How do I cut a brick or a block accurately?
Splitting cleanly with a bolster, cutting accurately with a disc, and the dust control that makes power cutting acceptable rather than dangerous.
- Difficulty
- intermediate
- Time
- 15 min
- Read
- 3 min
- Safety
- warning
Short answer
For a rough cut in soft brick, score all four faces with a bolster and a club hammer, then split it with one firm blow on the scored line. For an accurate cut or a hard brick, use a wet-cut diamond disc. Aerated blocks cut with an ordinary coarse hand saw and no dust at all.
Safety
What you'll need
- Eye protection and heavy gloves
- An FFP3 mask for any power cutting
- A brick bolster and a club hammer, for hand cutting
- A disc cutter or angle grinder with a diamond masonry disc and a water feed
- A hand saw or block saw for aerated blocks
- A pencil, a square and a firm surface such as sand or a bed of soil
Step by step
- Work out how accurate the cut has to be.A cut brick buried in a wall with only one face showing tolerates a rough split. A cut in a visible position, a cut that has to be square, or a cut through a hard engineering brick needs a disc.
- Mark the line on all faces.Square the line right round the brick with a pencil, using a try square or the edge of another brick. A cut marked on one face only will wander.
- Cut on a forgiving surface.Sand, soil or a bed of soft ground, not concrete. A hard surface reflects the blow back and shatters the brick unpredictably.
- Score before you split.With the bolster on the line and its flat face towards the piece you are keeping, work round all four faces with moderate blows, cutting a groove. Do not try to split it on the first hit.
- Split with one firm blow.Once the score is continuous, one decisive blow on the scored line on the widest face. Hesitant tapping crushes the brick rather than splitting it.
- Cut hard bricks with a disc.Engineering brick, dense block and many modern wirecuts will not split cleanly. Use a diamond masonry disc, cut a groove all round rather than trying to go through in one pass from one side, and then break the remaining web.
- Wet-cut or use extraction, without exception.Either a disc cutter with a water feed, or a water bottle and an assistant keeping the cut wet, or an on-tool extraction shroud connected to an M-class vacuum. Water suppression cuts the airborne dust by around nine tenths, and this is the difference between a routine job and a genuinely dangerous one.
- Cut outside and think about the neighbours.Silica dust does not stop at your boundary and it gets into open windows, washing and cars. Position yourself with the wind taking dust away from people, and warn anyone nearby.
- Saw aerated blocks.A coarse hand saw or a purpose-made block saw goes through an aerated block quickly and cleanly, with no cloud, no power tool and no grinder. There is no reason to use a disc on these.
- Clean up the cut.Dress rough edges with the side of the bolster or a brick hammer. On a visible cut, place the cut edge where it will be least seen and bed it carefully.
If it doesn't work
The brick shatters instead of splitting
Cause: Cut on a hard surface, hit too hard too early, or a brick with internal perforations — Fix: Cut on sand or soil, score all four faces properly first, and for perforated bricks use a disc rather than trying to split them.
The split runs away from the line
Cause: The scoring was incomplete or only on one face — Fix: Score right round the brick before splitting. On a hard brick, cut a deeper groove with a disc before breaking it.
The cut face is ragged and shows in the wall
Cause: Hand-split where the position needed a sawn cut — Fix: Cut visible bricks with a diamond disc, and orient any hand cuts so the split face is bedded and the good face shows.
Huge dust cloud despite a mask
Cause: Dry cutting — the mask filters what you breathe but does nothing about the exposure to everyone else, or about dust settling everywhere — Fix: Wet-cut or use on-tool extraction. Treat the mask as the last line of defence, not the control.