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How to Install Picture Frame Moulding on Walls

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DIY picture frame moulding on light gray walls in entryway

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Before we officially dive into installing picture frame moulding, or any wall trim molding, let’s talk about the elephant in the room…

Is it moulding or molding?!

It doesn’t matter. They are the exact same thing. Moulding with a ‘U’ is generally regarded as the British spelling, but for some reason, that’s the spelling I prefer (even though my spell checker isn’t a fan).

In this tutorial, we’ll walk you through how to apply picture frame moulding to your walls. We opted for a more modern take on the classic design by adding two stripes of moulding to the lower quarter of the walls.

You can use this tutorial for traditional picture frame molding, the design we completed, or any other design your heart can come up with. The installation principles are the same.

Alright, let’s start DIYing!

Tools

What You’ll Need

How to Install Picture Frame Moulding on Walls

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STEP 1: DECIDE ON A DESIGN AND MEASUREMENTS

Start by brainstorming your design. For our wall, we chose to do a more modern take on a traditional picture frame moulding. Rather than having smaller boxes on the bottom and larger boxes up top, we opted to have two stripes of moulding that spanned the bottom of our wall.

As you’re planning your design, first decide on the number of boxes you want to have and the spacing you want between boxes. We left 5.5″ between our boxes and from the sides of the walls.

If you want your boxes to all be equal width, use the following equation to determine how wide your boxes should be:

(Width of wall – (space between boxes * (number of boxes +1)) / number of boxes

Once you have your design in mind, I recommend grabbing some painter’s tape and mocking up the entire design on the wall.

taping wall trim design on wall

This is also a great way to get the general dimensions for awkward areas like angled walls. Rather than trying to figure out all of the math of a triangle, you can tape it up to your liking and then use the length of the tape as your measurement.

Speaking of angled walls, if you have one and you want to trim off a triangle, you can use this online calculator to help you determine the angles you’ll need to cut your trim at.

STEP 2: PREPARE

Start by marking all of the studs along your wall. Though you aren’t limited to nailing only into studs, you’ll want to nail into them whenever possible.

Not only will nailing into studs make your trim more secure, it’ll also limit your chances of hitting something (plumbing or electrical) behind the wall.

Now that you have your studs marked, mark how high your bottom-most boards will go. If you have a laser level, you can just set that up to use as your mark.

Next, make a spacing block jig. You’ll use this to get consistent spacing while nailing up your pattern.

For our design, we needed two different boards. We needed one that was 1″ wide and one that was 5.5″ wide. We just used a 1×6 board for the 5.5″ piece.

Finally, sand your moulding if needed. Some pieces will be super smooth and some won’t be. Sand until all the boards are smooth. This will help with painting later.

STEP 3: NAIL YOUR BOARDS TO THE WALL

General installation tips

To install our trim, we’re going to use 5/8″ nails. They’re really short, so you’ll need to be sure to nail through the thinner areas of the trim to get a good hold.

The main reason for using such short nails is that we want to avoid accidentally hitting plumbing or electrical that might be hiding behind the wall. The less the nail pokes through the back of the drywall, the less likely we are to hit something.

That being said, it’s still not guaranteed that you won’t hit something. Install molding to walls at your own risk!

As you nail into the wall, hit the studs whenever possible. When you aren’t able to hit a stud, position your nail gun at alternating angles (up, down, right, left). By alternating the angles, it’ll help lock the moulding into place.

nailing trim at an angle

Note: I don’t like to use or recommend using construction adhesive on any accent walls. If you apply construction adhesive to drywall and then later decide you want to take down the accent wall, you’re going to have A LOT of drywall repair on your hands. I prefer to rely on nails and caulk. If you nail your boards in and they seem a little loose still, that’s okay. Once we apply caulk to either side, that will keep it from shifting around.

Installing the bottom pieces

Start with your bottom pieces, making sure they stay level as you go along your wall. If you’re doing the same design as us and your wall is longer than 8′ wide, you’ll need to splice two pieces of moulding together.

To do this, cut the side that is going up against the wall at a regular 90-degree angle. Then cut the side that is going to be joined with the second piece of moulding at a 45-degree bevel.

Once you install that piece, measure two or three times to get the length of the next piece. If your cut line isn’t smooth, be sure to sand it before installing the moulding to the wall.

When installing, slide the angles together until it looks seamless and then nail into place.

Installing picture frame moulding

Once we installed both the bottom pieces, we moved onto the boxes. For each piece of the picture frame moulding, you’ll cut both sides at a 45-degree mitered angle.

