Installing Door Trim & Baseboard Trim in Our 100-Year-Old Home
- 3 days ago
- 11 min read
Installing door trim and baseboard trim sounds like one of those satisfying finishing projects. You cut a few boards, nail them up, caulk the seams, add a coat of paint, and suddenly an unfinished room looks polished.
Except sometimes the flooring is not quite finished, the hinge is in the way, old trim has mystery nails in it, and a simple project turns into several hours of making it work. That is exactly how this french-door project went in our old house—and honestly, that is real DIY life.
For this entryway, I reused old trim pulled from the house, added decorative corner blocks so I could skip the 45-degree mitre cuts, repaired the flooring at the threshold, and worked around a hinge that refused to cooperate. Here is the full process, including the parts I had to figure out as I went.
What You'll Learn:
Finish flooring at the threshold before installing the bottom door trim.
Decorative corner blocks create a straight-cut alternative to 45-degree mitre joints.
Test trim placement around hinges so the door can still open fully.
Wood filler, caulk, and paint touch-ups turn nailed trim into a finished surround.
Tools & Materials for Installing Trim
To install this door trim and finish the surrounding baseboard trim, these are the tools and materials I used for the project:
Interior door trim moulding (reclaimed from another room in the house)
Decorative corner blocks
Brad nail gun (my go-to for installing door trim and baseboard trim)
Air compressor
Miter saw (although the corner blocks meant every cut was straight!)
Jigsaw (for cutting the flooring patch)
Tape measure
Pencil
Wood filler
Paintable caulk
Sandpaper
Interior trim paint
Paint brush or mini roller for touch-ups
If you're tackling your own trim project, a brad nail gun is one of the biggest time savers. It's ideal for installing both door trim and baseboard trim, leaves much smaller holes to fill than traditional finish nails, and makes the installation process much faster—especially if you're trimming multiple rooms
Table of Contents
Starting With the Door Trim You Have
I used old door trim that had been removed from elsewhere in the house. It was thick, solid material, and after sanding and painting, it was ready for a second life around the french doors.
Reusing older trim can be a great choice when you are working in an old house. It helps maintain some of the home’s existing character, and solid old boards can be surprisingly sturdy. Mine had already been painted, but it was still in good enough shape to clean up and use again.
I also had decorative square corner blocks with a raised bull’s-eye detail. These became the key to making the trim installation simpler.
Using Corner Blocks to Skip the 45-Degree Cuts
Traditional door trim is often joined at the top corners with 45-degree mitre cuts. That can look beautiful, but it also means the cuts need to be accurate. If the walls are uneven, the opening is slightly out of square, or the saw setup is not quite right, those corners can become frustrating fast.
The corner blocks gave me another option. Instead of cutting the vertical trim boards and top board at angles, I could cut every piece straight. The vertical boards run into the bottom of the corner blocks, and the top trim board runs between them.
It is an especially useful approach when:
You want a more traditional or decorative look.
You are repurposing old trim with an existing historic detail.
You want to avoid mitre cuts on a tricky opening.
You are working in an older house where walls may not be perfectly square.
The corner blocks still need to be positioned carefully, but they make the trim layout much more forgiving. I started by thinking through the bottom pieces and then planned how the vertical boards would land against those blocks.
Door Trim Ideas for Older Homes
One of the things I've learned during this renovation is that interior door trim moulding can completely change the character of a room. We chose to reuse the original trim from elsewhere in the house because we wanted to preserve as much of the home's history as possible while still giving it a fresh, updated look.
If you're looking for door trim ideas, there isn't one right answer. Some homeowners prefer clean, modern trim with simple lines, while others lean into wider mouldings or decorative corner blocks like we did. For older homes, I think reusing original trim—or choosing a style that reflects the home's age—helps everything feel more intentional.
The decorative corner blocks also made installation much easier by letting me use straight cuts instead of 45-degree mitre joints, which was a huge bonus for this DIY project.
Step 1: Check the Hinges Before You Commit to the Bottom Blocks
My first problem showed up right away: the bottom decorative block ran directly into the french-door hinge. I had two choices:
Notch the back or edge of the block so the hinge could sit inside it.
