Water Sitting in Your Carpark Pothole? The Countdown
A recent inquiry from a big-format retailer on the North Shore ticked a box most people skip: "Is water pooling or sitting in the damage?" Yes. One pothole, busy public carpark, depth unknown because nobody fancied standing in it with a ruler.
That one tick changes the whole assessment. A dry pothole is a surface problem. A ponding pothole is a base problem being actively made worse every time it rains, and in an Auckland July it rains most days.
What standing water actually does
Asphalt doesn't really fail from the top down; it fails from underneath. The black surface layer is thin, usually 25 to 40 mm in a carpark, and everything below it is compacted metal basecourse doing the real structural work. That base stays strong only while it stays dry and dense.
Water sitting in a pothole has an open door to that base. Every car that rolls through the puddle pressurises it, and pressurised water moves fines: the small particles that lock the basecourse together get pumped out to the edges as grey slurry. You've seen it, the muddy halo around a puddle in a carpark. That halo is the base leaving.
So the hole grows in three dimensions at once. Wider, because the saturated edges break off under wheels. Deeper, as the base loses material. And, invisibly, sideways under the intact asphalt around it, which is why a ponding pothole patched late often needs three times the area cut out; the surface around the hole looked fine but was floating on softened base.
The retail-specific problem
For a store, a wet pothole is two problems wearing one hi-vis vest. There's the pavement problem above, on the clock but quotable. Then there's the people problem: customers stepping around or into a puddle of unknown depth, trolleys slamming through it, prams detouring into the drive aisle. A pothole a customer can see the bottom of is an annoyance. One full of opaque water is a hazard claim with a court date attached, because nobody can judge what they're stepping into.
Under the Health and Safety at Work Act a store's carpark is part of its workplace. Knowing about a ponding hazard and leaving it through peak trading weeks is exactly the fact pattern that looks bad in hindsight. The fix costs less than the paperwork.
What "act this week" looks like in practice
You don't need to close the carpark or wait for summer. Hot mix asphalt goes down fine in winter as long as the base is prepared properly; the myth that asphalt work stops in July mostly protects contractors who'd rather not work in the rain. What a wet-winter repair needs is a crew that dries and re-compacts the base before filling, rather than tipping cold mix into the puddle, which lasts about a month and then you've paid twice.
Timing wise, one patch in a trading carpark is a few coned-off parks for part of a day. Early morning starts mean the area is back in service before the lunch rush. A written fixed price comes first, from photos, so whoever approves spend sees the number before committing to anything.
Reading your own carpark
After the next decent rain, walk the carpark and note every spot still holding water an hour later. Those are your next twelve months of potholes, in order. Some are already holes; some are just depressions where the surface has started to deflect. Photograph the lot. Fixing the two that have already broken through while treating the three that are about to costs far less than meeting each one individually over the next year, for the mobilisation reasons covered in our industrial yard costing post.
Frequently asked questions
Can you patch in the rain?
Light drizzle, yes, with the right prep. Heavy rain, no; we reschedule rather than lay a patch we'd be back to redo. Auckland gives us enough dry windows even mid-winter that jobs rarely slip more than a day or two.
The puddle drains after a few hours. Still urgent?
Slow draining means the water is going somewhere, and that somewhere is your basecourse. It's the same damage on a slightly longer clock.
Who pays if the carpark is leased?
Depends on the lease; outgoings clauses usually put pavement maintenance on the tenant, structural repair on the landlord. Our quote PDF is written so you can forward it to whichever side of that argument you're on.
If your carpark has a pothole that doubles as a birdbath, photograph it while it's wet, then again dry if you can. Send both through the quote form and there'll be a fixed price in your inbox before the next front comes through.
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