Cutting a new sink opening into an existing benchtop is a job many confident DIYers can tackle — but it's not without risk. Get it right and you'll save on labour costs; get it wrong and you could crack a stone benchtop, chip a laminate edge, or end up with a gap that lets water into your cabinetry. Here's what you need to know before you pick up a jigsaw.
What Benchtop Material Do You Have?
The material your benchtop is made from is the single biggest factor in whether this is a realistic DIY project.
- Laminate (Formica-style) over particleboard or MDF — the most DIY-friendly option. A sharp jigsaw with a fine-tooth blade will do the job cleanly if you work carefully.
- Solid timber or engineered timber — manageable with the right blade and a steady hand, but splintering is a risk on the top face.
- Acrylic solid surface (e.g. Corian-style) — cuttable with a jigsaw, but requires specific blades and careful technique to avoid cracking or melting the material.
- Engineered stone (Caesar stone, Silestone, etc.) or natural stone (granite, marble) — these should almost always be left to a professional. Stone requires diamond-tipped angle grinder blades or a wet saw, generates fine silica dust (a serious health hazard), and cracks easily if the cut isn't perfectly supported. Do not attempt stone without proper equipment and training.
- Porcelain or ceramic tile benchtops — specialist work; leave it to a tiler or cabinet maker.
Tools and Materials You'll Need
For laminate or timber benchtops, gather the following before you start:
| Item | Notes |
|---|---|
| Jigsaw | Variable speed; use a fine-tooth downstroke blade to reduce chipping |
| Drill with hole-saw or spade bit | To create a starter hole inside the cut line |
| Tape measure and pencil | For accurate marking |
| Masking tape | Apply over the cut line to reduce laminate chipping |
| Straight edge or template | Many sinks come with a paper template — use it |
| Clamps or a helper | To support the offcut so it doesn't drop and tear the laminate |
| Laminate edging or silicone sealant | To seal the exposed cut edge |
| Safety glasses and hearing protection | Non-negotiable |
Step-by-Step: Cutting the Sink Opening
1. Check your sink template
Most new sinks include a paper or cardboard template. If yours doesn't, measure the sink's rim carefully and draw the cutout yourself — the opening is typically 10–15 mm smaller than the outer rim on each side, but always follow the manufacturer's instructions.
2. Mark and tape the cut line
Apply masking tape over the area where you'll cut. Draw your cut line on top of the tape. This protects the laminate surface from the jigsaw foot scratching it and helps reduce chipping.
3. Drill your starter hole
Inside the cut line (not on it), drill a hole large enough to fit your jigsaw blade — typically 10–12 mm diameter. Stay at least 10 mm inside the line.
4. Make the cut
Insert the jigsaw blade into the starter hole and cut along the inside of your marked line. Keep the speed steady and let the blade do the work — don't force it. Have a helper support the offcut from below as you near the end of the cut, so it doesn't drop and tear the laminate.
5. Seal the exposed edge
Particleboard and MDF are extremely vulnerable to moisture. Once cut, immediately seal the raw edge with a waterproof silicone sealant or a purpose-made laminate edge sealer. This step is critical — skipping it is one of the most common causes of benchtop swelling and failure around kitchen sinks.
6. Test-fit and install the sink
Drop the sink in to check the fit before applying any sealant. Once happy, follow the sink manufacturer's instructions for clips and sealant. Run a continuous bead of neutral-cure silicone (not acetoxy/acidic cure) around the rim before lowering the sink into place.
Plumbing Connections — What You Can and Can't Do
Once the sink is in, you'll need to connect the water supply and waste. In New Zealand, plumbing work is restricted work under the Plumbers, Gasfitters and Drainlayers Act 2006. Connecting or altering water supply pipes and drain connections must be carried out by a licensed tradesperson registered with the Plumbers, Gasfitters and Drainlayers Board.
As a homeowner, you may generally do minor maintenance (such as replacing a washer or unblocking a trap) but connecting new supply lines or waste pipes to the existing system is a job for a licensed plumber. Always check with your local council if you're unsure what's permitted.
Do You Need a Building Consent?
Replacing or modifying a benchtop sink cutout is generally considered maintenance or repair work and is typically exempt from building consent under Schedule 1 of the Building Act 2004. However, if you're making significant changes to your kitchen layout or plumbing configuration, consent may be required. Always confirm with your local council before starting work — MBIE Building Performance has useful guidance on what's exempt.
When to Call a Professional
Call a qualified cabinet maker or kitchen installer if:
- Your benchtop is stone, engineered stone, or tile
- You're not confident with power tools or measuring accurately
- The existing benchtop is in poor condition or has previous water damage
- You want a seamless, warranty-backed result
- The sink position is changing significantly, requiring new cabinetry modifications
Silica dust from cutting stone is a recognised health hazard regulated by WorkSafe NZ — professional tradespeople have the right equipment and training to manage this safely.
You can find experienced local cabinet makers and kitchen specialists on tradedirectory.co.nz.
