I love box molding; it’s one of my favorite wall treatments. I also love arches. I had the idea to combine the two and do an arch box molding! I knew one of my upcoming room makeovers was going to be my girls’ bedroom. I had plans to do a modern traditional design style that had castle/princess vibes and would feel sophisticated enough for my 11 year old but still fun enough for my 7 year old. So when it was time to redo the girl’s room, I knew it was just the place for the arch box molding. Plus it was going to go great with the arch barn door I had already built for my girls! I decided to really make this room a wow room! I made arch moldings on the top of the wall with a great chair railing that ran around the middle of the room with box moldings under the chair railing. I have more details about the chair railing install here. This room is perfect, and the girls love it. Be sure to check out the girls’ room reveal here!
With this fun WOW DIY project, you can easily install your arch box moldings with a little time and the right tools and supplies.
Supplies for Making Arch Box Molding
- Base Cap Moulding
- Flexible molding- radial piece. Be sure it is the same width and thickness as the base cap molding. Available at Flexible Moulding Concepts and Flexible Millwork
- Nail Gun
- 1 ¾” Nails
- Laser Level
- Level
- Stud Finder
- Miter Saw
- Miter shears
How to Create Arch Moldings
- I used the same method I used in my bathroom when we did the box molding. I used 4-inch block spacers and checked the level and plumb of each wall and corner. A spacer is helpful when doing molding because it helps double-check if walls are even.
- While working on my arch moldings, I realized my ceiling is not even. There is a ½-inch difference from left to right. I marked the halfway point of the middle box and used my 4” spacer to mark the top of my arch. From the top of my arch to the top of my level chair rail, it is 56 ¼”.
- I marked this same spot on the other boxes to ensure it stays consistent. I did this by moving my laser to the middle of each box and measuring up 56 1/4 “ from the top of the chair rail that I had previously installed. Be sure to mark the top of the arch and then the midpoint with a pencil. It will make a “T” in the center of the top of each arch.
How to Make the Perfect Arch Molding
- Once I found the midpoint it is time to create the arch.
- My arch moldings are 23 ¼” wide. Half that distance is 11 ⅝”. I took a paint stick, drilled a small hole big enough for my pencil near one end, measured 11 ⅝” from it, and made a small nail hole. I marked on my wall a distance of 11 ⅝” straight down from the top middle of where my arch will be.
- I then pushed the nail into the center mark that is 11 ⅝” down from where the top of the arch will be. The pencil hole should be right over the top arch mark, and I simply trace all the arches using the paint stick mechanism I had designed.
- To create the arch at the top of the arch molding, I took my flexible molding, lined it up at the midpoint, and nailed it in. I lined it up around the traced arch and nailed it in until I got to the point where the arch starts to straighten out into the square box portion.
- I had made a laser mark on the wall where I want to cut the molding, so once it reaches the laser I cut it with my miter shears. Once cut, it will line up perfectly with my straight molding pieces.
- After the arches are formed, I nailed the straight sides of the box molding to connect the arch with the bottom piece of trim. I repeated this for all the arches.
- Once the arches are nailed to the wall, I used wood filler before painting to give it a seamless look.
- And then I caulk and fill any nail holes to prep for painting. It is important to caulk around the inside and outside of every box as well.
Tips and FAQs
- Be sure you take the time to caulk in and around every piece of molding; this really does give it a perfect professional finish.
- Use wood filling to fill all nail holes.
- Be sure to order the right size flexible molding that is the same width and thickness as your other molding.
- For this project I used both my miter saw and miter shears. I prefer to use my miter saw when cutting wood or PVC molding. You can use miter shears if the molding is small enough, but the miter saw is much more precise. To cut the flexible molding, it is easier to use miter shears. You can use the miter saw to cut it, but the saw tries to grab the flexible molding and almost chew it, so you have to make sure to hold it very steady and be careful. I highly recommend using miter shears to cut the flexible molding. They cut it much more smoothly.
When nailing the moldings to the wall, do you need to nail them into studs?
I try to when I can, but you don’t need to. This molding is very lightweight, and I am using 1 ¾” nails, so I am not worried about it moving.
How do you create equal boxes?
Use this formula for making your arch boxes. Take the (wall length- total spacing) divided by # of boxes = width of each box.
Can you paint flexible molding? Where can I buy it?
Yes, you can stain it with gel stain, paint it, and it comes in a bunch of different profiles and sizes to match your other trim. I have purchased from Flexible Moulding Concepts and Flexible Millwork. Amazon also carries some sizes and profiles.
There you have it! How to make your own arch box molding like a professional. Need some help with the chair railing install? Here’s my chair railing how-to! And if you love video tutorials, you can watch them here in my girls’ bedroom redo tutorial! Be sure to tag me on Instagram in your finished projects so I can see how amazing they are! #howwedoandyoucantoo
