How to Install Window and Door Moulding

Make sure that the area is free of dust, dirt or paint residue. Wipe the surface down with a damp washcloth. Ensure that it’s completely dry before starting with installing the door casing.

Check for any gaps in the door frame or walls before you attach the door trim. Fill any gaps with wood filler or caulk.

• Apply the wood filler or caulk with a putty knife for an even layer. Shallow repairs can take up to 15 minutes to dry while deep cavities can take 2 hours or more.
• Sand the area smoothly for a clean surface. Use a fine-grit sandpaper (120-grit or finer) and move it in the same direction as the wood grain.

Cut the trim based on the size you measured. This is to ensure a secure fit around the door.

• Place the casing material on the miter saw’s work table.
• Adjust the angle of your miter saw to 45 degrees for a miterd corner joint. This forms a clean right angle. Slowly cut along the marked line.
• Ensure the cut that you make is straight and at the correct angle.
• Repeat the steps for the remaining casing pieces. For the door, you should have four pieces, two side pieces and two top pieces.
• Repeat these steps for cutting the window casing pieces as well. For windows, you will typically have four pieces. This is determined by the style and size of your windows.

This is an optional step that prevents the casing from shifting gradually.

• Apply a smooth layer of wood glue to the back of the moulding pieces. You can use a construction adhesive for materials that are heavy-duty.
• Apply a fine layer of adhesive using a putty knife or caulk gun and spread evenly.
• Let the adhesive dry completely as per the manufacturer’s instructions before attaching the door trim.
• You can apply adhesive to the back of the window casings if necessary. Follow the same steps for window moulding pieces.

• Align your casing against the door frame and ensure that it’s level and precisely placed. Use a level if necessary. Start at the top and then work your way down.
• Use finishing nails to secure it in place. Space them about 12 inches apart for a secure hold.
• You can drive the nails in with a nail gun instead of a hammer to make it easier and quicker.
• While using a hammer and nails, the wood might split. To avoid this, pre-drill pilot holes.
• Make sure there are no gaps between the moulding and the door frame.
• Repeat these steps to install the remaining door casing pieces.
• The same steps are applicable to installing window trim moulding as well. For this, start at the bottom and work your way up for secure and tight casing around the window.

• Use the miterd corner joints that you cut previously and join them together at a 45-degree angle. This creates a seamless right angle.
• Secure the joint in place with nails and screws.
• If the corners don’t fit well, you might need to adjust the casings by cutting them a bit more.
• The window moulding pieces were also cut at 45-degree angles to make miterd corner joints. Follow the same steps to connect the corners of the window casing.

• Measure the distance between the top edges of the side mouldings. This will help decide the length of the top moulding. Mark the cut line with a pencil.
• Place the casing piece on the miter saw’s worktable and set it to 0 degrees for a straight cut. Clamp the piece in place before you make the cut.
• Slowly cut along the marked line to make sure it fits the side pieces. Use a level to make sure it’s not crooked.
• Attach the top piece to the door frame with nails or screws. Use a nail gun or hammer for this.
• Make sure they fit well with the side pieces. Fill any gaps between the casing and the door frame with caulk like you did before.