Crown molding adds elegance and sophistication to any room, so long as it’s installed with the right backing strips. You install these strips behind the molding to provide a solid foundation and keep the trim tight and gap-free. Here’s everything you need to know about using them.
Why Use Backing Strips for Crown Molding?
Backing strips give you a solid surface to nail or glue molding to your wall, and they’re especially handy for areas missing studs and joists. The extra support helps prevent the molding from sagging or separating from your wall over time.
Using backing strips can also make the crown molding installation process more precise. Some homes have uneven walls and ceilings, but the strips help the molding rest straight and even. They also create precise angles at corners for a more professional look.
Pro Tip: As TOH general contractor Dave explained on a This Old House project in Brookline, adding a wider nailer strip serves two purposes: it increases the bearing area for the material being installed and helps “correct for any framing irregularities that might exist” between the framing and the finished surface — a principle that applies equally to crown molding backing strips.
How to Size Your Backing Strip: To get the correct angle for your backing strip, label the adjacent edges of a square-cornered piece of scrap lumber “ceiling” and “wall.” Stand the butt end of your molding on the face of the scrap and line up the molding’s top and bottom edges flush with the “ceiling” and “wall” edges, respectively. Trace along the back of the molding onto the scrap face and cut along that line — you now have a triangular model for the backing strip’s profile. Use this model to set your circular saw’s bevel angle before ripping your strips.
Types of Backing Strips
There are three main types of backing strips used for crown molding:
- Wood: Wood is the most common backing strip material. It’s affordable, easy to work with, and provides excellent support. Manufacturers often use pine or other soft woods, since they’re lightweight and easy to cut and shape.
- Metal: Metal backing strips are typically made from aluminum or steel. They offer superior strength and durability, making them useful for spaces with high humidity or temperature fluctuations. However, they’re a bit more challenging to cut and install than wood.
- Plastic: Plastic backing strips are lightweight, moisture-resistant, and easy to cut, making them a good choice for bathrooms and other high-humidity areas. However, they may not provide as much structural support as wood or metal.
How To Install Backing Strips for Crown Molding
Start the installation process by measuring the length of the walls where you’ll install the crown molding. Make sure the backing strips are wide enough to adequately support your chosen molding profile. If everything checks, cut the strips to fit.
Next, use a stud finder to locate the studs in your walls and ceiling joists. Use screws and nails to secure the backing strips to the studs. If you’re having a hard time finding studs, or if you need more support, use drywall anchors.
Once the backing strips are in place, make sure they’re level and flush with the wall and ceiling. Make any necessary adjustments before you install your crown molding.
When Joists Run Parallel to the Wall: If your ceiling joists run parallel to the wall — which you can check from above or by making a series of nail holes several inches out from the wall — you’ll need a wood backing strip glued to the wall and screwed to the top plate to act as a nailer. This is especially important because there may be no framing member to catch with fasteners along that run.
Pro Tip: Use construction adhesive to stick the backing to the ceiling, then drive a few screws into the drywall to hold it in place while the adhesive cures. Once set, you can nail the crown’s top edge into the backing strips and its bottom edge into the wall studs — giving you a solid two-point connection for a secure installation.
Common Challenges and Solutions With Backing Strips
Even with backing strips, you may encounter some challenges during crown molding installation. Here are some common issues and how to address them:
- Uneven walls: If your walls are uneven, use shims behind the backing strips to create a level surface. Remember, you want a flush surface for the crown molding to sit against.
- Gaps: You can use caulk to fill small gaps between the crown molding and ceiling. For larger gaps, consider installing a piece of quarter-round molding to create a seamless transition.
- Corner joints: Corners can be tricky, especially in older homes where walls may not meet at perfect 90-degree angles. Use a coping saw to create precise inside corners, or consider using corner blocks for a decorative solution that lessens the need for complex miter cuts.
Finding Your Reference Point: Before installing backing strips, survey the full run of ceiling and wall for high and low spots — even differences as small as 1/8 inch matter. Find the high spot first and mark your level line from there, shimming as needed along the rest of the run. This ensures your backing strips create a consistently flat nailing plane, so the crown molding won’t telegraph any irregularities underneath.
Filling Voids Seamlessly: For gaps where the molding meets the ceiling, joint compound can serve double duty — it helps hold trim in place while filling voids at the same time. Apply it to the joint, press the molding in firmly, and use a spatula to remove the excess. If the compound sinks in as it dries, simply come back and apply another coat until the transition is seamless.
Dealing with Wavy Walls: When your wall has one or more “waves” that would throw off the molding, horizontal furring strips fastened to wall studs through the drywall or plaster can create a flat, plumb nailing plane. In isolated spots on a finished wall, use shims to fill the void. You can also fasten a filler strip to the molding’s back edge to help it sit flat against a not-so-flat wall — the same principle carpenters use when fitting chair rail to uneven surfaces.
