Waterproofing a new hospital wing

by Darren

Richards Bay in KwaZulu-Natal recently added a new wing and parking deck to its Bay Hospital to meet the demands of an ever-expanding community. As waterproofing of the parking area was essential and since the client, the Netcare Hospital Group, expected a high-quality, long-term system, contractors WBHO Construction took a decisive step in changing the original specification to Sika’s superior Sikalastic 800 series.

To project-manage and proceed with this task, the contractor decided to invite Nukote’s technical group manager – a certified coating inspector – to the site. Meetings were held with Sika to establish a method statement, ensure timeous material delivery and draw up a quality-control system.

Strict adherence to over-coating times was stipulated – the first primer coat had to be applied overnight, then it should be wiped with MEK, and the second primer coat had to be applied in the morning. Later the same day, the surface had to be waterproofed and protected with the Sikalastic 800 products, dew point readings had to be conducted prior to and constantly during applications and substrate moisture content had to be measured using the Sika-Tramex meter with a maximum allowance of 4% pbw.

Industrial Linings & Concrete Laser Flooring was awarded the surface preparation subcontract. As the slab was poured in four sections and the south-side quarter exposed to a rainstorm during construction, surface preparation was significantly delayed. The initial visual inspection showed a soft powdery surface and a fair amount of surface laitance, leading Sika to initiate a second shot-blasting. This resulted in exposed aggregate and a rough profile.

Before priming and waterproofing the deck, a scraper coat of Sikalastic EP Primer 11 was applied to fill surface irregularities and to eliminate or reduce blow and pin-holing caused by outgassing.

The first coat of Sikalastic EP II Primer was thinned down with 15% epoxy thinners and the second coat was thinned down with 5% epoxy thinners. This two-part epoxy-polyamine primer is used for priming concrete substrates, cement screeds, metal and plywood, and can be used for internal as well as external surfaces. It offers low viscosity, good penetration ability, high bond strength, easy application, short waiting times and is good as a multi-purpose primer.

Using the spray method, the primed surface area was then waterproofed with 4 560 litres of Sika’s multi-purpose Sikalastic-841 ST, a two-part, pure polyurea membrane that contains 100% solids with zero VOC.

Applicable in a wide temperature range, this product is UV-resistant, has excellent crack-bridging properties and provides excellent corrosion protection. A 2mm thick layer was sprayed onto low traffic areas of the deck, whilst high traffic areas, including turning circles, were sprayed 3mm thick.

The fast reactivity and curing of this excellent product allows for almost immediate return-to-service time – cars were able to drive directly onto the deck, testament to the durability and robustness of the Sikalastic system.

To complete the waterproofing and protection process, the deck was sprayed with a 0,5mm thick coating of Sikalastic-845 AL Aliphatic, a two-part, flexible, 100% solids, pure polyurea membrane with very similar properties to Sikalastic-841 ST. To produce a non-slip effect, a stippled finish was specified. Termination grooves cut in the slab for flashing detail, as well as construction joints and entrance and exit ramps, were sealed with Sikaflex PRO-3 WF, a moisture-curing, one-part, elastic joint sealant based on polyurethane.

While the Nukote inspector was still on site, the contractor focused the spray applications on the north end of the slab and then shifted focus to the south side once a 58m2 area had been prepared.

Weather played havoc during this project, which commenced in October 2011 and was only completed approximately six weeks later. Continuous rain during priming coats, as well as during the application of Sikalastic-841 ST, rendered it impossible to adhere to over-coating times. To add to these on-site challenges, the rain was accompanied by strong winds, resulting in over-spray.

Despite the adverse weather conditions experienced, Sika’s world-class products won the day and Netcare Hospital Group is proud of its top quality, long-lasting parking deck serving the busy Bay Hospital.

Sika South Africa
Tel: 031 792 6500
E-mail: headoffice@za.sika.com
Website: www.sika.co.za

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