Cutting Paving Slabs 4 – 6 cm Thick

First, all the full blocks are laid right up to the edge of the area. The gap along the kerb or wall stays empty for now. Only then are the edge pieces cut, because every edge is slightly different and guessing by eye does not work here.

1. Marking: the block is placed in position and the cutting line is marked directly from the kerb or wall. For curves, a template or a stretched string line helps.
2. Securing: the block is placed on a firm, stable surface so it cannot move during the cut. This matters even more with thick paving, which is heavy and easily shifts, leaving a crooked cut.
3. Cutting: the blade is guided slowly along the line without forcing it. Wet cutting is ideal, as the water cools the blade and keeps the dust down.
4. Checking and finishing: the piece is tried in place and any sharp burrs are ground off.
5. Laying: the cut piece is bedded in, levelled with the blocks around it, and finally the whole area is compacted with a plate compactor and brushed with jointing sand.

In practice it pays to plan the layout so that no thin slivers are left at the edges. As a rule of thumb, an edge piece should be at least half the width of a full block. Small triangles and narrow strips are hard to lock in place, break under load and eventually work loose.

Four types of tool are used on concrete block paving. Each suits a slightly different situation.

• Angle grinder with a diamond blade for concrete: quick to grab and able to handle cuts in place and curves. It needs a steady hand, though. Edges chip more easily and dry cutting produces a lot of dust.
• Bench saw for paving with water cooling: gives a straight, clean cut and suits a larger number of straight cuts. The water greatly reduces dust.
• Petrol cut-off saw with a large blade: used mainly for thick paving and kerbs, where a smaller grinder cannot cut deep enough.
• Block splitter: it does not cut the block but snaps it. It is fast and dust-free, but the edge is rough. It suits places where a kerb, gravel or lawn hides the edge, not visible details.

Choose the blade to match the material. For concrete, use a concrete blade or a general-purpose construction blade; for natural stone, a blade for hard materials. A wrong or worn blade overheats, cuts crooked and tears the edges.

The thickness of paving depends on what will walk or drive over it. Paving 4 cm thick usually goes on paths and patios used by pedestrians only. Paving 6 cm thick is common around houses and, according to many manufacturers, can take an occasional car. Thicknesses of 8 cm are used on driveways and parking spaces, 10 cm where heavier vehicles drive. The manufacturer of the specific paving always states its intended use.

When cutting, the difference shows mainly in these points:

• Depth of cut: a larger angle grinder cuts through 4 to 6 cm paving in one pass. With 8 to 10 cm, you often have to cut from both sides or use a cut-off saw or bench saw with a bigger blade.
• Time and wear: a thicker block takes longer to cut, the blade heats up more and wears faster.
• Risk of breakage: when cutting from both sides, the two cuts must meet exactly. Otherwise a step is left, or the block snaps off at an angle when it is broken through.
• Weight: thick blocks are heavy, harder to hold steady and harder to handle when trying them in place.

On areas that carry vehicles, every badly cut edge also shows up more. A car pushes on the edge pieces as it drives over, and a small or poorly locked piece soon comes loose.

How much work the cutting takes depends less on the size of the area and more on how many details it has. A simple rectangular patio between straight kerbs only needs cutting on two sides. An area around a house with corners, inspection chambers, downpipes and a curved flower bed can need many times more edge cuts.

The job gets harder mainly with:

• Curves and angled joins, where every piece has a different shape
• Cut-outs around chambers, manhole covers, posts and downpipes
• Thicker or very hard paving, for example with crushed stone in the surface
• Paving with a surface finish or coloured top layer, where every chip is instantly visible
• Little space for cutting, or restrictions on dusty work because of neighbours

On the other hand, straight and properly set kerbs, a well planned pattern without thin slivers and room to wet-cut away from the paved area all make the job easier.

A common mistake is dry cutting right above the laid paving. Concrete dust mixed with water or dew forms a film on the surface that is hard to remove. The slurry from wet cutting also has to be rinsed off before it dries. Another mistake is setting a cut piece without levelling it with its neighbours. This leaves a lip that people trip over and that breaks off during compaction.

You can manage straight cuts on a patio or path in 4 to 6 cm paving yourself if you have experience with an angle grinder. For thick paving and complicated curves, it is safer to leave the work to a tradesperson with a bench saw. Concrete dust contains silica, which damages the lungs, so never skip protective equipment.

1. Put on safety glasses, an FFP2 or preferably FFP3 respirator, ear defenders, gloves and sturdy footwear.
2. Check that the grinder has its guard fitted and a diamond blade made for concrete, and that the blade is not damaged.
3. Hold the block in position and mark the cutting line along its full length with a pencil or marker.
4. Place the block on a firm surface away from the laid paving and secure it so it cannot move.
5. Cut slowly in several passes without forcing it, and let the blade work at its own speed.
6. Where possible, wet the cutting line with water to reduce dust and overheating.
7. If the grinder cannot reach the full depth, turn the block over and finish the cut from the other side exactly on the same line.
8. Try the piece in place and gently grind off any unevenness.
9. Bed the piece in, tap it level with its neighbours using a rubber mallet and rinse the dust off the surface.

When you accept the work, walk along the whole edge of the paved area and check these points:

• Cuts are straight or follow the curve smoothly without jagged steps
• Edges on the visible side are not chipped or cracked
• Edge pieces are not too small and sit firmly between their neighbours and the kerb
• The joint along the kerb or wall is even and filled with sand
• Cut pieces are level with the surrounding paving and leave no lip
• There are no large gaps around chambers and covers that are filled with sand alone
• The paving surface shows no dried traces of cutting dust or slurry
• Offcuts and waste are cleared from the paved area and its surroundings