Cutting block paving 80 to 100 mm thick

Block thickness is chosen by load. An 80 mm block is usually used for driveways and parking for cars, and 100 mm where heavier traffic is expected or where wheels often turn on the spot. If you are ordering cutting at this thickness, you almost always have a surface that takes vehicles. That changes how the cut is judged. It is not only about how the edge looks, but whether the cut piece can take the pressure of a tyre.

A thick block has a larger cut face. At 100 mm, the disc goes through almost twice as much concrete as on a 50 mm block. The cut takes longer, the disc heats up and wears faster, and there is more slurry and dust. A standard 230 mm angle grinder cuts roughly 60 to 70 mm deep, so it will not go through an 80 mm block in one pass. That is why this thickness needs different tools or a different method.

How the work is measured

The price list gives cutting in linear metres. As a rule, the length of the line along which the paving is cut is measured, for example the length of edging kerb where blocks have been cut in. Angled cuts, curves and cut-outs around gullies or posts mean more cuts per metre and more effort. Agree in advance with the contractor how these spots will be measured, so the final bill does not lead to an argument.

Cutting is not a separate job left until the end. It runs alongside laying, or straight after it, before the joints are filled and the surface is compacted with a plate compactor.

Marking the cut

The paver lays full blocks right up to the edge, that is the kerb, the wall or the gully, so they overhang it. Each block is then marked with a pencil, chalk or a string line. When marking, the joint left between the cut piece and the kerb has to be taken off, usually about 3 to 5 mm. The block must not be jammed tight against the kerb, or compaction will push it up or chip its edge.

Cutting on a bench saw or in place

There are two common methods, and on larger jobs they are often combined.

• Bench saw: each block is lifted, cut on a water-cooled saw and put back. The cut is accurate and square and the paving stays clean, but the work is slower because every piece is handled twice
• Cutting in place: full blocks are laid over the edge, a string line is set and the whole row is cut in one go with a petrol cut-off saw. The line is straight and the work is fast, but slurry runs over the laid paving and must be washed off at once. Care is also needed not to cut into the kerb with the disc

With 80 to 100 mm paving, cutting in place is usually done in two stages: first a cut from the top to the depth the machine handles safely, then the piece is lifted and finished off. The alternative is a saw with a larger disc that goes through the full thickness.

Bedding the cut pieces and cleaning up

The cut pieces go back in place, are tapped down with a rubber mallet level with the surrounding blocks, and the joint widths are checked. Slurry and dust are washed off the surface with water while still wet. Only then are the joints filled with sand and the area compacted with a plate compactor fitted with a rubber mat.

How long it takes

Time depends mainly on the number of cuts per linear metre. A straight line along a kerb, with paving laid square to the edge, goes fairly quickly. A herringbone pattern at 45 degrees, curves and many cut-outs around obstacles can make the same length take several times as long. With thick paving you also have to allow for changing or cooling the disc and for cleaning the surface more often.

Water-cooled bench saw

For accurate cuts that will be on show, a masonry bench saw with a diamond blade, usually 350 mm or larger, is used. The block sits on a sliding table, water cools the blade and the cut is smooth and square. For a 100 mm block you need a saw with enough cutting depth. Smaller site saws sometimes lack it, and the block then has to be turned over.

Petrol or electric cut-off saw

A handheld cut-off saw with a 300 to 400 mm disc is the usual paver's tool for cutting in place. On UK sites it is often just called a "Stihl saw", whatever the make. With a 350 mm disc it will usually go through a 100 mm block if you cut slowly and with water. It is heavy, loud and needs experience. If it is guided badly, the disc can bind and the saw kicks back.

Angle grinder

A large angle grinder is useful for small trims, shaping curves and cut-outs around manhole covers. It will not cut the full 80 to 100 mm in one pass, though. You have to cut from both sides, and the two cuts must meet exactly, otherwise you get a step on the cut face.

Block splitter

For thinner paving, a block splitter (guillotine) is a quick option. At 80 to 100 mm you need a heavy hydraulic or lever splitter, and the break is still uneven, with a ragged underside. It is therefore not used for cuts at the kerbs of a driveway, at most for roughly shortening pieces that are then cut properly.

Discs

Concrete paving is cut with a segmented diamond disc made for concrete. With paving containing hard aggregate, such as exposed-aggregate or granite-faced blocks, the disc wears faster and should be one rated for hard materials. A blunt disc cuts slowly, overheats, burns the block edge and raises the risk of a segment coming loose.

The price list also has a separate item for cutting block paving 40 to 60 mm thick. At first glance it is the same job, but in practice the two variants differ quite a lot.

• Use: 40 to 60 mm paving belongs on paths, patios and areas for foot traffic. 80 to 100 mm paving is for areas cars drive onto. If you have a driveway to a garage, this is usually the item you need
• Tools: thinner paving can be cut by a large angle grinder in one pass and can also be split. Thick paving needs a saw with a bigger disc or cutting from both sides
• Time per metre: a cut through a 100 mm block takes noticeably longer, the disc wears more and there is more slurry
• Demands on the cut piece: on a path a small piece holds, but under a car wheel a narrow sliver comes loose, breaks or tips. With thick paving the minimum size of a cut piece is watched much more strictly
• Safety: larger machines mean more risk of kickback, more noise and more dust, so the work needs a more experienced operative
• Weight: a 100 mm block is heavy, and repeatedly lifting pieces to the bench saw and back is physically harder

If both thicknesses meet on one job, for example a path to the front door and a driveway to the gate, cutting is usually priced by the thickness in each section. The two should be separated by an edging kerb so the thin paving does not take vehicle loads.

