How to Install Half Round Molding

Marking a cut on a piece of quarter round molding
  • 4-40 hours
  • Intermediate
  • 0-500
What You'll Need
Tape measure
Small block plane
Six to eight foot ladder
Finish nails
Nail driver set
Pin nailer (optional)
Pin nails (optional)
Air compressor (optional)
Miter box
Miter saw
Silicone adhesive and sealant
Caulking gun
Wood putty
Half round molding stock

Learning and knowing how to install half round molding will not only save homeowners money, it is also a simple and easy task that will add elegance and attractiveness to any room in the home. Choose from pre-fabricated, pre-finished half round molding in plain white, or purchase any natural wood and with a router shape your own. This a simple task that will take at least one or two weekends at the most.

Step 1 - Measure Twice, Cut Only Once

Although this step may sound simplistic, it is often overlooked and can result in a lot of wasted molding. Measure the amount of half round molding required adding two or three feet extra for sacrificial cutting and fitting of angles. Measure each length twice to provide for an exact fit. Use scrap pieces to cut existing angles and trim these to fit before cutting measured lengths. Carefully mark all pieces at location and degree of angle. Never assume that parallel walls will be the same length. Instead, measure every cut individually.

Dry fit all finished lengths before applying adhesive and nailing to walls. Inspect corners and all angles to ensure a perfect fit. It may be necessary to trim angles with a small block plane or a sandpaper block. If a full length does not quite fit the wall, add the additional piece or pieces to complete the installation closest to the corner, as inconspicuously as possible. The seams can be covered with wood putty and sanded smooth.

Step 2 - Finish Molding Before Attaching to Walls

paintbrush dipped in can of stain

Unless pre-finished molding is being used, it is better to apply a finish to natural wood moldings on a work bench then to apply finish once molding has been attached to walls. Applying finish, sanding and clean-up are more easily accomplished on a workbench.

Sand all edges with 220 grit sandpaper to ensure a tight fit. It may be necessary to sand puttied holes where finish nails are inserted to attach half round molding. This should also be done with 220 grit sandpaper and as carefully and smoothly as possible.

Step 3 - Attach Finished Molding to Walls

Fit two angled pieces of scrap half round molding to one corner of the room. When satisfied with the fitting of these two pieces, cut two similar angles on two lengths of molding. Fit one corner of a length of half round molding in one corner, have an assistant hold it in place, and dry fit to ensure a satisfactory fit. If it fits precisely, apply silicone adhesive to molding or corner and nail molding into place.

A hammer, finish nails, and a nail set work well for nailing half round molding into place, however, a pin nailer and pin nails will leave less markings on the molding, and speed up the process of installation. The air compressor used for the pin nailer will also work well to blow away and sand dust from angles and corners before and after installation.