How to Repair an Uneven Bluestone Patio

In this video, This Old House landscape contractor Roger Cook resets an uneven bluestone patio.

Pro Tip: A This Old House landscape contractor explains that sand setting beds are “very hard to get fully compacted, so the stones tend to settle.” When you pull up a settled stone, check the bottom — white marks indicate where the stone was making direct contact with the sand, and if the edges show no support, that’s likely why pieces crack and the patio becomes uneven.

When resetting bluestone, proper base material matters more than the stone itself. As one This Old House project demonstrated, setting bluestone on loam or poorly draining material means it will hold water, and “every winter it’ll freeze and thaw and the whole patio would move up and down.” Using a well-draining pack material — or a mix of stone dust and Portland cement (roughly one part Portland to seven or eight parts stone dust) — creates a stable setting bed that resists seasonal heaving and keeps your repair lasting for years.

Steps for Repairing a Bluestone Patio

Why Polymeric Sand? Unlike plain stone dust or sand, polymeric sand prevents common patio problems. As explained during the This Old House project, “In the past, I’ve used stone dust or sand and you can get ants and weeds growing in the patio. Now, I use something called polymeric sand.” This special sand locks into the joints after misting, creating a firm barrier that resists insect intrusion and weed growth.

1. Stretch a mason’s line across the patio from top of stairs to house. Slip a short length of 1×3 under each end of the taut line.
2. Use a third short 1×3 as a guide block to check the distance between the bluestone slabs and the mason’s line stretched across the patio.
3. If the surface of a bluestone slab isn’t exactly ¾ inch below mason’s line, pry up the slab with a flat bar.
4. If the slab was too high, use a shovel to scrape away some of the stone dust from below the slab. Shovel the excess stone dust into a bucket.
5. In a wheelbarrow mix six parts of stone dust to one part of cement to create a setting bed for the bluestone.
6. Shovel some setting bed onto the substrate and spread it out with a pointed trowel.
7. Set the bluestone slab back into position and tap it down with a rubber mallet. Use the 1×3 guide block to ensure the slab is ¾ inch below the mason’s line.
8. Repeat to check and, when necessary, reset the remaining bluestone slabs located beneath the mason’s line.
9. After resetting one row of bluestone slabs, move the mason’s line over to the adjacent row and start the process over again. Continue until all the bluestone slabs in the entire patio are even.
10. Pour polymeric sand into the joints between the bluestone slabs, then sweep the sand across the surface, filling each and every joint.
11. Use a leaf blower to blow excess sand from the bluestone surface.
12. Take a garden hose and lightly mist the entire patio, including the sand-filled joints.

Understanding the Setting Bed Mix: Note that different bluestone projects may call for different mix ratios depending on conditions. For a dry-set repair like this one, a 6:1 stone dust-to-cement ratio provides enough stiffness to hold the slabs in place without fully cementing them. As one of the This Old House crew members explained, “We’re not trying to set the stone and cement. The cement we have in here is just gonna stiffen up the mix.” This allows for easier future adjustments if individual slabs ever need to be releveled.

Materials

• Five-gallon bucket
• Wheelbarrow
• Push broom
• Knee pads

Tools