How to Fill Crown Molding Joints in 15 Easy Steps

Crown molding can be a quick and easy way to update any room in your home. Simple yet elegant moldings make an immediate impression when someone enters a room. It also enhances the value of a home.

If you are a DIY enthusiast, you might be tempted to install crown moldings yourself. However, if you are working with crown molding for the first time, it is advisable to seek guidance before starting your project. In particular, joining moldings can be a tricky endeavor.

Let’s take a look at how you can successfully join moldings in 15 simple steps. You can purchase the parts and do this fairly easily as a weekend project if you have the tools and patience. Dive in and see if this DIY project should be on your to-do list.

Filling Crown Molding Joints

Wood expands and contracts with changes in weather. For this reason, you need to ensure proper execution of your molding joints and seams so that gaps do not develop in the coming weeks.

To ensure your crown molding has no gaps, here are 15 easy steps to properly fill the joints in your molding:

1. Cut your first piece of molding and attach it to the wall
2. You might want to miter it at 0 degrees with a 30-degree bevel
3. Apply your adhesive square to the backer
4. Place the backer with the adhesive side against the wall below where the joint will be in the molding, making sure to leave some overlap for the next piece
5. Measure for your next piece of molding and cut accordingly (see below)
6. Dry-fit the next piece of molding until it sits snugly. Cut into small pieces and take your time
7. Apply adhesive to the other half of the backer for the next piece of molding
8. Apply adhesive to the end seams of both moldings to be joined together
9. Press against the wall and slide next to the original molding
10. Butt it up as snugly as possible with the first piece
11. Use brad nails for nailing
12. If necessary, secure the moldings with a chisel and small pieces of wood
13. Use wood filler or putty, depending on the molding, to cover the seams and nail holes
14. Sand the crown molding – you don’t want to see any difference between the moldings

If you do not fill your joints properly, you may see gaps in your crown molding within a few weeks. This means you will have to redo your work. You don’t want that.

Before attempting to fill gaps in your crown molding, you should know exactly how to cut and install your molding. If you need to fill the joints, you need to first attach the molding to the wall. Read on below to see how it’s done.

Cutting and Installing Crown Moldings

Before you begin cutting and installing crown moldings, you need to gather your tools. Having the right tools is half the battle in any DIY project. Here are the tools you will need for your project:

• Miter saw
• Pneumatic finish nailer
• Miter gauge saw
• Electronic stud finder
• Wood rasp
• Sandpaper
• Level
• Tape measure
• Caulk gun

In addition to tools, you will need the materials for the job. These include:

• Crown molding
• Tape
• Wood stain or paint
• Wood shims
• Finish nails
• Pencil for marking
• Binder such as caulk or wood putty
• Wood filler or spackle

Once you have all your tools and materials, it’s time to get to work.

Follow this step-by-step guide to install your own molding:

1. Trim the corners of your molding
2. Measure and mark the wall
3. Cut the first measured piece
4. Cut the next piece to fit an inside corner
5. Understand how the pieces fit together
6. Cut the molding at a 45-degree angle
7. Manage the joint
8. Check the fit
9. Secure the molding to the wall
10. Make miter cuts for the outside corners

Cut the corners of your moldings

Don’t be fooled – cutting the corners will be the most challenging part of this process. This is not a straight piece since it sits at an angle. Here, you should use a miter saw as a miter joint is simply tighter than a bevel joint. If you only have an electric miter saw, that will work too, although not as well. You can also cover any gaps in a coped joint with some caulk and some paint or stain.

Since cutting angles will be the most challenging part of this project, we will go through it step by step. Step-by-step guide:

• Set your saw to cut the molding at a 45-degree angle
• Cut the crown molding upside down
• The ceiling edge (or top edge) rests on the horizontal base of the saw, while the wall edge (or bottom edge) rests against the vertical fence of the saw
• For the inside corner on the left wall side, rotate the blade 45 degrees to the right and save the right cut end
• For the inside corner on the right wall side, rotate the blade 45 degrees to the right and save the left cut end
• For the left side of the outside corner, rotate the blade to the left and save the right cut end
• For the right side of the outside corner, rotate the blade to the right and hold the left cut end against the fence while making the cut

Measure and mark the wall

Measure the wall for the length of your molding. Mark the wall with your pencil to indicate the bottom edge of your molding. This may seem like a simple process, but many people make a mistake here. Make sure to measure correctly so you don’t waste material and time.

