How to Cut a Clean Circle or Curve in Brickwork for a Pipe

Cutting a clean circle or curve in brickwork for a pipe — whether it's for a dryer vent, flue, or drainage pipe — is achievable for a confident DIYer with the right tools and a careful approach. Rushing the job or using the wrong equipment is the most common cause of cracked or crumbling brickwork, so patience is key.

Understand What You're Cutting Through

Before you start, identify what's in the wall. Standard NZ clay or concrete bricks are hard and brittle, and mortar joints behave differently again. More importantly, never cut into a wall without checking for hidden services — electrical cables, water pipes, and gas lines can all run through or behind brickwork. Use a cable and pipe detector (available from Bunnings or Mitre 10) before picking up any cutting tool.

Also consider whether the wall is load-bearing. Removing brick from a structural wall without proper support can be dangerous and may require a building consent. If you're unsure, check with your local council or consult a Licensed Building Practitioner before proceeding.

Tools You'll Need

For a clean circular cut in brick, you have a few options depending on the hole size:

• Core drill with a diamond-tipped core bit — the best tool for the job. Produces a clean, round hole with minimal cracking. Available to hire from most tool hire shops.
• Angle grinder with a diamond blade — useful for scoring and cutting curves, but requires more skill to keep lines clean.
• SDS rotary hammer drill with a masonry bit — used to drill a series of holes around the perimeter before chiselling out the waste (the "dot and knock" method).
• Cold chisel and club hammer — for breaking out waste material after drilling.
• Masonry chisel — for tidying up edges.

For most pipe penetrations (say, 100–150 mm diameter), a hired core drill is the cleanest and fastest solution. Larger holes may need to be cut in sections.

Step-by-Step: Core Drilling Method

This is the recommended approach for a neat, professional result.

1. Mark the centre point of your hole on the brick using a pencil or chalk. Try to position the hole so it passes through as few mortar joints as possible — mortar is softer and can crumble unevenly.
2. Select the correct core bit size — choose a bit slightly larger than your pipe's outside diameter to allow for a sleeve or sealant. Check the pipe manufacturer's specs.
3. Set up your core drill with water cooling if the bit requires it (wet-core bits need a water feed to prevent overheating and dust).
4. Drill slowly and steadily, applying firm, even pressure. Let the diamond bit do the work — don't force it.
5. Work from both sides if the wall is thick (over about 200 mm). Drill halfway through from one face, then complete the hole from the other side to avoid blowout on the back face.
6. Remove the core plug — it may come out whole or in pieces. Use a chisel to free it if needed.
7. Clean up the edges with a masonry chisel and brush away dust.

The "Dot and Knock" Method (No Core Drill)

If you don't have access to a core drill, you can achieve a reasonable result using a rotary hammer drill and chisel:

1. Draw your circle on the brick face using a template (a tin lid or offcut pipe works well).
2. Drill a series of closely spaced holes (around 10–15 mm apart) around the inside edge of the circle using a masonry bit.
3. Connect the holes by carefully chiselling between them with a cold chisel and club hammer.
4. Work inward gradually, removing small pieces at a time.
5. Tidy the edges with a masonry chisel — expect the result to be rougher than a core-drilled hole, but it can be made good with mortar or a pipe collar.

Finishing the Penetration

Once your hole is cut, the pipe should fit through with a small gap around it. Fill this gap correctly:

• Use a pipe collar or escutcheon plate on the external face for a neat finish.
• Seal around the pipe with a flexible, weatherproof sealant suitable for masonry — products from Sika are commonly used in NZ for this purpose.
• If the penetration is external, ensure water cannot track back into the wall cavity. This is particularly important under the NZ Building Code Clause E2 (External Moisture) — water ingress around pipe penetrations is a common cause of moisture damage.
• Make good any cracked or damaged mortar joints around the hole using a matching mortar mix.

Safety First

Cutting masonry produces fine silica dust, which is a serious health hazard. Always wear a properly fitted P2 respirator (not just a dust mask), safety glasses, hearing protection, and gloves. Work in a ventilated area and consider wet-cutting to suppress dust. For guidance on silica dust risks, refer to WorkSafe NZ.

When to Call a Professional

Some situations require a licensed tradesperson — don't attempt these yourself:

• Plumbing and drainlaying penetrations (e.g., for drain pipes or water supply) may involve restricted work under the Plumbers, Gasfitters, and Drainlayers Act. Check with the Plumbers Gasfitters & Drainlayers Board.
• Gas flue or appliance penetrations must be carried out or certified by a licensed gasfitter.
• Electrical conduit penetrations through walls must comply with the Electrical Wiring Regulations — consult the Electrical Workers Registration Board if in doubt.
• Load-bearing or structural walls — always get professional advice before cutting.
• If you're not confident with the tools or the wall construction, a qualified bricklayer will get the job done cleanly and safely. You can find experienced local bricklayers on tradedirectory.co.nz.

Sources & Further Reading

• MBIE Building Performance – NZ Building Code
• WorkSafe NZ – Silica Dust
• Plumbers Gasfitters & Drainlayers Board
• Licensed Building Practitioners
• Sika NZ – Sealants & Adhesives
• BRANZ – Building Research