Yes, you can absolutely use a router to create a bullnose edge on decking boards, and it's a popular way to give your deck a polished, professional look. A bullnose profile — a smooth, rounded-over edge — softens the sharp corners of your decking, reduces splinter risk, and adds a tidy finish to exposed board ends and outer edges. With the right router bit, a steady hand, and a few precautions, this is a manageable DIY task for a confident homeowner.
What You'll Need
Before you start, gather the following:
- Router — a fixed-base or plunge router both work; a fixed-base is generally easier for edge profiling
- Roundover router bit — typically a 6 mm or 10 mm radius roundover bit creates a classic bullnose look; for a full bullnose (both edges rounded to meet), you'll rout both the top and bottom faces
- Router table or edge guide — a router table gives the most consistent results, especially for long runs of boards
- Hearing protection, safety glasses, and dust mask — hardwood and treated timber dust can be hazardous
- Clamps and a stable workbench
- Sandpaper (120–180 grit) for finishing after routing
Choosing the Right Router Bit
For a bullnose profile, you want a roundover bit with a bearing guide. The bearing rides along the face of the board and controls the depth of cut automatically, giving you a consistent profile along the full length.
- A 6 mm radius roundover bit gives a subtle, gentle curve — good for thinner decking (around 90 mm × 19 mm)
- A 10 mm radius roundover bit suits thicker boards (e.g., 90 mm × 45 mm) and creates a more pronounced bullnose
- For a full bullnose, rout the top edge first, flip the board, and rout the bottom edge with the same bit and depth setting
Carbide-tipped bits are worth the extra cost — they stay sharp far longer, especially in hardwoods like kwila (merbau) or treated pine. You'll find a good range at Bunnings or Mitre 10.
Timber Considerations for NZ Decking
The type of timber you're working with makes a difference to your approach:
| Timber Type | Routing Notes |
|---|---|
| Treated pine (H3.2 / H4) | Routes easily; watch for resin pockets; wear a dust mask as treated timber dust requires care |
| Kwila (merbau) | Dense hardwood; use sharp carbide bits and take lighter passes; can bleed red tannins |
| Vitex | Works well with routers; relatively stable grain |
| Composite decking | Check manufacturer guidelines — some composites can be routed, others cannot without voiding warranty |
For treated timber, always check the treatment level. Decking in ground contact or near water typically requires H4 or H5 treatment. Refer to BRANZ guidance on timber durability and treatment for NZ conditions.
Step-by-Step: Routing a Bullnose Edge
- Set up safely — secure the board firmly with clamps. Never rout a board that can move.
- Set your bit depth — do a test pass on a scrap piece of the same timber first. Adjust until you're happy with the profile.
- Rout with the grain where possible — on end grain, take very light passes to avoid tear-out.
- Feed direction matters — when hand-routing, move the router from left to right (against the bit rotation) to maintain control. On a router table, feed the timber from right to left.
- Take light passes on hardwoods — don't try to achieve the full profile in one pass on dense timbers.
- Sand the routed edge — finish with 120 then 180 grit sandpaper to smooth any minor marks left by the bit.
- Apply your finish promptly — a freshly routed edge will absorb stain or oil well. Products from Resene or Wattyl offer good NZ-specific decking oils and stains suited to our UV and moisture conditions.
Safety Notes
Router safety is important. Routers spin at very high RPM and can cause serious injury if the workpiece moves or the bit catches. Always:
- Wear eye and hearing protection and a P2 dust mask
- Keep hands well clear of the bit
- Unplug the router before changing bits
- Check that the bit is fully seated and the collet is tight before starting
- Be aware that treated timber dust may contain preservative chemicals — refer to WorkSafe NZ guidance on working safely with treated timber
Does This Require a Building Consent?
Routing decking boards is a finishing task and does not require a building consent on its own. However, if you're building a new deck, consent requirements depend on the deck's height, size, and proximity to boundaries. Decks over 1.5 m above ground generally require consent. Always confirm with your local council, as Schedule 1 exemptions under the Building Act can vary. See MBIE Building Performance for general guidance.
When to Call a Professional
Routing bullnose edges is DIY-friendly, but there are times when it's worth bringing in a qualified deck builder:
- You're working with a large volume of boards and want a fast, consistent result using a router table setup
- You're unsure about the structural build of the deck itself — framing, fixing, and joist spacing should comply with NZS 3604 and relevant building consent conditions
- The decking timber is unfamiliar or particularly hard and you're not confident with the router
- You want the whole deck built and finished to a high standard
A skilled deck builder will have the tools and experience to knock out bullnose edges efficiently and ensure the whole project meets the NZ Building Code. You can find qualified local deck builders on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
