Q: "Our bluestone walkway is cracking. Is there a better stone we should have used?"
We had a bluestone walkway installed at our house 10 years ago. The surface is flaking and cracking in many areas. We thought this stone would last for at least 25 years. Is there a better stone we should have used?
— Convy, Southampton, MA.
Roger Cook replies: Unfortunately, in nature, not all stone is created equal. Bluestone is a fine-grained sandstone quarried mainly in Pennsylvania and New York. Because it's a sedimentary rock made up of multiple layers of ancient sand deposits, it can be easily split into the wide, flat pieces prized for walkways and patios. But those layers may also flake and split on their own, especially when exposed to cycles of freezing and thawing.
I wouldn't worry about superficial flaking, because that makes bluestone look less like a slab of colored concrete. Continued flaking, however, will eventually weaken a stone to the point where it cracks. At that point, you'll have
to replace it. If it comes to that, I'd recommend getting the best grade of bluestone your local stoneyard has to offer, one in which the sedimentary layers are bonded together more tightly and so won't flake as much. This grade can usually be snapped after first scoring it with a shallow cut. A lower-grade bluestone will have to be cut all the way through because it will flake along the cut line if you try to snap it.
Coating the stone with a sealer may reduce moisture absorption, and thus reduce flaking. It tends to make the surface shiny, a look not everyone likes, so try some on a spare stone first. It also needs to be reapplied periodically. I use sealers mostly when setting stone in concrete. After filling the joints with mortar, I coat the entire surface to prevent moisture from getting through.