Making a Pathway for Wires in a Slab
TOH master electrician Scott Caron explains wiring for kitchen islands
We’re remodeling our kitchen and adding an island. We’d like it to have electrical outlets, but the floor is solid wood over a concrete slab. How do we route wires through concrete without wrecking the floor?
—Erica Venaski, Miller Place, NY
Just so you know, having a receptacle on a kitchen island is not optional; it’s actually required by the National Electrical Code on any island with a countertop bigger than 12-by-24 inches. Your wish is their command.
Running electricity to your island shouldn’t be too difficult, especially if you’re taking out the existing cabinets. And it will only require removing a strip or two of flooring. If you have scraps left over from when the floor was installed, I doubt you’ll be able to tell that any work has been done.
Basically, you’ll have to cut a trench in the concrete for a PVC conduit, which will carry the electrical cable under the floor. The best spot for that trench will be underneath a flooring strip that runs perpendicular from the nearest wall to the spot where your island will be. Cover the neighboring strips with painter’s tape to protect their finish, then run a circular saw lengthwise down the middle of the strip. Make a second cut ½ inch away and parallel to the first; use a chisel and hammer to remove the three scrap pieces. Next, cut out the exposed strip of plywood or OSB that covers the slab, but don’t go all the way through; the concrete will ruin your saw blade. Instead, finish the cut with a utility knife. Save the piece for later.
The next step is to rent an electric concrete-cutting saw with a dry-cut diamond blade. Use it to make four parallel kerfs about ½ inch apart in the exposed concrete. These cuts will kick up clouds of dust, so be sure to wear safety glasses and a dust mask. Having a helper hold a wet/dry vac hose next to the blade will help capture some of the cloud.
Continue making shallow passes down each kerf until they are all at least 2 inches deep. Then break off the tongues of concrete by knocking them sideways with a hammer.
Vacuum the debris out of the trench, then lay in a length of 1-inch-diameter PVC conduit with a 90-degree bell-end elbow on each end. That diameter allows you the option of running up to three cables to your island if you, or a future owner, decide to install appliances there. To fill the trench, dampen it with water, mix a portland-cement grout, such as Quikrete’s Non-Shrink Precision Grout, to a pourable consistency, put it into the trench, and trowel it flush with the slab. Twenty-four hours later, take the strip of subfloor you cut out earlier, spread a moisture-cure construction adhesive over its bottom side, and stick the subfloor to the slab. Now you can glue a strip of replacement flooring to the subfloor. But first, cut off the tag of wood just below the strip’s groove. That will allow you to insert the strip’s tongue in the groove of the neighboring strip and fit the replacement flush with the existing floor.
Shown: Whenever an island is installed in a kitchen, code requires that it be equipped with at least one receptacle. For most islands, two is preferable.
Scott Caron, a licensed master electrician and the owner of Caron Electric in Lexington, MA, appears regularly on TV episodes of Ask This Old House.