided both crowns into five segments, each about ⅜" wide. This thickness is not critical but may have to be reduced to ¼" for a tight radius. You only need to consider two things as you are creating these spacings. First, it needs to be thin enough to bend easily, and second, the saw should not cut into the sharp profile of the moulding. Try to stay at least 1/16" away from the edge of this profile. Label the crowns ‘A’ and ‘B’ and pencil in an ‘S’ for each scrap segment. Now, because you will be cutting and keeping every second piece to restack to the original thickness, you need to determine the width of your band saw kerf as you are making one crown moulding out of selected segments.

I determined the width of my saw kerf to be .058", which happens to be the thickness of the snap ring.

All cuts are performed so that the cut off piece falls away from the blade. Set up the fence the width of the crown less the thickness of the first waste segment.

Because the fence needs to be moved after every cut, I use the combination square as an adjustable stop and index it into the mitre slot.
 

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Mark carefully – Mark out the saw cuts and identify the segments that will be kept to build the curved crown.
 
Follow the following steps:

1) Take piece ‘A’ and remove the first segment (approx ⅜") and set it aside as scrap.

2) You now need to move the fence the width of the saw kerf by using the combination square and the spacer or washer that you determined was the thickness of your saw kerf. Index the body of the square in the mitre slot, place the spacer against the fence and extend the blade till the spacer is contacted and lock the square. Remove the spacer, loosen the fence and move it towards the saw blade till it contacts the square, which is still indexed, and lock it in place.

3) Take piece ‘B’ and make the cut. This piece you keep. It should be the thickness of the scrap piece plus the width of the saw kerf. Reposition the fence approximately ⅜" for the next cut on the same piece ‘B’ and scrap the off-cut.

4) Reposition the fence the width of the kerf as before. Now take piece ‘A’ and make your cut and keep the off cut.

5) Reposition the fence again, about ⅜", and make another cut on piece ‘A’ for the scrap cut.

6) Continue the procedure until all cuts are done.
 

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Know the kerf – Use a combination square and a washer to reposition the fence after every cut.
 

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Cut with care – Locate the saw cuts to avoid cutting into the sharp profiles of the crown.
 
After a few more cuts, your moulding should be ready for glueup after you clean up the roughness of the saw cuts. It is not necessary to have smooth surfaces and do not run the segments through the planer as that will change its final stack height.

The convex curve gluing form that you need to build should be the height of the crown, by 12" wide and the length of the crown pieces. I took a profile of the wall with ¼" plywood and shaped it with a rasp until it conformed to the wall at a point three inches below the ceiling and then transferred that shape to the gluing form and cut it out on the band saw.

Because it is unlikely that the curve of the wall will be a perfect arc and symmetrical, it is important that you mark the topside and the underside of the gluing form you just made and place it upside down on the bench because you will be gluing the crown upside down.

During the glue-up I found it easier to glue and clamp one or two pieces at a time instead of all at once. Placing a brad nail at one end also helped keep the moulding aligned.

With the crown still attached to the form, clean the dried glue and fill the joints with Spackle drywall filler. Sand the profiles smooth with curved sanding blocks. Take your time here because the glossy paint top coat will highlight any dips and hollows. This step is not as difficult as one might think because you are only filling the saw kerf and following the profile with the sanding block. Seal the surface with two coats of shellac.

Once the crown is off the form, set the band saw table to the spring angle and cut the filler piece away from the back of the crown to create a curved crown moulding. This is performed freehand on the saw. If the filler is not removed, it will interfere with the corners and the crown will not fit tightly to the wall and ceiling.

You will find the curved crown to be quite rigid and it can be installed using normal procedures.

I find that cutting the angles on the ends of the curved piece first and tacking it into place and then fitting the straight pieces to it works best.

Having completed the convex curve, I was now faced with a long concave wall over the staircase for which I could not possibly make a glue form. The solution is a modification of the previous method and now I use the wall as the form.

This method calls for only one moulding to be cut and laminated to form the curved crown. I selected a crown moulding that was 2 ½’ longer than the arc. This length would give me an extra 12" at each end of the curve plus a piece 6" long that I could use for fitting. This extra length will ensure that the lap joints on each end will be located along the straight section.

Take this moulding and fill the back as before to form a triangle shape that can be resawn.

In this procedure the filler does not get cut away from the back of the crown prior to installation on the wall, therefore nailing backing strips is not needed on the wall.

Set the fence on the band saw to rip this crown in ⅜" thick segments. Glue wood strips to the face of four segments to make up the material that was removed with the saw kerf. This is to ensure that the segments will restack to the original height. I had some shop sawn veneer available but you can saw strips on the table saw to the correct thickness.

I then made cross cuts with a back saw every 2" through those strips. This allowed the crown to conform to the curve of the wall.

Before you fit this curved crown to the wall, you should have installed a straight section up to 12" from the start of the curve, and it must have the under-lap of the scarf joint cut on the end.

Now take all the segments and stack them together to form the crown and hold them together with tape. Make a scarf joint cut to match the cut of the one on the wall (this should be the overlap of the scarf joint). Measure back 6" and make an identical cut. Set aside this 6" long test piece that is held together with tape. Make the under-lap cut of the scarf joint at the other end crown before removing the tape.

Take the 6" test piece and place it on the scarf joint of the moulding that is on the wall to determine the fit. You will likely find the dry wall filler is causing a misalignment of the crown surfaces. You will need to take the block plane to the back side of the first segment and also the top edges of the next three where they contact the ceiling. Do this with the test piece before performing the same to the entire length of the long crown segments.

Once you are satisfied with the fit, take one segment at a time and attach it to the wall with the brad nailer. You are nailing directly into the top wall plate so use a lot of brads. No glue is required between the segments, but as always the scarf joint should be glued. Check and adjust the fit of every segment at the scarf joint as you build up the crown. A little extra time here will make the joint nearly invisible.

Once the curved moulding is installed you will find the lap joint at the other end to be uneven. I found it quite easy to trim the ends with a sharp chisel to re-establish the lower half of the scarf joint. Continue with your crown installation from this point.

Fill the saw kerfs and nail holes on the curved crown with Spackle drywall mud and sand smooth. Two coats of shellac will seal the surface and it is ready for the top coat of paint.

As with any project, there is a high degree of satisfaction seeing it completed and a lot of pride because you accomplished it with attention to detail.
 

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Match the original – The stack height of the segments must be the same as the original moulding.
 

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Long curved walls – Modified moulding segments used on a long curve without a glue form.
 

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Tips for making a curved crown with hardwood for a cabinet

• Select the two pieces of crown moulding with similar grain pattern.
• Use a similar hardwood material for the filler.
• The thickness of the crown segments may have to be ¼" or less depending on the size of the radii.
• There may be a need to smooth the glue surfaces of the segments using a drum sander or shooting plane to hide the glue joints. This removal of material will have to be calculated into the width of the saw kerf before making the cuts.
• The filler need not be removed if the crown will be mounted on a cabinet.


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Related articles:
Installing Crown Moulding: Part One
Installing Crown Moulding: Part Two


ROGER KNAPP
Roger Knapp