Riven slab-gravel “stepping-stone� path

[PeterG]

We are creating a pond outside the house. The ground slopes away, so we have raised the level of the soil by up to 250mm to accommodate this. We are extending an existing path which consists of large Stonemarket Millstone flags surrounded by 10mm pea gravel. This path has gaps around 25mm, but wider at the outer edge of a curved section and was laid by contractors.

We have bought more 600x750mm Millstone flags and are planning to lay them in a gradual curve down to new steps leading down to the lawn. We have laid a sub-base of MOT#1 in layers as you suggest to shuttering set at a width of 1200mm and are now around 50mm below the desired level. An entry in the archive for a similar problem (“Combination slab & gravel�, Riven slabs combined with gravel in-between the slabs) suggests using a semi-dry cementitious bed for the slabs: 1:10 cement:grit sand.

We are planning to lay the slabs cross-wise with a similar spacing, so between each slab we will have a gravel-filled gap of 25-50mm but we will also a have gravel-filled gap between the slabs and the edge of the sub-base. As this gap will be 225mm wide, we are worried that cement-sand will not be strong enough to stop the possibility of the edge of the slabs dropping under use and are wondering whether we should use concrete or a stronger mix for the bedding?

P.S. Thanks Tony for your work on this site; it’s a great reference point.

[lutonlagerlout]

concrete will be better, peter,especially at 225 mm wide
otherwise your premise sounds fine
LLL

[Tony McC]

Using the 10:1 mix as a laying course for the flags will be fine, but remember to bring up the mix at the edge of the flags to prevent them slipping sideways (what we call "lateral movement")...