Curving MDF skirting board around bay windows

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I've seen a few questions posted about curving skirting board around bay windows, so I thought I would post my solution in case anyone is trying to do the same.

This worked for me using MDF skirting board.

Attempt 1

I created a "jig" on the floor of the room and over the course of a week, I kept wetting the skirting board and adjusting the jig to apply more curvature to the board. This did result in a curved board.

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The problem with this approach, is that although the board was curved, it didn't match the curve of the bay window. Additionally there was no flexibility to push in different parts of the board at various positions along it's length to fit the bay.

After a few attempts of trying to get the board to fit it snapped.

Attempt 2

Following the first attempt I then decided to kerf cut the back board. Most information I saw on this recommended to cut the front of the board and fill, but I thought I would get a better finish filling the top edge of the board rather than cuts on the front face.

20210626_155118.jpg


I set my circular saw depth to be just shy of the width of the top edge of the board. Using a square I then marked off at approximately 10mm intervals along the back of the board with pencil marks.

I then cut the board at the set depth along these lines. I didn't really bother to do neat job, for example running the circular saw against a straight edge for each cut. This took quite a long time but it did result in a very flexible board which could be matched more or less to the curve of the bay window.

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Here is how it looks when screwed into position. The hardest part from here was getting it cut to the correct length. I had to keep trimming a bit off one end with a 45 deg. mitre and offering it back up to the wall. I was convinced it would snap again but it didn't. Likewise, I was concerned I would end up taking too much off the board leaving it too short for the curve.

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I was a bit worried about the gaps against the wall in the top of of the board but it was easy to fill these in, and the kerf cuts using wood filler and finishing off with decorators caulk.

The next hardest part was cutting the smaller boards (left of the curved board on the above picture), and mitring the edge to fit. This was just trial and error on a piece of scrap until I had the saw set correctly.

Here is how the finished result looked after filling and painting.

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I used a combination of 2 pack wood filler and fine surface filler. I used the wood filler to fill the deeper parts of the kerf cuts and where I had counter sunk the screws. I then finished off with a fine surface filler as I personally find this easier to sand down.

I was slightly worried the not exactly perfect curve would be noticeable, however now the radiator is hung and carpet fitted your eye is not drawn to it. I finished off the top of the bay with a ledge also from MDF.

What I would do differently next time:

- Put a 10mm pen mark on my square to make drawing the lines at the 10mm interval on the back of the board faster.

- Mitre glue the left / right smaller sections to the curved section where the board returns into the room.

Happy to receive any feedback as I have another identical room where I need to do the same in the coming months.
 
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I did this using pine wood for my bay about 20 years ago. I cut numerous slots as you have done and then continuously wetted the back each day for over a week. A few test bends until I was confident it would bend to the approximate curve I needed to get it set up. I then set up a couple of blocks screwed to the floor with a metal plate placed in front of the blocks. The metal plates had a threaded holes drilled in to them and a length of bar with two nuts on the outer end was threaded through each block, (think I used either 10 or 12 blocks to keep the curve tight). On the end of the bar which would come into contact with the wood I had a narrow but strong plate attached. By gently bending the skirting into shape to fit behind the clamps I was then able to increase the pressure each day, (I was still spraying them with water each night and allowing it to soak in), until it was about as perfect as I was going to get it. I then left it in place for over a week during which time I introduced gentle heat into the room to slowly allow the wood to dry out. I should say that I fitted wood blocks in the mortar gaps of the brick work before starting the bending operation. I then drilled and countersunk fixing holes in line with the wooden blocks. Once they were secure I gently released the blocks a little at a time over 3 days watching for any gaps appearing. Then, as you, filled with filler and finished with decorators caulk. It was still there when I sold the house nearly 10 years ago.
 
That beats the hell out of soaking MDF and hoping it will flex enough (y)
 
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Template for the curve, 3mm mdf, glue each piece together around the curve to the required thickness, once dry form the chamfer?
 
How do you deal with a torus or a Grecian ogee, though?
 
On a related subject, I watched a DIY type programme the other week and the bloke knocked up a wood steaming contraption out of some 100mm drain pipe and a wall paper stripper and when the strips of wood came out they were like rubber and he bent them into some crazy shapes.

So 150mm drain pipe may hold skirting .....
 
Depends on the species, @^woody^. Not all species bend all that well. If you steam timber before machining it, it needs to be thoroughlty dried before hand to get a clean cut - if you pre-machine it some profiles won't bend without major risk of cracking or failure. Either way I see that as slowing installation down a lot

You do know that with steam bending you ideally need a steel strap jig for safety? Even then you still need to accept a percentage of failures.
 
Somewhere I have a photo of a 100mm wide strip of MDF left out in the rail over the weekend - it has bent like a pretzel
 
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I thought that plaster was run in situ for those kinds of jobs.

My house has hockey stick returns in the bay. I used plaster but to be fair it was only a chamfered edge.

I am not a chippy but I have been on site where the film set chippies just laminated lots of layers of plywood on a template and then machined the requisite profile a few days later.
 
opps said:
I thought that plaster was run in situ for those kinds of jobs.
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I've seen it on houses as late as the 1930s, but I can't recall seeing it on post war housing

opps said:
I have been on site where the film set chippies just laminated lots of layers of plywood on a template and then machined the requisite profile a few days later.
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I haven't done much set work, but there is a world of difference between what will pass muster on a stage or film set and what is acceptable for a paying job, where the client might well see a flaw numerous times (to the point of it becoming a real bugbear for them). The technique used is very similar to the way we used to build curved counters - build a perfectly flat and level assembly floor, build a series of vertical ribs, clad them with several layers of thin plywood, sand-off and finally clad with laminate. The machined bent laminated plywood (or MDF) is actually dog rough and often needs a lot of filling and sanding to make good.

I've often thought that the main body of the skirting could be formed with two 9mm skin of bendy MDF and the moulding on top could then just be band sawn out of knot-free softwood, template routed to a curve (or possible even routed using a large trammel) and then the profile routed and finally tacked onto the bendy MDF body.
 
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