Gordon Anderson from a.b.e. Construction Chemicals discusses traditional and new waterproofing methods for parking decks.

By Gordon Anderson, waterproofing consultant at a.b.e. Construction Chemicals, part of the Chryso Southern Africa Group.

The waterproofing of parking decks should only be specified after consideration of the type of the finished wearing surface. All substrates, either post-tensioned or coffered, should be cast or graded to fall to outlets, and should be smooth and free of voids or protrusions.

Traditional methods
Whether choosing a blacktop or premix that can be hot or cold applied, or brick pavers and interlocking blocks, a double-layer waterproofing system is recommended. This comprises of an Index 3mm membrane followed by an Index 4mm membrane, laid with staggered side laps and end laps. The 3mm membrane should be fully sealed by torch fusion to the primed substrate and to the overlaying 4mm membrane.

The blacktop is often the cheapest wearing surface, but in hot climates not always the best long-term solution. A geotextile layer over the installed waterproofing system, prior to the installation of the wearing surface, is beneficial in the longer term.

Opting for brick pavers or interlocking blocks on a mortar bed creates the need for a separation/protection membrane to be laid over the waterproofing, the basic rule being to not trap a membrane between two cementitious layers that move separately. When a clean sand bed is the base, the need for the separation layer is less so but adequate drainage is important because when the sand bed becomes super-saturated, it has poor cohesive strength allowing for displacement of the wearing surface and possible damage to the waterproofing system.
    
Alternative systems
The main benefit of alternative waterproofing methods for parking decks, such as using polyurethane/polyurea and chrystalline systems, is that they don’t require a wearing surface.

Polyurethane/polyurea can be applied by a high pressure spray rig which requires strict control of both mix ratios and temperature. The surface preparation is also critical, often requiring vacuum or water blasting followed by a primer and having a substrate of a minimum strength of 25mPa. The coating cures quickly, allowing for light traffic in less than five minutes, and a trained crew can produce about 1 000m² per day. The polyurethane/polyurea also comes in a range of colours, which facilitates the demarcation of parking areas.

Other systems such as the Krystalkote and the CWA 10 ranges protect and waterproof concrete structures through a crystallisation process. The active chemicals in the product reacts with the moisture in the concrete, resulting in a chrystalline formation within the pores and the capillary tracts of concrete, thereby waterproofing the structure against penetration of water and other liquids from any direction.

A chrystalline waterproofing system can also re-seal a crack over a period of time if sufficient moisture is present. The type of crack, however, is important, for example a passive crack can reseal but a dynamic crack will never seal as the formed chrystalline structure will be broken down by the recurring movement.

The new entrants to the waterproofing of parking decks arena all have potential, but must be supported with the proper product and application technology.

a.b.e. Construction Chemicals
Tel: 011 306 9000
Website: www.abe.co.za