Quick answer
A slow leak under a kitchen sink shows in five ways, roughly in this order: a dark line along the back of the base floor, silicone lifting at the rim, a cupped shelf, a kick that gives underfoot, and a damp, earthy smell. Caught at the first tell it is a plumber's callout; at the fourth, the base is gone and the benchtop has to come off. Melteca is why it gets caught late: the melamine face shrugs off liquid for hours, while Laminex's data sheet says the substrate underneath must never touch any liquid. A dry paper towel along the back corners, once a month, is the whole defence.
Key points
- The sink base is the only cabinet with plumbing in it, and the one every other cabinet is scribed to.
- Laminex tests the Melteca face against liquid agents for sixteen hours with no marks, then says the substrate must not touch liquid.
- Water enters at cut edges and drilled holes, so the board rots behind a surface that looks new.
- Gradual damage is a standard exclusion in NZ house policies, and the courts read sudden as minutes or hours, not weeks.
- A thirty-second check with a torch and a paper towel is the whole prevention programme, and a tenant can do it.
Four of the five stages happen where nobody looks.
A property manager rings about a unit in Papakura. The tenant mentioned in passing that the kitchen smells a bit. Nobody is worried: no puddle, no drip, the tap works, the door shuts as it always has. Six weeks later the kick gives way under a vacuum cleaner and the whole base comes out — and the benchtop with it.
This is about the slow ones. A burst flexi hose announces itself, and your insurer will call it sudden. The leak that costs real money weeps millilitres an hour off a compression fitting, a waste seal or a dishwasher tail, down the back of the cabinet where nothing is stored. It does that for a year, and in a rental nobody has a reason to look.
Why the sink base is the cabinet you cannot afford to lose
Every other cabinet in the run is a box. The sink base is a box with services in it: hot and cold tails, a waste, a trap, nearly always a dishwasher hose. It is the only cabinet where a fitting can weep for months untouched, because the space behind the bin is dead storage.
It is also the datum. The joiner levels it first and scribes the neighbouring gables to it, because the cutout has to land where the waste is. Pull it out later and you are unpicking the run. The top has to lift: laminate rarely survives that, stone means a templater and a second visit. The cabinet was never the expensive part — the benchtop decision sets the price of every repair beneath it.
Melteca is exactly why you catch it late
Laminex's technical data sheet for Melteca is unusually honest, and both halves sit on one page. Resistance to staining: liquid agents, sixteen hours, no visible marks. Steam resistance: two hours, no cracks or blisters. Then, in Limitations: “The Melteca substrate must not come in contact with any liquid. Failure to keep dry will affect the performance of the panel.”
That is the failure mode. The face is cured melamine and does not care about water; the core is particleboard or MDF and cares enormously. Water never enters through the bit you are looking at. It enters at the edges: the holes cut through the base floor and back panel for the waste and the tails, anywhere the board was cut on site and not resealed. Hence the sheet's other line — any exposed substrate must be sealed before service.
Raw board would tell you straight away: unfinished MDF darkens and furs within days and somebody sees it. Melteca gives no warning, which is why it is still right for a rental and why it needs a check raw board does not. How melteca is put together is worth ten minutes.
| Part of the panel | Tested how | Result | What that means under your sink |
|---|---|---|---|
| Melamine face — staining | Liquid agents, 16 hours | No visible marks | The surface looks fine long after the leak started |
| Melamine face — steam | Steam, 2 hours | No cracks or blisters | A dishwasher vent will not mark the door front |
| Melamine face — dry heat | 180°C for 20 minutes | No cracks | Not the failure you are hunting for |
| Substrate — liquid contact | Not in the performance table; prohibited under Limitations | “Must not come in contact with any liquid” | This is where the cabinet actually dies |
| Substrate — fungal decay | Panel moisture content | Resistant while moisture content stays at or under 18% | Above that, the smell is the decay, not the water |
The five tells, in the order they turn up
Owners and tenants both look for a puddle. There is almost never a puddle, because the board drinks it. The order is the useful part: see the fourth tell and the first three happened months ago.
