Expansion Joint Advice for Concrete Driveways and Sidewalks
Mark McCullough clears up some concrete driveway and sidewalk joint confusion
We have expansion joints in the poured concrete of our driveway and sidewalks. Our builder’s written instructions say to fill the joints with sand and cover it with joint compound. What type of sand and compound should we use?
—George Earhart, Galena, OH
Neither one! Joint compound would start falling apart after the first rain, and all that sand would quickly become an ant farm.
Before I go into what you should do with these joints, let me clear up some confusing vocabulary. Expansion joints are the full-depth gaps that separate large concrete slabs from one another. They allow the slabs to move independently with changes in temperature and soil moisture, or due to uneven settling. Without these joints, a slab would end up with big, jagged, uneven cracks wherever the stress was greater than the strength of the concrete.
These joints do need to be filled in order to exclude dirt and debris that might restrict slab movement. I like to use ¾-inch-thick asphalt-impregnated fiberboard strips for that purpose. They remain resilient even when tightly crushed and do a good job of keeping out debris for many years.
Control joints also deal with cracks, but only the small ones that form as the slab shrinks. These joints are partial-depth cuts made in the surface of a slab when the concrete is still wet. They’re only an inch or so deep—you can see their bottoms—and there are usually many more of them in a slab than expansion joints. Control joints provide a place for cracks to run so they won’t be visible. There’s no need to fill these joints with anything.