LeDeuxions · notes from twenty years on site · 한국어
When a building leaks, most people look up. A basement is the opposite. The water is not falling from above — it is being pushed up through the slab and in through the walls by the pressure of the water in the ground. Once you know that, everything about basement waterproofing looks different.
I saw this on an actual job. A public building, stone floor in the basement. Step on it and water came up through the joints between the slabs. Water had collected underneath, and the weight of a footstep was enough to push it back out.
That is what hydrostatic pressure does. Roof water falls politely, following gravity. Groundwater presses — against the floor, against every wall, all the time, from every direction at once.
Under a basement slab you lay waterproofing membrane — poly sheeting — in layers. Two layers, three. It is not expensive material. And yet this is exactly where jobs cut corners. One layer instead of three. Sometimes none at all. It happens on work that is under budget pressure, and the reasoning is always the same: it's just plastic.
The outcome is reliable. Within a few years water is coming up through the floor, and every finish in the basement has to come out. The repair costs hundreds of times what the sheeting would have cost.
A basement is one of the few places where redundancy is never wasted. The reason is simple: if one layer is breached, the next one still holds. With a single layer, one small defect anywhere and it is over. You cannot inspect what is under a poured slab, and you cannot fix it without breaking it.
And you must give the water somewhere to go. Interior drain, exterior drain, weeping tile — the specific method matters less than the principle. Blocking water is a fight you eventually lose. Draining it is honest. Water is meant to move, not to be trapped.
People want a garden over the basement. Soil, planting beds, a tree. That soil holds every rainfall like a sponge, directly above the waterproofing layer, and the water works its way down. A pretty layer of topsoil is a very common reason a basement is under water five years later.
Landscaping above a basement is not a landscaping decision. It is a drainage decision, and the drainage has to be designed at the same time.
Basement waterproofing is not where you save money. What you save here comes back as demolition, as tearing out walls, as a repair bill with two more digits on it.
There is no such thing as a house that is both cheap and good. If you think you have one, it may only mean that not enough time has passed for it to show.
In construction there is almost never an absolute — there is usually a better way waiting to be found. Basement waterproofing is the rare exception. The better way is already known: do it properly, do it in layers, and give the water a path out.
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Written from jobs I worked on, not from a manual.
Small tools I built for everyday work — pdf300.com
And a few things to play with — ledeuxions.com/games