DIY Window Mullions

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Guys. I think I have just done my favorite DIY to date.

Do you know what window mullions are? I had no clue that was the “proper” name until I was googling something like “window grid” or “window pane lines” or something like that. I’m telling you, I love google. 😉

Do you remember when I painted the inside trim of our living room windows? I had felt like something was missing with these windows when we had taken off the blinds. I loved the open look, but the windows were just so plain. Painting the trim gray helped a bit, but there was still something missing.

This is after I painted the trim of the windows gray.

The windows on the front of our house are French windows with mullions. All of the windows on the back are just clear glass. I’m sure the builder was trying to cut costs. I started googling if it’s possibly to do your own mullions, and guess what? You can!!

This is what I did:

-Screen Trim (Pine)- 1/4 inch x 3/4 inch
**This was 49 cents per foot at Home Depot. I got 48 feet of this for my project. It comes in 16 foot pieces, so I trimmed them down to twelve 4 foot pieces before leaving the store.

-Clear, thin double sided tape


The hardest part was doing the measurements. What I did was measure the tops and the bottoms of each window going vertically. The top windows’ glass was slightly taller than the bottom windows’ glass, so make sure you measure all of them just to be sure. Then, I measured the tops and bottoms horizontally (again, the bottom windows again had less glass section to cover).

Once I wrote these measurements down, I took the width of the trim (3/4 inches) and subtracted it from the horizontal measurement. Basically, the vertical piece was going to be one complete piece going up and down. The horizontal piece was going to be split into two, with the vertical piece intersecting (meaning that trim width would take up some of the horizontal width). For example: if my horizontal measurement was 28-3/4″, I would subtract the 3/4″ width of the trim and divide that number in half. I would then cut two 14″ pieces to make up the horizontal trim, one piece on either side of the vertical piece.

Whew! Now that the math was out of the way, I got to cutting!

In total, I cut: 4 vertical pieces for the top windows, 4 vertical pieces for the bottom windows, 8 horizontal pieces for the top windows, and 8 horizontal pieces for the bottom windows.

Then I painted

Be sure to paint both sides of the trim.

I started off with the vertical pieces. I put several pieces of double-sided tape on the back and measured where the pieces should go, halfway across on each window.

Once I was confident in my placement, I put pressure on the piece of wood. The good news is you can always remove it if you make a mistake, but this tape sticks pretty well!

Top vertical pieces done! I like it already!

I was doing this in shifts… I’d paint a section of trim, let them dry, hang them while another section of trim was being painted and dried. The painting and drying of the trim was the most time-consuming part.

Once all the vertical pieces were done, I moved onto the shorter horizontal pieces. I did have to trim some of the boards, in the case that the vertical piece wasn’t perfectly centered. I would hold a piece of trim up and mark where it needed to be trimmed and cut it with the chop saw. Making sure these vertical pieces were even with each other across the top and bottom pieces was really important.

I kept working and hanging until… I was done!

And they are still hanging the next morning 🙂

Since I love a little before and after, here you go…

I am in love with it!!!

One tip, if you’re thinking about doing this… double check your windows, if they are ones you like to open and close. Ours can open, but we never open them. I’m not sure how well these mullions would hold up if they were opened and closed much… it might depend on your window. If you have windows that either don’t open or ones that you never open, those would probably be the best ones to do!

This update cost me $24 in wood trim (though I did have some extra) and the double-sided was $6 each (and I got two). So, $36 in total for this update!


One thought on “DIY Window Mullions

  1. Hello there! This is my first visit to your blog! We are a collection of volunteers and starting a new project in a community in the same niche. Your blog provided us useful information to work on. You have done a outstanding job!


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