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A quick reference guide on the what and where of waterproofing.

Waterproofing is an important part in any build but with such a wide variety of products and systems available, it can be tricky to know which one to specify for a specific project. Walls and Roofs compiled a quick reference guide on the what and where of waterproofing.

Bitumen

Bitumen is a byproduct of crude oil. The quality of material and ease of production depends on the source and type of crude oil from which it is derived. Thanks to bitumen’s well-known waterproofing qualities, it is widely used in various forms.

It is available in three formats:

• Torch-on bitumen waterproofing membranes uses heat to fuse the bitumen directly onto the surface. It is most often used for flat roofs, but can also be used for retaining walls, basements and below-ground structures, bridges and other structures.

Advantage: High resistance to mechanical damage and punctures.

• Bitumen liquid-applied membranes are polymer-modified bitumen emulsions which do not require a torch application. It is mainly used for waterproofing foundations, roofs or retaining walls.

Advantage: Fully-bonded, seamless system with crack-bridging capability.

• Self-adhesive bitumen membranes and tapes are cold applied. They are well suited for small areas, vertical surfaces or areas with difficult access.

Advantage: No special equipment is required.

Note: Tiling over bituminous waterproofing systems can be problematic. Being thermoplastic in nature, bitumen in warm conditions tends to be viscoelastic (‘flow’ as a solid mass). In extreme cases this flow exceeds that achieved with deformable (flexible) adhesive and grout systems, and movement joints combined, resulting in “buckling” of the panel, cracking of tiles and ultimately failure. Installing a screed, of suitable thickness over the bituminous waterproofing compound is recommended.

Liquid applied membranes (LAM)

Liquid applied membranes are monolithic, fully-bonded, liquid-based coatings, typically polyurethane or acrylic-based, which cure to form a rubber-like elastomeric waterproof membrane.

• Polyurethane-based products are well suited for use on interior and exposed exterior surfaces, including parking areas, bridges, parapet walls and small flat roofs as they are resistant to foot traffic and standing water.
• Acrylic-based products should only be left exposed on non-trafficable roofs and parapet walls, and should be protected with suitable coverings, such as tiles, on installation areas exposed to frequent trafficking to prevent damage to the waterproofing layer. Some acrylic options are fibre-enriched for improved crack-bridging capabilities, negating the need for reinforcing membranes in the main area application, these only required for “critical” areas, such as vertical and internal corners and interfaces, around drains, etc.
• When used on roofs, or where there is movement in the background, manufacturers often specify the need for a non-woven polyester membrane to waterproof flashings and parapet walls as well as for sealing joints, laps and roofing screws on corrugated roofs.

Advantage: ready to use, easy application and compatible with cementitious tile adhesives and levelling compounds.

Note: When left exposed, regular maintenance inspections should be carried out, and remedial work carried out as soon as any damaged or deteriorated areas of waterproofing are found.

Cementitious waterproofing compounds

Cement-based products that are available as waterproofing compounds, or mortars.

• Two component flexible cementitious compounds are used to waterproof concrete substrates on balconies, patios, bathrooms, showers, swimming pools and ponds prior installation of tiles. It can also be used exposed on non-trafficable roof slabs and parapet walls. Options also include reinforcing the installation with a polyester membrane, and fibre-enriched formulations for enhanced crack-bridging in shower recesses and internal wet areas. If leaving exposed, be sure to confirm that the product offers high UV resistance.

• Waterproofing mortars are supplied as ready-to-use solutions which are used to seal against damp soil, seepage and percolating water. These products are often applied in water reservoirs, water retaining structures, basements and other engineering structures.

Advantage: Compatible with cementitious tile adhesives and levelling compounds.

Self-healing products

Crystalline products react with the water and free lime in concrete, to form crystals which effectively fill any small voids within the concrete and make it watertight. It can also be used as a self-healing product to repair cracks in the concrete, as the crystals will continue to grow over time. These products are available as either a powdered crystallising admixture or a crystalline cementitious penetrating coating.

Advantage: Chloride free, safe to use with potable water storage, wastewater etc.

Waterstops

A specialised and technical product, designed for waterproofing construction joints with preformed flexible strips. Waterstops are used for construction joints in dam walls, reservoirs, sewerage tanks and other water-retaining structures constantly exposed to hydrostatic pressure.

There are two types available:

• Composite flexible strips that are hydrophilic and swell when in permanent contact with water. This forms an active barrier against pressurised water, both positive and negative. Installation is with a hydrophilic adhesive and sealant to concrete, metal and natural stone. It is important to note that these are not to be used in expansion joints.

• PVC extruded flexible strips that come in a range of profiles for different types of construction joints. These can be installed at the centre section of the wall, kickers and day work joints, or in the rear of slabs and walls. Internally placed waterstops (centre fix) are embedded into the concrete, while externally placed waterstops (rear fix) are installed with mechanical fixings.

Full thanks and acknowledgement go to www.abe.co.za, www.mapei.com, www.tal.co.za and www.zaf.sika.com for the information used in this article.

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