| Tell | What you would notice | Usually means | Still savable? |
|---|---|---|---|
| Dark line at the back of the base | A shadow along the rear edge of the base floor, often only under torchlight | Water is tracking, but the board is still hard | Yes — a plumber and a dry-out |
| Silicone lifting at the rim | The bead around the sink has parted, gone chalky, or grown a black line | The seal has failed and the cutout edge is drinking from above | Yes — reseal, if the cutout edge is sound |
| A shelf that has cupped | The shelf no longer sits flat; a straightedge rocks on it | The board has swelled and will not come back | Partly — shelf out, base inspected |
| A kick that gives underfoot | The kickboard flexes or crumbles when you press it with a foot | Water reached the floor of the cabinet and sat there | Rarely — usually a new base |
| The smell | Damp and earthy, strongest in the first second after the door opens | Decay in the board, not on it | No — moisture content has been over 18% long enough to start |
A dark line at the back of the base
Get a torch and get your head in there. The back edge of the base floor, where it meets the back panel, is the lowest flattest part of the cabinet and where a weeping fitting drains to. Early it is a shadow, not a stain. Thumbnail test: sound board resists, wet board keeps the dent.
Silicone lifting at the rim
The bead around a drop-in sink is the only thing stopping water on the bench reaching the raw cut edge of the cutout. When it parts, chalks or blackens it has stopped working, and that edge drinks every time somebody rinses a pot. Cheapest of the five to fix, most reliably ignored.
A shelf that has cupped
Melteca shelves leave the workshop dead flat. A shelf that takes moisture from one face swells and curls away from it. Lay a straightedge across it: rock means swell, and swell means the humidity in that cabinet has been high for a long time. A leak, or a cupboard that never dries out.
A kick that gives underfoot
A soft kick means you are not catching anything early. Water has pooled on the cabinet floor and sat behind it long enough to destroy it from the hidden side. The kick goes last because it is furthest from the leak — a rear-view mirror. Push it with a foot anyway: it is the one tell nobody has to crouch for.
The smell
Damp board smells like a garden shed, strongest in the first second after the door opens, before your nose adjusts. That is why the person living there stops noticing inside a fortnight and you clock it walking in. Tenants are not being difficult — their nose stopped telling them.
Nine times out of ten the tenant mentioned the smell to somebody. It just never got written down as a job.
The thirty-second check you can ask a tenant to do
None of this needs a trade or a tool. A phone torch and a dry paper towel, less time than boiling a jug. You can inspect no more than once every four weeks and must give 48 hours' notice — a tenant with a paper towel covers the gaps.
- Breathe in on the first second the door opens. Damp and earthy is a tell; bin smell is not.
- Torch the back edge where the base floor meets the back panel. Look for a tone change, not a puddle.
- Run a dry paper towel along both back corners. Wet towel on a dry day, ring someone.
- Press that back edge with a thumbnail. A dent that stays means the board has gone.
- Push the kickboard with a foot, and check the silicone at the rim while you are down there.
- Photograph the corner from the same angle every time. Six photos over six months is a diagnosis.
Across a portfolio this becomes a data problem, not a memory problem. A maintenance programme that actually catches things beats a property manager's recall, because four of the five tells are invisible unless somebody looks on purpose.
What it costs you to leave it
There is no honest single number: the price is set by what the water reaches, not how long it ran. The shape is dependable though, and it is not a slope. It steps, and each step is another trade who has to turn up. At a year the cabinets either side are suspect, nothing scribes true, and you are pricing a kitchen — entry grade sits in the lower five figures plus GST, before flooring.
Every month you wait adds another trade to the job.
Your insurer is not coming to the rescue
Landlords get this wrong, and precision matters. Gradual damage is a standard exclusion in New Zealand house policies. The Insurance Council's guide explains why: our courts have given “sudden” a specific legal meaning, and to be sudden, damage has to be abrupt, all at once, or instantaneous — minutes or hours, not days or weeks.
The trap is the gap between the damage and the discovery. You might find the swollen base suddenly; that does not make the damage sudden. The guide is explicit that what counts is when the damage occurred, and works through a case where the Ombudsman found a leak running four to five days was already gradual. Four to five days. Your sink base has been wet since winter.
Some policies carry a hidden gradual damage extension: a small capped benefit, generally limited to hidden damage from an internal water or waste pipe. Locating the leak falls on you where it is not covered. If your insurer declines, complain first; unresolved after two months it goes to the IFSO or FSCL. A process, not a plan.
What goes wrong
None of these are mistakes anybody would call careless. They are the ordinary ways a slow leak reaches month twelve.