Cut the first measured piece

Remember the old saying – measure twice and cut once. This will be a straight piece, so you should cut in a straight line at a 90-degree angle. Both angles butt against the sidewalls.

Cut the next piece to fit an inside corner

Now you need to move the miter gauge at an angle of about 45 degrees and make sure to set the molding in place. For a straight cut, your edges must be pressed firmly against the saw table and the vertical side fence.

Understand how the pieces fit together

If you are not a professional, fitting the pieces together can be confusing. The molding is upside down, so the edge against the vertical fence is the bottom of the molding, and the edge against the table is the top of the molding. It helps to think of the table as the ceiling. Always dry-fit your pieces before attaching them to the wall.

Cut the molding at a 45-degree angle

When you have positioned the moldings correctly, use a 10-inch saw blade to make a 45-degree angle cut. Make sure you are cutting the molding in the right direction. For an inside corner, the bottom of the molding should be longer than the top part of the molding. For an outside corner, the top of the molding should be longer than the bottom.

Manage the joint

Managing a joint can be a bit tricky. Here are some steps to help you with it:

• Trace the end of one molding onto the face of the other
• Darker the leading edge with a pencil, and use a coping saw to execute the cut
• Hold your thumb tight against the side of the blade to guide the saw
• Start slow and make sure to cut at a slight angle
• Cut small pieces at a time

Check the fit

Make sure to compare your piece with a scrap of the molding to detect any gaps that need trimming. Use your coping saw to trim the high points.

Secure the molding to the wall

Now comes the moment of truth. You will bring the molding to the wall and slide the end into the corner. Make the fit as tight as possible and then attach it to the wall. Use your caulk gun to cover any gaps in the joint. Note that you may need another piece of molding to complete the wall.

Here is where you start filling the joints of your molding. During this step, you can use paintable caulk, like many people do. However, some professionals swear by wood putty. Wood putty is convenient if you are using a wood stain on your crown molding. It also works well for woodwork that you want to paint.

Wood putty is flexible, so it can expand and contract with the movement of the wood. Remember to use latex putty if you are using latex paint.

If your crown molding is to have a clear wood finish, you can use solvent-based wood filler or spackle to fill nail holes or minor imperfections. You can either apply it with a putty knife or, for deeper penetration, purchase a plastic tube and applicator tip.

For foam urethane moldings, you can use either latex putty or drywall compound to finish the seams and nail holes. Here is a good rule of thumb for installing crown moldings: use caulking at the edges of the molding and wood putty for filling. This gives the molding a professional look, especially if you use wood putty in the nail holes and finish with a stain or paint.

Whichever filler you use, make sure it can be sanded and painted. You want a strong bond that moves with your crown molding. See above for a step-by-step guide to filling joints in your molding.

Be careful when using a tube of caulk or putty, only cut a small portion of the tip before inserting it into your caulk gun. It should only come out as a thin bead of the adhesive. If you have more coming out, you risk getting it on your crown molding. A thin bead should be all you need. Your gaps shouldn’t be so wide if you cut the pieces correctly.

Making Miter Cuts for Outside Corners

The outside corners need to meet precisely. If they don’t, your entire project will be compromised, and you might have to start over. That’s why measurements and test pieces are so important for installing moldings.

If you make small mistakes, you can use caulk and paint to cover them up and give it a good finish. Nobody will be able to tell. However, large mistakes will be noticeable, so don’t leave large gaps or obvious errors.

Types of Crown Moldings

When purchasing crown moldings, you may have noticed that there are several to choose from. From traditional wood to PVC, there are various materials you could use. It depends on your home and your style. Let’s take a look at your options and the pros and cons of each.

If you have a grand foyer, you might want to use plaster for your moldings as it can be tailored into an artistic, custom style that suits your home. If you’re remodeling a guestroom and don’t want to spend much money, consider opting for a polyurethane type of molding. Many people choose wood trims for the character and warmth they bring to a room, but you should choose the molding that you feel best suits your home or workspace.

Types of Fillers for Moldings

We have discussed the types of adhesives you can use when molding. If you’re still wondering what the best filler for your molding is, here are some basic fillers and their characteristics:

• Caulk – Caulk is good for very small gaps and holes. It shrinks a bit as it dries, so it is not good for larger gaps where the filler needs to maintain its shape. It also cannot be sanded, so don’t use it where it can be sanded. It can be either silicone or acrylic. Silicone caulk is waterproof. It may distort over time.
• Spackle – Good for filling nail holes or filling gaps where you need the filler to maintain its shape. You can also shape it after it dries.

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