Construction defects: waterproofing, part 3

Construction defects: underground waterproofing, design versus execution, part 3

By: engineer Ron Arad, Arad Bedek Bayit

Earlier installments covered the core waterproofing principles and looked at concrete as a waterproofing material, including the conditions under which it actually seals. This article continues with the failure points in underground waterproofing that lead to construction defects.

Finding these waterproofing defects, and advising on how to fix them, is part of the engineering inspection a home inspection engineer carries out on an apartment to identify construction defects, as part of a home inspection process.

Failure points behind construction defects and underground waterproofing: continued

1. Missing pile caps

For various reasons, pile caps are sometimes skipped.

Without a pile cap, waterproofing cannot be applied.

Pile concrete is not built to bond with waterproofing: it is rough, without straight lines, which makes it effectively "hollow" from a waterproofing standpoint. A square or rectangular pile cap provides the neat, horizontal surface the waterproofing needs to bond to.

2. Pipes penetrating the floor and walls

As noted, the detail where concrete meets a pipe, or the sleeve carrying it, is complex and often a point of disagreement between planners.

Planning parameters matter too. The detail for a pipe penetrating a roof, for instance, is different from one penetrating a water tank.

3. Checking the waterproofing

In most cases, waterproofing cannot be tested until winter arrives. Flood tests of various kinds are difficult to run, and are usually skipped.

By the time a leak turns up, the building is already finished, sometimes already occupied, and the contractors, let alone the planners, have long since moved on to other projects.

4. Access for repairs

Underground waterproofing is usually very hard to access for repairs, sometimes impossible. That calls for expensive, complicated solutions that do not always work the first time.

5. Spray-applied waterproofing

Spray waterproofing is usually applied to walls, and needs to reach a thickness of about 4 mm.

Hitting that thickness across the entire surface is difficult, and patches often end up with far less waterproofing than required.

6. Curing

Concrete cures for 21 days after it is poured. Curing, keeping the surface wet, lets the concrete dry in a way that prevents cracks and other problems.

Very often, time pressure means the waterproofing goes on before that 21-day wait is up.

Applying waterproofing before the concrete has fully dried releases vapor from the concrete that detaches the waterproofing membrane from the surface, and from there it is a short step to water getting in.

7. Rebar stubs and concrete protrusions

Rebar stubs and concrete protrusions left in place after the pour puncture the waterproofing, or leave an air gap between the waterproofing and the wall.

The wall needs to be smooth and clean.

Simply cutting off the protruding rebar is not a proper fix: the cut end still corrodes and swells well beyond its original size, since rust takes up far more volume than the iron it replaces, and that swelling punches a hole through the membrane.