Concrete is an indispensable building material, used worldwide for all types of structures. Durable in a wide variety of applications and site conditions, cit can nonetheless be compromised by water infiltration. Preventing water infiltration, therefore, is crucial to the safety and longevity of concrete structures.
Failure in concrete structures typically occurs within a tiny portion of the structure, and not within the overall waterproofing systems, according to building expert and author Michael T. Kubal.
“It is said that ninety percent of all water intrusion problems occur within 1 percent of the total building exterior surface area,” Kubal noted in Waterproofing the Building Envelope.
In other words, the majority of materials function effectively, while a small detail may cause all the problems. These problems don’t occur because of material failure, but because of “the individual components not being adequately detailed to allow the envelope to function as a cohesive unit. It is not the actual waterproofing materials or individual components that leak, but the junctures and terminations of these individual components.”
This idea, which Kubal has also popularised, is the 99% Principle, which states that 99 per cent of envelope leakage is due to factors other than material problems or system failures.
The other causes include:
- inadequate preparation work
- installation errors
- use of incorrect or incompatible materials
- use of incorrect amounts of product
- specification of the wrong system
The “junctures and terminations” Kubal spoke of are also called concrete joints. The different kinds of joints include:
- construction joints, which happen when new concrete is poured against existing concrete
- expansion joints, which allow for movement between adjoining building parts due to thermal expansion
- control joints, which help to control cracking due to temperature changes and shrinkage from drying
Concrete joints can be waterproofed in a number of ways, though three systems are used most often:
- PVC waterstops
- bentonite strips
- synthetic swelling rubber strips.
PVC waterstops are plastic sheets that are installed across a joint before concrete is poured, and are called “dumbbells” because of their shape. This system is inexpensive, but can be compromised in several ways. The material does not bond well with concrete and may bend while the concrete is poured, creating a tunnel for water infiltration. Shrinkage of the concrete can create gaps that also allow water infiltration.
While there are potential flaws, this product is generally effective. However, it is tedious to install, leading to errors that reinforce the 99% Principle. In other words, the product may be working effectively, but was not installed properly, so the system as a whole is compromised.
Bentonite strips are made from a type of hydrophilic clay that can expand substantially when exposed to water, sealing gaps and stopping water flow. The product comes in strip form and is easy to install, requiring no special equipment. The ends join together easily, creating an unbroken barrier, while it can also fill gaps and voids in poorly consolidated concrete.
Unfortunately, bentonite does come with some drawbacks, including:
- inability to swell sufficiently in saltwater or contaminated water
- a propensity to deteriorate over time
- the potential of swelling before the concrete pour if it comes into contact with water
Combining the characteristics of PVC and bentonite, synthetic rubber swelling strips are hydrophilic waterstops that can handle high hydrostatic water pressure, including below-grade applications, and harsh marine environments, and also expand to fill voids.
Synthetic rubber swelling strips can have a trapezoidal form, which can compact and expand readily when concrete is poured over it. Like bentonite clay, they can swell within a joint, but have a more controlled action.
This product can handle more extreme conditions, including freeze/thaw cycles, and then return to its original dimensions. Synthetic rubber swelling strips are not suitable for expansion joints, and they depend on proper installation, as do all similar products.