Sealing a drain pipe penetration through a concrete foundation is something many NZ homeowners can tackle themselves — but only if the drain pipework itself is already in place and you're simply filling the gap around it. If the work involves connecting, modifying, or extending any drain, waste, or stormwater pipe, that becomes restricted drainlaying work under NZ law and must be carried out by a licensed professional.
What Counts as Restricted Work?
In New Zealand, any work that involves connecting to, laying, altering, or repairing a drain (including underground stormwater and wastewater pipes) is restricted work under the Plumbers, Gasfitters and Drainlayers Act 2006. Only a licensed drainlayer can legally carry out this work. Getting it wrong can result in fines, failed inspections, and costly remediation.
If your pipe is already correctly installed and you simply need to seal the annular gap (the space between the pipe and the concrete), that sealing task alone is generally not restricted work — it's more of a waterproofing and weathertightness job.
Why Sealing This Gap Matters
Leaving an unsealed penetration can cause serious problems:
- Water ingress — groundwater, surface water, or stormwater can track along the pipe and enter your subfloor or basement.
- Pest entry — rats, mice, and insects can squeeze through surprisingly small gaps.
- Radon and soil gases — in some NZ regions, sealing penetrations helps limit gas entry.
- Structural moisture damage — ongoing dampness can degrade timber framing and affect your home's compliance with the NZ Building Code, particularly clauses E2 (External Moisture) and E3 (Internal Moisture) — though E3 primarily relates to internal wet areas such as bathrooms; the more directly relevant clause for subfloor and foundation moisture in this context is E2.
Do You Need a Building Consent?
For simply sealing an existing penetration gap, a building consent is generally not required — this typically falls under Schedule 1 exemptions. However, if the penetration itself is new, or if any structural concrete work is involved, you should confirm with your local council before starting. Rules vary by council and by the scope of work. Always check — don't assume.
Choosing the Right Sealant Product
The product you use matters a great deal. Concrete foundations are subject to ground movement, moisture, and in some cases hydrostatic pressure. Standard silicone or acrylic gap fillers are generally not suitable for below-ground or wet-area foundation penetrations.
Here are the main product types used by NZ tradespeople:
| Product Type | Best For | Example Brands |
|---|---|---|
| Hydraulic cement / quick-set plug | Active water leaks, wet concrete | Available at Bunnings, Mitre 10 |
| Polyurethane expanding foam (closed-cell) | Dry internal penetrations, pest exclusion | Available at Bunnings, Mitre 10 |
| Flexible polyurethane sealant | Movement-prone joints, above-ground | Sika Flex range |
| Cementitious waterproofing slurry | Damp-proofing around pipe entry | Ardex, Mapei |
| Pre-formed link seals / mechanical seals | Professional-grade, high-water-table sites | Specialist suppliers |
For most DIY situations with a dry, internal-facing penetration, a closed-cell expanding foam followed by a flexible polyurethane sealant bead over the top is a practical and effective approach. For any penetration that faces soil or is below ground level, a cementitious waterproofing product or hydraulic cement is a better choice.
Step-by-Step: Sealing a Dry Foundation Penetration
- Clean the gap — remove loose concrete, dust, old sealant, and any debris. A wire brush and vacuum work well.
- Check the pipe — make sure the pipe is undamaged and correctly supported. If it looks cracked or misaligned, call a licensed drainlayer before proceeding.
- Apply backer rod (if the gap is wide) — a foam backer rod gives the sealant something to bond against and controls depth.
- Fill with expanding foam or hydraulic cement — follow the manufacturer's instructions carefully. Don't overfill; foam expands significantly.
- Apply a sealant bead — once cured, run a bead of flexible polyurethane sealant around the pipe perimeter on both sides of the wall if accessible.
- Allow full cure time — don't expose to water until fully cured per the product datasheet.
Safety Notes
- Wear gloves and eye protection when working with expanding foam and polyurethane sealants — they bond to skin and are difficult to remove.
- Work in a ventilated area; fumes from some sealants can be irritating.
- If you're working in a confined subfloor space, review WorkSafe NZ guidance on confined space safety before entering.
- If you suspect asbestos in older concrete or pipe lagging (pre-1990s homes), do not disturb the material — get it tested first.
When to Call a Professional
You should engage a licensed drainlayer or builder if:
- The drain pipe itself needs to be moved, connected, or repaired.
- There is active water ingress or the foundation shows signs of cracking or structural movement.
- The penetration is below the water table or subject to hydrostatic pressure.
- You're unsure whether a building consent is required.
- The gap is large or irregular and you're not confident in the repair.
A qualified drainlayer can also ensure the work meets NZ Building Code requirements and won't cause issues at future LIM or building inspection. You can find licensed local drainlayers and builders on tradedirectory.co.nz.
Sources & Further Reading
- Plumbers, Gasfitters and Drainlayers Board — licensing and restricted work
- MBIE Building Performance — NZ Building Code and consents
- BRANZ — moisture and weathertightness guidance
- Sika NZ — sealant and waterproofing products
- Ardex NZ — cementitious waterproofing systems
- WorkSafe NZ — health and safety guidance
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