Move the block beside the hinge instead.
I went with the second option. By placing the block beside the hinge, I avoided restricting how far the door could open. Notching it might have made the trim look slightly more integrated, but function wins here. A door should still open properly after the door trim is installed.
This is one of those details worth checking before you nail anything. Hold every decorative base piece where it will live, open the door, and make sure hardware has room to move. It is a lot easier than removing a freshly nailed piece later.
Prefer to watch the process? We detail it all in this YouTube video 👇🏻.
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Step 2: Finish the Flooring Before Installing Door Trim
I got ready to nail in the bottom trim piece and immediately realized I could not do it yet. The flooring under that section had been removed when the french door and sill plate went in. Since the flooring needed to tuck beneath the edge of the trim, the trim had to wait.
This was the big reminder of the whole project: install flooring before the final door trim.
The floor was a vinyl plank product in a Pickford hickory finish that we purchased from Home Depot. I like vinyl flooring in a busy old house because it is waterproof through the backing and surface, which is helpful with kids, pets, and the possibility of a leak near an exterior door.
Because the replacement piece needed to fit around corners at the opening, the cut was not a simple straight line. I measured the opening, marked the plank with a straightedge, and used a jigsaw to cut the notches.
I also removed the door from its hinges so the new flooring could extend past the edge without the door getting in the way. It added another task, but it gave me clear access to fit the flooring at the threshold.
Was the flooring patch perfect? No. But it was in place, it did the job, and now the base trim could cover the edge where it belonged.
Step 3: Prepare Reclaimed Trim Before Nailing It Up
Old boards often come with little surprises. In my case, the reclaimed bottom piece still had nails sticking out of it. Before putting it against the wall, I removed them so the board could sit flat and so I would not damage the wall or injure myself handling it.
This is a quick but important reclaimed-door trim checklist:
Pull old nails and staples.
Sand rough paint, splinters, and uneven edges.
Check for cracks or damaged ends before measuring.
Make sure the board sits flat against the wall and floor.
Paint before installation when possible, then touch up after filling nail holes.
Usually we have this all done in advance of trying to install the trim but we must have missed this one.
For additional guidance on working safely with nail guns, OSHA’s nail gun safety guidance is a useful reference. A brad nailer makes this kind of project faster, but it still deserves careful handling.
Step 4: Install the Bottom Decorative Pieces First
Once the flooring was in, I installed the bottom corner pieces. I used a brad nailer and lined each block up against the door opening and floor. Because I did not have nails long enough to go completely through the thickest part of the block, I placed nails through areas where they would still hold securely.
The important part was getting the placement right before fastening. The bottom blocks establish where the vertical door trim boards will sit, so they are effectively the starting point for the rest of the layout.
For the upper blocks, I used a small positioning trick: I put one nail into the lower corner first. That held the block in place while still letting me rotate it slightly. Once I could line it up with the vertical trim board and get it sitting flat, I could add more nails.
Step 5: Measure, Cut, and Nail the Vertical Door Trim
With the corner blocks placed, I measured and cut the long vertical boards to fit between the bottom and top details. This is where the corner-block method really pays off: every cut is square, not angled.
My very official family secret for turning trim that is not on the wall into trim that is on the wall was, of course, nails.
Jokes aside, I used a brad nail gun to fasten the boards in place, working my way along each vertical piece. A brad nail gun is one of my favourite tools for installing both door trim and baseboard trim because it makes the job much faster while leaving small nail holes that are easy to fill before painting.
For a clean result, I held the board flat against the wall, checked that it met the decorative blocks neatly, and nailed it in stages rather than assuming one end was enough. Taking a few extra moments to check the alignment before adding more nails saved me from having to pry pieces off and start over.
If a long piece will not sit flat, do not force it immediately. Check the wall, the edge of the door frame, and the trim itself. In an older home, slight gaps or uneven surfaces are normal—and caulk can handle small finish gaps later, but it cannot fix badly positioned door trim.
Step 6: Add the Header Trim Across the Top
After the side boards were installed, I cut the long header board to span the top of the french doors. It ran between the two upper corner blocks, creating a finished frame around the opening.
