Cutting inside and outside corners on base molding is a tricky process. However, with proper measuring and planning and some cover-up tricks, you will be on your way to cleaning corners on your base molding.
Step One – First Corner Cut
Measure the length of the first piece of molding leading up to the outside corner. Measure the length from the beginning to the inside corner. Begin at this point and cut a 45 degree angle with the miter saw or in the miter box with the inside measurement as the base or beginning of the angle. The wall length should be equal to the uncut, inside part of the molding.
For an inside corner, again measure the length of the wall only, mark it on the piece of molding, then cut the 45-degree angle from that point, using the measurement as the base of the cut.
Step Two – Temporarily Place First Piece
Use painter’s tape or temporary picture hanging putty to put the piece of molding in place without permanently attaching it.
Step Three – Second Corner Cut
On the adjoining wall, measure both the length of the inside wall and the length of the molding. Use a pencil to mark both on the second piece of molding. Place the piece in the miter box or use the miter saw to make the second 45-degree cut. The base of the cut should be at the inside wall measurement and the angle should end at the mark showing the entire length of the first piece, including the miter for the outside corner.
For an inside wall, use the same basic method, but the cut goes the opposite direction. Measure both the length of the wall and the length of the molding and mark both measurements. Using the miter saw, make the inside cut between the two lines.
Step Four – Place the Second Piece
Again using a temporary attachment method, place the second piece of molding, matching edges carefully.
Step Five – Nail in Place
Using finishing nails, nail both pieces of molding to the wall. Make sure to use a stud finder and attach at least one nail for every 4 feet of molding to a stud so that the molding will not bend or warp and create gaps. Use a nail set or nail punch to recess the nail heads of the finishing nails so thaey are below the surface of the molding.
Step Six -- Cleaning up Gaps
After your molding is in place, you can clean up the joints and create a smooth, professional looking finish. The secret to clean looking corners with white molding is paintable caulk.
Use the caulk to fill in any gaps between the wood and the molding. If you have properly attached the molding to studs, the gaps should be small.
Smooth the caulking with a barely wet rag or a damp finger. Use the caulk to fill and smooth nail holes as well.
If the pieces of molding do not line up exactly, use the caulking to create a smooth finish. You can also use the caulk to fill in a gap between two pieces. With the proper use of caulking on a white or painted molding, you can create a professional finish.
For a stained or natural wood finish, use a matching wood putty in the same way.