- The tenant mentions the smell in a text about something else. Tenancy Services is blunt that tenants must report a needed repair straight away — but told and recorded are not the same thing.
- The inspection looks at the cupboard door, not inside it. The door is Melteca; it will look perfect for the entire life of the leak.
- Somebody replaces the swollen kick and calls it done. The kick was the symptom; the base floor above it is still wet.
- A new tap goes in and the site-drilled hole gets no sealer. Seal before service applies to every hole cut after the kitchen leaves the workshop.
- The rangehood recirculates, so every boil-up puts moisture straight back into the room.
Two deserve their own reading. The rangehood one is a compliance question as much as a joinery one: the kitchen ventilation rules landlords must meet are specific about extraction to the outside. The kick one leads to the most expensive mistake on the list — new fronts on a wet carcass is money set on fire, and the comparison between new doors and a new kitchen starts with whether the boxes are dry.
What to ask before you sign
Replacing a sink base, or specifying a kitchen you would rather not revisit in three years? These are the questions that decide it. What a kitchen warranty actually covers usually turns on whether the product was used and maintained as the manufacturer said.
- What substrate is the sink base, in writing? MR is worth specifying even though it is not waterproof.
- Are the cutout, the tap holes and the underside of the base floor sealed, and with what? Edgetape covers edges, not holes.
- If a fitting weeps, where does the water go? A base floor that pools it behind the bin is designed to hide it.
- Who seals the sink rim, joiner or plumber? This falls between trades more than any other detail.
- If the base comes out in five years, does the benchtop survive it? Ask before you choose the top.
- Is the extraction ducted outside, and does it meet the ventilation standard: for fans installed after 1 July 2019, a minimum 150mm diameter including ducting, or an exhaust capacity of at least 50 litres per second?
Frequently asked questions
Is water damage under a kitchen sink covered by house insurance in New Zealand?
Usually not, if the leak was slow. Gradual damage is a standard exclusion in New Zealand house policies, and the Insurance Council's guide explains that our courts read “sudden” as abrupt or instantaneous — minutes or hours, not days or weeks. What matters is when the damage occurred, not when you found it, so discovering a swollen base suddenly does not make it sudden. Some policies add a small capped benefit for hidden gradual damage from an internal pipe.
How do I tell if the swelling under my sink is old or still spreading?
Swelling does not reverse: once particleboard or MDF has taken on water and expanded, drying it leaves it swollen, so the swell says nothing about whether water is still arriving. Test for current moisture instead — run a dry paper towel along the back corners on a quiet day, and press the back edge with a thumbnail. A damp towel, or a dent that stays, means it is live.
Can I replace just the sink base cabinet, or does the whole kitchen have to go?
You can nearly always replace one cabinet; the question is what it takes with it. The benchtop has to lift to get a sink base out, and a laminate top often does not survive that, so the real scope is base plus top plus resealing. Matching is the other constraint: a new carcass is fine because nobody sees it, but a new door in a discontinued decor will not match.
Can I charge my tenant for water damage under the kitchen sink?
Probably not for the leak itself, because a fitting that failed on its own is not careless damage. But Tenancy Services is clear that tenants must tell the landlord straight away when they know something needs repair, and if they do not and the damage worsens, the landlord may be able to claim some of that extra cost. Careless-damage liability is capped at four weeks' rent or your insurance excess, whichever is lower.
Does moisture-resistant board stop water damage under the sink?
No, it slows it down. Laminex offers Melteca on moisture-resistant substrates alongside standard ones, and MR board holds up better against humidity and short wettings. But the limitation applies across the range: the substrate must not come in contact with any liquid. Specify MR because it buys weeks of margin, not waterproofing.
Getting a straight answer on your sink base
Send us a photo: torch on, door open, taken low so the back edge of the base floor is in frame. We can usually tell whether it is a reseal, one cabinet, or a conversation about the whole run — and we will say so when the answer is that it can wait. We have made kitchens in East Tamaki for 23 years and turn out ten-plus a week, so one sink base is a job we can slot in.
Bigger than one cabinet? Send the unit count and a rough scope and you will have a trade-priced number back inside 24 hours. We supply and install under one contract and one invoice, so there is no gap between joiner and fitter for the sealing to fall into — which, as above, is where it falls. Timing it around a tenancy change? Turning a rental kitchen around between tenancies is its own discipline.