Covering a Cracked Walkway with Flagstone
Roger Cook explains the best way to cover up a concrete walkway to match a flagstone porch
We want to eliminate an unsightly crack in the concrete walkway off our porch and have the repair tie in seamlessly with the existing flagstone porch floor. Any suggestions? —Becky Knittel, Sharpsburg, Ga.
I'd buy enough matching flagstone to lay an entire walkway over the existing concrete. If the stones are all the same thickness and smooth on at least one face, they could be glued down with an exterior-grade construction adhesive, like the one made by Gorilla Glue. More likely, the stones will have a rough texture and an uneven thickness. In that case, set them in a bed of mortar. Whichever approach you take, the joints between the stones should be filled with mortar.
Before you start, look at how the stones' added thickness will affect the ends of the walkway. At the porch end, the step may have to be rebuilt so that it's between 5 and 7 inches above the new walkway. Anything more or less will be a tripping hazard. You may also need to add a step at the walkway's other end, where it meets the sidewalk.
Once you've figured out the ends, chisel and wire-brush away the loose material around the crack, then scrub the walkway with a power-washer or a brush and a cleaning solution containing TSP or TSP substitute. When the concrete is dry, fill the crack with a polyurethane sealant, such as Quikrete's concrete-crack sealant. If the crack is more than ¼ inch wide, press foam backer rod into it before you caulk.
Now the stone-laying can begin. If you're bedding the stones in mortar, add an acrylic-latex bonding agent like SikaLatex R to the mix to ensure good adhesion to the concrete. Just be sure not to bridge the crack, or you'll end up with fractured stones as the concrete on either side moves. Instead, create a soft joint by leaving a narrow gap directly above that crack. Hide this joint with backer rod and gray silicone sealant. Unlike other sealants, silicone remains flexible and won't be damaged by the sun. To disguise the sealant, blend in some mortar dust collected from a grinder or a saw.
If your new walkway runs past a lawn, you can hide its edge by peeling back the turf a few feet and adding enough loam to raise it up even with the stone edge. Just lay the peeled-back grass back in place and your walkway will look like it's always been there.
—This Old House landscape contractor Roger Cook