Project & Insights
Can you waterproof an elevator pit with water actively running in?
August 17, 2026
By Boris Gopka, Owner, JSW Waterproofing — elevator pit waterproofing across Toronto and the GTA
You cannot waterproof an elevator pit while water is running into it, and the reason is simple: nothing bonds to a surface with water moving through it. The flow has to be stopped first, using a material that expands on contact with water and plugs the crack for about four hours — and everything else has to be finished inside that window.
It is the single biggest driver of cost on a pit job, and the one most quotes are vague about.
Why active water defeats a normal repair
Put it in plain terms. You have a crack with water flowing out of it into the pit. You try to press a patch into that crack, and the water coming out washes the material away before it sets. It does not matter how good the product is. It is being rinsed out of the opening faster than it can grab.
The same applies to the coating. A polyurea membrane needs a dry, sound substrate to bond and cure against. Applied over a wet or actively seeping area, it either fails to adhere there or lifts later when pressure builds behind it.
So the sequence has to change. Stop the water, then repair.
How the flow is actually stopped
Stopping an active leak in an elevator pit wall means routing deeper into the crack that is supplying the water, then injecting a material that expands violently on contact with water. The reaction is what makes it work — the material meets the flow and swells into the void, forming a plug against the pressure behind it.
That plug lasts about four hours.
It is not the repair. It is a temporary block that buys enough time for the real work, and the whole job is then structured around that window. The crack sealing and the waterproofing go in immediately and have to cure while the plug is still holding. Once the material has cured dry, it is the permanent barrier and the plug behind it has done its job.
Between stopping the flow and applying the waterproofing, the wall is dried out with specialised equipment. There is no point winning four hours and then coating a damp substrate.
What this does to the schedule and the price
Fighting water drives the cost of an elevator pit job up hard, because the flow-stopping is a full operation that happens before the work you are actually paying for begins.
On a group of residential buildings in the Hamilton area we spent two full days doing nothing except stopping water so the wall repairs could start. Two days of crew time, before a single square foot of waterproofing went on. Those buildings had unusual pressure behind the walls — on one of them the original design routed the perimeter weeping tile through the elevator shaft to channel groundwater to the sump pit, so the shaft was being fed continuously and heavily whenever it rained.
Not every active leak is that severe. At a mid-rise in North York with five pits, one had an active leak that had already flooded the pit, and stopping it with hydraulic cement was a step rather than a two-day operation before the cold joints and coating went in.
That is at the extreme end. But it shows the shape of the problem: a pit with water actively running in is not the same job as a dry pit with a hairline crack, and pricing them the same is how a contractor ends up either losing money or cutting the flow-stopping step.
When stopping the water is the wrong goal
There is a case where sealing everything is the wrong answer, and it is worth naming here because it comes up on exactly the pits that have the worst active water.
Where the hydrostatic pressure on the walls is severe and constant, sealing the pit completely just accumulates that pressure with nowhere to go. On block walls especially, relieving the pressure through drilled relief drains is the better engineering answer even though it has real drawbacks. Stopping the flow to install a repair is one thing; trying to hold back an indefinite volume of groundwater with a coating is another.
What a property manager should ask
Ask any contractor quoting your pit what they will do if water is running when they open it.
The answer tells you a lot. A contractor who has done this work will describe stopping the flow, drying the substrate, and working to a window. A contractor who has not will talk about the membrane. Coating over active water means doing the pit twice, and the second attempt costs more than the first because the failed material has to come off before anything new goes on.
If your pit currently has visible running water rather than standing water, say so when you book the inspection. It changes the crew, the materials and the day.
Book a JSW inspection · More on elevator pit waterproofing and concrete crack repair
Common questions
Frequently asked questions
Why can't you just patch a crack that has water coming out of it?
Water flowing out of a crack washes the repair material out before it can set. Anything you press into the opening — patching compound, cement, sealant — is carried away by the flow, so the repair never gets the chance to bond or cure. The water has to be stopped first, and stopping it is a different operation from repairing the crack.
How long does a leak plug last?
The water-reactive plug we inject to stop an active leak holds for roughly four hours. It is a temporary measure by design, not a repair. That window is what the permanent work has to fit inside — the crack gets sealed and the waterproofing applied while the plug is still holding, so it cures dry.
Does active water in the pit make the job more expensive?
Active water raises the cost of an elevator pit job significantly, because stopping the flow is a whole operation before the actual repair begins. On a group of buildings in the Hamilton area we spent two full days doing nothing but stopping water so the wall repairs could start. That is two days of crew time before any waterproofing was installed.
Do you have to dry the pit out before waterproofing it?
The substrate has to be dry for the waterproofing to bond and cure, so yes — once the flow is stopped, the wall is dried with specialised equipment before the application goes on. This is also why power washing a pit during cleaning is a mistake: it saturates the concrete and creates the same problem deliberately.
What happens if a contractor coats over active water?
Coating over active water means doing the job twice. The coating either fails to bond in the wet area or lifts later as water pressure builds behind it, and the second attempt costs more than doing it properly the first time because the failed material has to come off. If a quote does not address how active water will be handled, that is worth asking about before signing.
