Choosing the Right Stone

A traditional patio begins long before the first flagstone is set. It begins with the stone itself. In Britain, the most enduring choice is a natural sandstone or limestone flagstone, ideally quarried reasonably close to home — Yorkstone for northern gardens, Portland or Purbeck stone further south, and any number of local sandstones with a soft, mellow face that weathers beautifully over time.

Aim for flags between 25mm and 40mm thick if the patio will take foot traffic and occasional furniture. Thinner stone demands a perfect bed and offers no forgiveness; thicker stone settles kindly and can be re-laid if a corner lifts. Reclaimed flagstones, salvaged from old pavements and courtyards, are worth hunting down if you want a patio that looks as though it has always been there. Their worn edges and subtle colour variation are hard to replicate.

Whatever you choose, buy the whole patio's worth in one order. Stone is a natural material, and batches vary in tone. Ordering a little extra — say ten per cent — gives you spares for cuts and breakages.

Planning the Layout and Drainage

Water is the enemy of any patio, so settle the drainage before anything else. The patio must fall away from the house, typically by about 1 in 60 to 1 in 80 — a gentle slope you will barely notice underfoot but enough to shed rain. Next, check that the finished surface will sit at least 150mm below the damp-proof course of your walls. If it cannot, you need a drainage channel or a gravel margin against the brickwork.

Mark out the area with pegs and string lines, and dig to a depth that allows for your layers. A typical build-up is 75mm to 100mm of compacted sub-base, 25mm to 40mm of bedding mortar, and the thickness of the flag itself. Allow extra where the ground is soft or where tree roots have been active.

• Fall: away from the house, roughly 1 in 60 to 1 in 80.
• Clearance: finished level at least 150mm below the damp-proof course.
• Excavation: sub-base plus bed plus stone, plus a little contingency.

Building a Firm Sub-Base

A patio lives or dies by its sub-base. Spread MOT Type 1 or a similar well-graded crushed stone in two layers, compacting each one thoroughly with a plate compactor or roller. If you hire a whacker plate, pass over the area several times in different directions until the surface rings hard underfoot and no stone moves.

Keep checking the fall as you go with a long straight edge and a spirit level, or a string line stretched taut across the pegs. It is far easier to correct the sub-base than to correct the finished patio. For heavier use, or on clay soils, consider a geotextile membrane beneath the stone to stop fines migrating upward and softening the whole structure.

Laying the Flags on Mortar

Traditional patios are laid on a mortar bed, not on sand. Mix sharp sand and cement at roughly 4 to 1, adding just enough water to make a stiff, crumbly mix that holds its shape when squeezed. Lay a bed about 25mm to 40mm deep for each flag, slightly over-sized, and gently tap the stone down with a rubber mallet.

Work from a corner and keep a consistent joint width — 8mm to 12mm is the classic range for a traditional look. Use spacers or a folding rule to keep joints even, and check every few flags with a straight edge to confirm the surface is flat but still draining. Cut stones at edges and corners with an angle grinder and diamond blade, or hire a bench saw for a large run of cuts.

Pointing and Finishing

Once the mortar has firmed up — usually the next day in dry weather — point the joints with a stiff mix of three parts sand to one part cement. A silver sand or a sand matched to the stone's colour gives the most sympathetic finish. Press the mortar in firmly with a pointing trowel or a jointing iron, strike it smooth, and clean the face of the stone before the residue dries.

Cover the patio with sheeting if frost or heavy rain is forecast, and leave it undisturbed for at least 48 hours before walking on it, longer before moving furniture. Brush the surface clean after a week, and consider a breathable stone sealer only if you want to slow staining — though many gardeners prefer to let the stone age naturally, gathering moss and lichen in the joints. That slow weathering, after all, is what makes a traditional patio feel like it belongs.