How to Lay a Flagstone Walkway Using Concrete

Using a concrete base for the support of a flagstone walkway ensures that the flagstones remain level, regardless of any shifting in the soil beneath the flagstones. With concrete as a base, there is more work involved in creating the walkway than when a bed of sand is used as the base. Before placing the first flagstone, you'll need to create what amounts to a concrete walkway beneath, complete with creating a wooden form for the concrete and allowing time for the concrete to cure hard enough to hold the weight of the flagstones without sagging. Though this process extends the installation time, the completed walkway should last decades without any movement in the stones to cause damage.

Wooden stakes
Rubber headed mallet
String
Tacks
Spade
2-by-4s
Circular saw
Wood screws
Screwdriver
Tamper
Gravel
Concrete mix
Wheelbarrow
Wood screed
Steel trowel
Thinset mortar
Flagstones
Carpenter's level
Grout bag

Instructions

- 1
  Mark out the area for the walkway with wood stakes driven into the ground every 3 feet along the two edges of the proposed walkway. Connect the top of the posts with a string tied around them to help you note the walkway's borders.
- 2
  Measure the depth of the flagstones with a tape measure. Dig a foundation hold along the staked borders of the walkway with a spade to the depth of 6 inches plus the depth of the flagstones.
- 3
  Remove the wooden stakes and strings. Build a concrete form within the foundation by lining the sides with 2-by-4s cut to the same height as the walkway surface using a circular saw, and joined together with wood screws.
- 4
  Compress the soil at the bottom of the foundation with a tamp. Fill the foundation with a layer of gravel 2 inches thick, and then tamp down the gravel.
- 5
  Mix a batch of concrete in a wheelbarrow. Use the spade to turn the dry mix in with the amount of water suggested by the concrete mix manufacturer. Scoop the concrete mix into the hole, creating a layer of concrete 3 inches thick. Drag a screed across the top of the concrete to level it. Cut expansion joints across the concrete every 10 feet about 1/2-inch in depth to allow the concrete to expand without cracking. Let the concrete cure for 24 hours.
- 6
  Mix thinset mortar in a large bucket. Add enough water to the mortar to create a thick, spreadable paste. Spread the mortar onto the concrete in a layer 1 inch thick using a steel trowel.
- 7
  Place the flagstones onto the layer of mortar, and then use a rubber-headed mallet to tap the flagstone level. Leave a space of about 1/4 inch between each of the flagstones. Wait 24 hours for the mortar to cure. Check flagstone level with a carpenter's level. Make any adjustments while the mortar holding the flagstones in place is still wet.
- 8
  Fill a grout bag with thinset and use the bag to squeeze the mortar between the placed flagstones. Fill the gaps between flagstones to the surface level of the stones. Allow the mortar 24 hours drying time.
- 9
  Remove the wooden frame around the walkway, then fill the space left with some of the dirt removed to create the foundation hole.

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