Waterproofing of parking decks should be specified according to the type of wearing surface required, advises a.b.e.®‘s waterproofing specialist, Gordon Anderson.
a.b.e.® and Chryso SA should be consulted right at the outset of any parking deck waterproofing project to prevent failures such as pictured above.
by Gordon Anderson, Waterproofing Consultant at a.b.e.®
The options available in the South African market for the waterproofing of parking decks are varied and should only be specified after consideration of the type of the finished wearing surface required.
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. The construction details that require special attention on parking decks are the water outlets and expansion joints: the drainage outlets being at the low points and expansion joints at the high points.
Dealing with the more traditional methods first, the a.b.e.® recommendations how the deck can best be rendered watertight follows:
- The “Black Top” or premix can be either hot or cold applied The waterproofing system most commonly recommended by a.b.e.® is a double layer system comprising 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 Black Top is probably the cheapest of the wearing surfaces but in the hot climes of South Africa does not always give a good long-term solution due to lack of stability when subjected to the forces exerted by vehicles with power steering in tight turning /parking situations. A geotextile layer over the installed waterproofing system prior to the installation of the wearing surface is beneficial in the longer term.
- Brick pavers or interlocking blocks on either a clean sand bed,or on a mortar bed have been proven to provide a decorative and effective wearing surface. The a.b.e.® recommended waterproofing specification is a double layer system comprising of an Index 3mm membrane followed by an Index 4mm membrane laid with staggered side laps and end laps. The 3mm membrane is fully sealed by torch fusion to the primed substrate and to the overlaying 4mm membrane. The need of a separation/ protection membrane laid over the waterproofing is essential when a mortar bed is to be used, the basic rule being to not trap a membrane between two cementitious layers that move separately. The need for the separation layer is less so when a clean sand bed is the base. The need for adequate drainage on a sand bed is important due to the fact that when the sandbed becomes super-saturated it has poor cohesive strength allowing for displacement of the wearing surface and possible damage to the waterproofing system in addition to giving an uneven surface that could lead to accidents.
In recent times there has been growing interest in alternative waterproofing systems for parking decks. A brief outline of two of these system types, one being from the polyurea /polyurethane family, the other from the chrystalline family, may be of interest. a.b.e.® has the products and technology skills that cover both of these categories. There are benefits from both the polyurethane/ polyurea and Chrystalline systems – the main one being that no wearing surface is required.
- Polyurethane/ polyurea in the parking deck application can be delivered by a high pressure spray rig which requires strict control of both mix ratios and temperature. If this is not controlled, it will lead to an off-specification product and failure. The surface preparation is critical, often requiring vacuum or water blasting followed by a primer and having a substrate of no lower strength than 25Mpa. The coating when applied cures quickly allowing for light traffic in under 5 minutes and rapid full cure. A trained crew can produce around 1000sq m of such waterproofed parking deck surfaces per day. a.b.e.®‘s VIP polyurea system has an international reputation and track record and a.b.e.® has an exclusive distribution agreement covering its areas of operations with the VIP company in Germany. To obtain best results from this system, the specification should be drawn up in consultation with a.b.e.® specialists. A recent addition to the a.b.e.® polyurea range is a low pressure system which can be used on smaller projects. The polyurethane/olyurea product is available in a range of colours which facilitates the demarcation of parking areas in complementary colours.
- The a.b.e.® Krystalkote range and the CWA 10 range from a.b.e.®‘s holding company, Chryso Southern Africa, can protect and waterproof concrete structures through the crystallization 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, thus waterproofing the structure against penetration of water and other liquids from any direction. Krystalkote and CWA 10 give a strong lasting protection against dampness and hydrostatic ground water pressure. One of the major benefits that is often claimed with some justification is that a chrystalline waterproofing system will re-seal over a period of time if sufficient moisture is present, but until the chemical reaction is complete the leak will continue. The type of crack is important, by way of 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 characteristics and properties of a concrete mix may be altered by the addition of the chemicals and water to a designed mix and this is where a.b.e.®/Chryso can offer assistance from the Chryso Group’s fully equipped and staffed concrete mix laboratory who will assist in the defining and testing procedures to provide the required concrete mix in collaboration with engineering professionals.
In summing up: 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.® and Chryso should be consulted right at the outset of any such project to provide the necessary technology to prevent failures.