This top board is visually important because it ties the entire door trim assembly together. I checked the fit, held it in place, and nailed it once it was aligned with both corner blocks.
At this point, the french-door opening finally looked intentional instead of like an unfinished renovation zone. The dark trim worked with the black doors, while the decorative blocks added an old-house detail that felt right at home.
Step 7: Finish With Wood Filler, Caulk, and Paint Touch-Ups
The door trim installation was essentially done after the boards were nailed in, but the final finish work still matters. I needed to fill nail holes with wood filler and caulk the edges and seams.
Those last details are what make separate boards look like one finished surround:
Fill every visible nail hole with wood filler.
Let the filler dry, then sand it smooth.
Apply paintable caulk along small gaps between trim and wall.
Caulk seams where trim boards meet decorative blocks, if needed.
Paint or touch up the finished door trim after the filler and caulk have cured.
I also trimmed a second door for our main floor bathroom during the project, so the whole room ended up with a matching finished look which was nice after being able to see the door frame on both for the last 6 months.
Should You Paint Door Trim Before or After Installing It?
For this project, I painted most of the trim once before installing it, then came back afterward to fill the nail holes, caulk the seams, and do the final touch-ups. I find this gives the cleanest finish while saving time trying to paint tight corners once everything is attached to the wall.
The same approach works whether you're painting interior door trim moulding or learning how to paint baseboard trim. Starting with a coat of paint before installation means you're only doing the second coat once the filled nail holes and freshly caulked joints are ready instead of painting every board twice while it's on the wall. It reduces the number of opportunities for you to get paint on the wall, especially for me since I don't tape before painting because I find it just bleeds anyway.
Regardless of if you're replacing all of the trim in a room, I'd recommend priming and painting as much as possible before installation, then finishing everything with one final coat once the wood filler has dried and been sanded smooth. It takes a little planning up front, but the finished result is well worth it.
The Real Lesson: Work in the Right Order, Then Keep Going
This project did not happen in one smooth, perfect sequence. I started the door trim, found out the flooring had to come first, removed the door, cut and installed new flooring, removed old nails from reclaimed trim, worked around a hinge, then came back to finish the trim.
That is not failure. That is renovation.
When one step exposes another unfinished detail, it is usually better to handle the underlying issue than try to hide it. The flooring needed to be under the trim. The hinge needed clearance. The old boards needed prep. Taking care of those things made the final result more functional and more finished.
And after a few detours, a few nails, and a lot of persistence, the french doors finally had the door trim they deserved and seeing it all installed and painted made the process well worth it!
Door Trim FAQ
Should door trim go on before or after flooring?
Install flooring first when the flooring needs to run beneath the trim. The trim can then cover the expansion edge and create a cleaner finish at the doorway.
Do I need to cut 45-degree angles for door trim?
No. Decorative corner blocks allow the side and header pieces to use straight cuts, which can simplify door trim installation.
How do I install trim near a door hinge?
Hold the trim in place and test the door swing before fastening it. If a decorative block interferes with the hinge, move it beside the hinge or alter the trim so the hardware has clearance.
What should I do after nailing up door trim?
Fill nail holes with wood filler, sand once dry, caulk small gaps along the edges, and apply paint touch-ups for a clean finished appearance.
Should you paint door trim before or after installing it?
I like to do one coat of paint on the trim before installation, then fill the nail holes, caulk the seams, and apply a final coat of paint once everything is installed. It makes painting much easier and helps create a cleaner finished look.
Can you install baseboard trim before door trim?
You can, but I generally prefer installing the door trim first. Once the door casing is in place, it's much easier to measure and fit the baseboard trim so it dies neatly into the casing.
What kind of nail gun should I use for baseboard and door trim?
A brad nail gun is a great choice for most interior trim projects. It works well for both door trim and baseboard trim, leaves smaller holes to fill, and makes installation much quicker than hammering finish nails by hand.
Can you reuse old interior door trim moulding?
Absolutely! Reclaimed interior door trim moulding can be a great option, especially in older homes. As long as the trim is structurally sound, you can remove old nails, sand it smooth, repair any damage, and give it a fresh coat of paint before reinstalling it.
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