Laying Paving Slabs into Concrete (Without Edging)

The main area of paving is laid in the usual way, on a compacted hardcore sub-base with a bed of grit sand or fine crushed stone. Only the outer row goes into concrete. On areas that take more load, the outer two rows go in. The work usually runs like this:

• Dig out and compact the sub-base across the whole area, plus an extra strip under the edge
• Run a string line along the edge at the finished paving height, following the fall of the area
• Lay a semi-dry concrete under the edge row, stiff enough to shape without slumping
• Tap each block into the concrete with a rubber mallet, exactly to the line
• Form a concrete haunch on the outside, reaching roughly two thirds of the way up the block
• Once the concrete has hardened, lay the inner area, fill the joints and compact it

Why doesn't the haunch go right up to the top edge? Soil or gravel can then go over it so the concrete is hidden. It still grips the blocks firmly from the side.

You may also come across paving where the whole area is laid on concrete. That is a different, rigid construction. It needs a concrete slab, movement joints and properly planned drainage. Don't confuse it with this job.

A haunched edge works well for paths, patios, paving next to the house and smaller areas that only take foot traffic. It also suits paving that runs into a lawn, because you can mow right over the edge. It is handy for curves and irregular shapes too, where a kerb is awkward to follow.

On a driveway or parking space, car wheels push on the edge much harder. Here the haunch is made wider and heavier, the blocks are thicker (usually around 80 mm instead of 60 mm) and the sub-base is deeper. For heavier traffic, or an edge next to a drop in level, a proper kerb is often the safer choice. If the paving belongs to a block of flats, agree the work with the building management or owners' association first. If you are creating access from a public road, ask your local authority or the body that manages the road what approvals you need. Some areas also have rules about how front gardens and driveways drain, so check this locally before you start.

The simplest case is a long straight edge on a well-compacted base, with easy access for a wheelbarrow. These things add work:

• Curves and angled edges, where blocks have to be cut
• Edges along a wall, steps or the house, where the haunch is hard to shape
• Soft, clay or waterlogged ground that has to be stabilised first
• A bigger difference in height between the paving and the surrounding ground
• Two rows in concrete instead of one on a heavily used area
• Poor access, where concrete has to be carried in by hand

In practice the edge is often concreted onto a sub-base that hasn't been compacted properly. The concrete then settles with it, and the outer row cracks or tips outwards. Another common mistake is concrete that is too wet. It slumps, the haunch won't hold its shape and the blocks float in it.

Sometimes the haunch is barely there, just a thin skim. A haunch like that cracks with the first frost or the first heavy load. Take care with the plate compactor as well. If you run it over a freshly concreted edge, or use it without a rubber mat, the outer blocks can come loose or chip. Don't forget the fall either. You can't adjust an edge once the concrete has set, so set a fall of roughly 1 to 2 % on the string line from the start.

Don't lay concrete in frost or in strong heat. Below about +5 °C it hardens very slowly and can freeze. In hot weather it dries too fast and cracks. Protect the fresh edge from direct sun, rain and frost.

You can do this yourself if the compacted sub-base is ready and you have some patience. You will need a string line, pegs, a spirit level, a rubber mallet, a trowel, and bagged concrete mix or a mixer.

1. Check that the sub-base under the edge is compacted and extends at least the width of the haunch beyond the paving.
2. Drive in pegs and run a string line at the top of the blocks, falling away from the house.
3. Mix a semi-dry concrete that holds its shape when squeezed in your hand and doesn't release water.
4. Lay concrete under the edge row only for the length you can finish before it starts to stiffen.
5. Place the blocks and tap them down with the mallet exactly to the string line, keeping the joint width even.
6. Check level and fall with the spirit level as you go.
7. Shape a sloping haunch on the outside with the trowel, up to roughly two thirds of the block height.
8. Clean any concrete off the blocks straight away while it is still soft.
9. Cover the fresh concrete with sheeting or damp hessian and let it cure for the time given by the mix manufacturer.
10. Only then lay the inner area, fill the joints and compact it through a rubber mat.
11. Backfill over the haunch with soil or gravel.

• The edge row runs in one straight or even line with no kinks or steps
• The edge is flush with the rest of the paving, nothing sticks up or sinks
• The fall carries water away from the house and no puddles stay on the surface
• The outer blocks don't rock or tilt when you stand on them
• The haunch is continuous, free of cracks, with no bare gaps under the blocks
• No dried concrete is left on the visible face of the paving
• The joints are filled and the outer joints are not filled with concrete up to the surface
• The haunch is covered and the surrounding ground meets the paving neatly