Construction defects: waterproofing, part A

Construction defects: underground waterproofing: planning versus execution, part A

By engineer Ron Arad, Arad Bedek Bayit.

The first waterproofing in history:

The first documented waterproofing in history succeeded about 4,000 years ago, and the man behind it was Noah.

And it followed a technical specification set by God:

It was a huge ark, home to thousands of animals, maintained by Noah and his three sons.

Needless to say, Noah and his sons had no time to deal with waterproofing repairs, so it's safe to assume the "kofer" coating held up.

According to Rashi's commentary, kofer is Aramaic for pitch. The Torah also mentions kofer for the ark of Moses, which was coated with it only on the inside.

Rashi explains that Noah's ark was coated with pitch on the outside too, because of the force of the water.

Pitch is the same material used in most waterproofing today: a bituminous substance used to make bituminous sheets and coatings.

So if 4,000 years ago one person managed to waterproof a huge ship that sailed at sea for a whole year, why do more than 30% of the structures in the country today suffer from waterproofing defects?

Principles of underground waterproofing

Underground waterproofing that actually prevents defects follows several guiding principles. Here are a few:

• Whether the ground is permeable (sandy) or clayey: clay soil needs drainage arranged for it.
• The type of water in contact with the structure: brackish water, for instance, calls for waterproofing materials and concrete grades able to withstand an aggressive environment. The concrete mix, the required additives and the concrete cover over the rebar are all critical when the water is brackish or seawater.
• Access to the structure: whether an existing building sits right next to the planned one in a way that could interfere with doing the waterproofing, or maintaining it later.