Start with installing the bottom piece of the first frame. As you nail it in, make sure it’s level and placed the correct distance from the neighboring wall. Ours was 5.5″ from the wall, so we used our spacer block as a guide.

picture frame molding lined up with laser level line

Next, install the vertical boards. To do this, simply line up the angles with the bottom board, make sure it’s level, and nail into place. Keep moving the level up higher as nail up the boards.

Because walls aren’t often perfectly level or straight, it’s important to rely on your level while installing these first vertical boards rather than using the spacing block.

You can also use a speed square to help make sure the corners are square before you start nailing. To do that, grab your speed square and place it in the corner of your picture frame moulding, making sure that it’s flush with both the horizontal and vertical moulding.

Finally, install the top piece of the picture frame moulding. If you kept things level as you installed the vertical moulding up the wall, your top piece should fit snugly right in between your two vertical pieces.

If you’re concerned about gaps, you can stop nailing your vertical pieces with about 2′ left to the top. Then add the top piece and then you can finish nailing in the vertical pieces. Leaving the room at the top unnailed will allow you to pull it in or out slightly for a good fit.

Continuing installation

Now that the first box is installed, we can install the box right next to it. This is when the spacing blocks start to come more in handy.

You’ll repeat the installation as we just did, but this time, you can use the spacing block instead of a level for the first side. Keep the spacing block tight between the vertical board on your first box and the vertical box on your second box and nail it all the way up.

Once you have all of the main boxes installed, it’s time to add the thinner molding!

This thinner moulding can be difficult to cut on a miter saw, so I’d recommend using a handsaw and a miter box if you have one available. If you don’t have one available, please take a moment to set up a sacrificial fence to safely cut the thin trim.

Once you have things cut, grab your 1″ spacer block and press it up against the inside of one of your picture frame boxes. Then press the thinner moulding up against the spacer block.

nailing up thin picture frame moulding

Keep the spacer block snugly sandwiched between the moulding as you nail it all in. No need to use the level here. We’ll just rely on the spacing block (but that means you have to be precise with your measurements).

STEP 4: WOOD FILLER + CAULK

These two simple steps are what are going to take your project from looking good to looking a lot more professional, so don’t skip them!

First, add wood filler to any nail holes. You can also add it anywhere that two boards meet (i.e. corners).

When adding wood filler, generally you want to overfill any gaps or holes and then sand off the excess. With this project, you’ll want to barely overfill them so that sanding is quick and easy. It can be difficult to sand in the grooves on the moulding, even when using a sanding block.

Once your wood filler is sanded, wipe off any dust that’s on your moulding.

before and after of wood filler on moulding corners
Before and after wood filler of the gap between our angled pieces. Not pictured: also fill the nail holes.

Apply caulk anywhere the moulding meets the wall. This will not only get rid of the appearance of any gaps, but it will also help further secure your mouldings to the wall.

Apply a thin bead of caulk between the moulding and the wall and then wipe the caulk smooth using a wet finger or a baby wipe.

caulking moulding

STEP 5: PAINT

Once the caulk has dried, you can start painting! We painted ours Sherwin William’s Frosty White in a flat finish. Many people like to use a satin finish on moulding because it’s easier to clean, but it will show more imperfections.

There you have it! Now you know how to install wall trim molding! We did a more modern take on a classic picture frame moulding, but this installation technique will work regardless of what trim design you choose. The only difference might be the nail size. If you have a less dainty molding, you might consider longer nails and/or using a 16 gauge nail gun instead.

If you want more accent wall inspiration, be sure to check out these posts:

DIY Geometric Accent Wall | DIY Wood Accent Wall | DIY Shingle Accent Wall (this one is SUPER cool)

modern picture frame moulding with abstract art and candle sconces in entryway
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  1. Christin says:

    I totally needed this tutorial! I plan to do this in our guest bedroom, but my success with perfect right angles to actually match to make a frame is subpar. I have a miter saw, but do I need a better blade maybe? No 45 degree angle has matched up.

  2. Olivia says:

    Looks great!!! Did you do Big boxes on all walls in the room? I’m trying to decide if I should just do an accent wall vs all walls in the bedroom.

    • Zoe Hunt says:

      Hi Olivia! You can’t go wrong either way. Personally I would probably do all of the walls in your bedroom, but it’s up to you. This was in our entryway so we did put boxes on both walls in the hallway.

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