Stone looks entirely natural! In this project undressed stone was set into a bed of mortar to make a raised edge.
Stone is usually available from landscape supply centres. It is sold by the square metre: the amount you will need can be worked out for you by the supplier, based on the length of your edging. Flat-faced, chunky stones are most suitable for close butted, unmortared joints.
When you are using irregularly shaped stones, you should construct a mower strip if the edge is against lawn. All stone edges should be fixed in place by bedding the stones into a 20-50 mm footing of concrete.
Free-flowing curves can be more easily laid using irregularly shaped stone than dressed blocks.
Natural (undressed) stone
10 mm aggregate (gravel)
1. If you are not working against an existing surface, establish the line by setting a string line. For curved edges lay out a rope or garden hose, or you can sprinkle flour or lime to mark the curve.
2. Excavate approximately 100mm below ground level so that all grass and vegetation are removed. The width of the excavation should be approximately 300mm but will vary according to the size of the stone. If you need to add a mower strip, increase the footing width by 100mm and make a 100mm vertical cut at the front of the excavation.
Laying the stone
3. Lay out the stone approximately 500mm in front of the excavated edge. This will give you a rough idea of how the edging will look. Reposition individual pieces of stone, turning them over or around or swapping them with other pieces until you are satisfied with how they will butt together. If you want the top edge of the stones to be level, adjust the depth of the trench to suit each stone. If the top of the edging is to be irregular, however, the stones can be placed on a flat bed.
4. Prepare the ground for concrete by wetting it to prevent the concrete bed drying and hardening too quickly. It is advisable to mix your own concrete so that small sections can be laid at a time. This avoids the problem of a whole load of commercially delivered concrete going hard before all the stone is laid.
5. Spread a bed of 50mm thick concrete approximately 1m long. Position each stone in turn, using the string line as a guide for an even top edge. Give each stone two or three twists to bed it firmly in place. Make sure each stone is hard up against the edge and also closely butted against the last stone.
6. Fill any gaps with small pieces of stone. Cut them to fit with a lump hammer and bolster and tap them in place. Use concrete at the back of each joint to prevent soil washing out through the joints.
TIP: Using mortared joints
To mortar the joints between the stones, space the stones approximately 50mm apart.
Mix a fairly stiff mortar mix of four parts sand and one part cement. Coloured oxides can be added to the mortar so the joints blend naturally with the rock.
Wearing protective gloves, roll the mix in your hands to make large sausage shapes of mortar. Place each 'sausage' in a joint and use a small trowel to work the mortar in and round the joint.
Use a small paint brush to finish the surface of the joints and then sponge the face of the stone until it is clean.
Fill any narrow gaps between the stones and the hard edge with a sand and cement grout, or sand. Allow the concrete to dry before filling in behind the edging with garden soil.