Length of cut is not the only thing that decides how demanding the work is. Two areas with the same number of linear metres can need very different effort.

Easier

• Straight kerbs and right-angled shapes
• A laying pattern square or parallel to the edge, so only one row is cut
• Area dimensions planned around the block module, so the edge pieces come out as large as possible
• Free access for the saw, plus water and power on site
• Standard concrete blocks without hard aggregate on the face

Harder

• Herringbone or angled laying, where every edge block is a diagonal cut
• Curves, radius kerbs and rounded corners
• Lots of obstacles: gullies, manholes, covers, gate posts, channel drains, steps
• Exposed-aggregate, granite-faced or heavily textured blocks, which wear discs quickly and are hard to clean of slurry
• Cutting next to a finished render, fence or window that has to be protected from slurry and dust
• Noise limits in a residential area. Local councils often have their own rules on working hours for noisy work, so it is worth checking

Cutting sits between preparing the base and final compaction. If something before it is not finished, cuts have to be redone or end up inaccurate.

• Edging kerbs must be bedded in concrete and set hard, otherwise they move during compaction and the joint at the cut pieces opens up
• Gullies, manholes and covers must be set at their final level. A cut-out around a cover that is raised afterwards no longer fits
• Channel drains in front of the garage should be installed before laying, so blocks can be cut to their edge
• If cables are planned for a gate, lighting or a car charger, ducts should be laid in the base beforehand. Cutting open a finished surface for a cable means more cuts and replaced blocks, and the electrical connection itself must be done only by a qualified electrician
• Cutting is followed by filling the joints and compaction. The plate compactor should only go over the area once all cut pieces are in place, otherwise the edge pieces will not settle the same way as the rest

Cutting paving in itself does not need any permission. If you are building the area from scratch, for example a new driveway or a new access from the road, check your local building regulations with the local authority. Rules on surface water drainage for front gardens and driveways often apply, and a new or widened access across a pavement usually needs the agreement of the highway authority. In a block of flats, agree any work on shared areas with the building management or owners' association.

Narrow slivers at the edge

The most common mistake on vehicle paving. A cut piece only a few centimetres wide has no support from its neighbours, so under a wheel it tips, cracks or loses a corner. A rule of thumb from practice is not to leave pieces smaller than roughly a third to a half of a full block. If a small cut would come out, the second-to-last row is shifted, or two larger pieces are cut instead of one small one.

Filling a large gap with mortar

When a cut piece is too short, the gap at the kerb is sometimes filled with concrete or mortar. This infill cracks, frost breaks it up, and after a few winters there is a hole at the edge.

An angled or ragged cut

When two cuts from opposite sides do not meet, or when the rest of an incomplete cut is snapped off, a lip forms on the underside of the block. The block then does not sit on its bed with its full area, so it rocks and creaks or knocks when you drive over it.

Slurry left on the surface

Cement slurry that dries on the paving leaves grey stains and haze. It shows badly on coloured and exposed-aggregate blocks and is hard to remove later, often only with a cement residue cleaner. The fix is simple: wash it off straight away while it is wet.

Pieces jammed in without a joint

A cut piece pressed tight against the kerb or the next block has no room to move. During compaction or the first frosts, its edge chips off.

Dry cutting

Concrete contains quartz, and the fine dust from cutting contains respirable crystalline silica, which is harmful to health. Health and safety rules in many countries require dust control for this reason. Dry cutting without extraction also covers the whole surroundings in dust, including windows and the neighbours' cars. Water binds the dust and cools the disc.

If you are laying the paving yourself, you can manage the cutting too, but at 80 to 100 mm you will be working with a heavy machine. You can hire a large water-cooled bench saw from a tool hire shop. A handheld cut-off saw is better left to someone with experience of using one. Do not cut a single block without protective equipment.

1. Get protective equipment ready: safety glasses or a visor, ear defenders, an FFP3 respirator, tough gloves and steel toe-cap boots.
2. Set the saw on a firm, level surface away from the laid paving, connect the water and check the blade is made for concrete and is undamaged.
3. Lay full blocks up to the edge so they overhang the kerb.
4. Mark the cut line on each block and take off a joint of about 3 to 5 mm.
5. Check the cut piece will not come out too narrow, and shift the second-to-last row if needed.
6. Number the block, lift it and place it on the saw table so it sits flat on its full face.
7. Cut slowly and evenly without forcing the blade, and let the saw do the work.
8. Check the cut is square and has no lip on the underside.
9. Rinse the slurry off the piece and put it back in its place.
10. Tap it down with a rubber mallet level with the surrounding blocks.
11. Wash slurry and dust off the laid surface while still wet.
12. Once all cut pieces are in, fill the joints and compact the area with a plate compactor fitted with a rubber mat.

Do not pour slurry water into a surface water drain or a flower bed. Let it settle in a container and dispose of the sediment as construction waste.

Check the cut pieces before and after compaction. Once the joints are filled, some faults are harder to see.

• The line of cuts along the kerb is straight and follows its shape, including on curves
• The joint between cut pieces and kerb is even, with no block jammed tight anywhere
• There are no narrow slivers at the edges and no pieces clearly smaller than agreed
• Gaps at the edge are not filled with mortar instead of block
• Cut faces are square, with no ragged underside and no chipped edges
• Cut-outs around gullies, manholes and covers are tight, and water runs to the gully
• Cut pieces do not rock after compaction and sit flush with the surrounding paving
• There are no dried slurry stains on the surface
• The surroundings are clean, and offcuts and slurry have been taken away
• The length of cuts in linear metres is agreed, including how curves and cut-outs are measured