Flagstone patios and natural stone paths

Real flagstone is natural stone, and it comes off the pallet in irregular slabs of uneven thickness. Each piece gets cut to its neighbor with a saw and a chisel, so the joints follow the stone and no two patios come out alike. Flagstone-pattern pavers are concrete, molded in a few shapes that repeat across a field. They are uniform in thickness, they lay faster, and they cost less per square foot installed because the fitting time is not in them. We build both. Pattern pavers go in like a paver patio, off a string line with polymeric sand in the joints.

Dry-laid flagstone sits on 3/4" clean crushed base, 8" to 16" deep depending on the soil and the application, compacted in lifts, with a thin screeded bedding course and joints filled in stone dust or gravel. Nothing is glued, so a stone that settles gets lifted and re-bedded, and water drains through the joints instead of standing on them. Mortar-set flagstone goes over a poured concrete slab on a mortar bed with grouted joints. It reads tighter and sweeps cleaner. It is also rigid, so it is only as good as the slab under it, and a slab that cracks cracks the grout line with it.

Thickness is the spec people skip, on a patio or a flagstone path. Dry-laid stone carries its load across bedding sand and gravel, and bedding gives a little, so a thin slab flexes and snaps the first time weight lands on an unsupported spot. The broken piece does not lift out on its own, because the neighbors were cut to fit it. Thin stone belongs on a mortar bed over concrete, where the slab carries the load and the stone is the wearing surface. For dry-laid work we buy the thicker material and the proposal names what we are buying.

Joints are where a flagstone patio fails first, and a Bozeman winter is what finds it. Dry-laid joints take stone dust or gravel, swept in and topped up after the first season, and they drain, which matters when meltwater crosses a patio in March and refreezes that night. Mortared joints do not drain, so the patio gets pitched away from the house, around a quarter inch per foot. Flagstone-pattern pavers sidestep most of that with uniform thickness and polymeric sand. Every edge we build gets a poured concrete curb below finished grade. No plastic edging, no steel.

Seat walls get built into the patio instead of added later, so the base goes in once and the wall sits on it. The core is mortared, drainage goes in behind it, and the cap is flat and wide enough to sit on without catching your leg on a lip. Caps are laid with a slight fall so water runs off the face instead of standing in the joint and freezing. A gas fire table gets a level pad set into the field of stone. Fireplaces and heavier stonework are on our masonry page.

The flagstone we lay is quarried regionally: sandstone and quartzite in tans, rusts and grays. Color runs in lots, and two pallets of the same stone can land a shade apart, so we open several at once and blend off them. The field gets laid out dry before anything is bedded, then cut. Stone can carry a lead time, so it gets picked at the proposal stage, not the week we start. A flagstone path or a run of slab steps uses the same stone. We lay it in Bozeman, Belgrade, Four Corners, Gallatin Gateway and Big Sky.