A Guide to Waterproofing Membranes: Purpose, Types and Key Reasons for Choosing Them

Water damage can come in different forms. From bubbling wall paint and discoloured flooring to musty odours and smells, mould buildup, and unusually high water bills. This can be caused by flooding, severe rainfall, faulty appliances, bursts, or clogged piping, among other causes. Either way, repair costs can soon balloon into the thousands if the core cause isn’t caught on time. Serious problems arise when enough water has accumulated to erode foundation walls and columns or walls and ceilings start sagging. Never mind the numerous health hazards, ranging from contaminated water supplies to pest infestations. 

A simple fix to limit and contain water damage is getting effective waterproofing membranes. This is a water-tight layer of resistant material applied to the external surfaces of your home, usually as a liquid-applied material or a sheet-based membrane. The primary purpose of membranes is to prevent water and moisture from penetrating key structural elements and to protect buildings and contents from water-related damage, such as rust, rot, or structural defects. Membranes also reduce health hazards, including mould and fungus growth. And they increase the resale value of your property with fewer maintenance and repair needs. 

Liquid Applied Membranes 

These are liquid coats that are directly applied to building surfaces to create a water-tight barrier. They work by forming a continuous and seamless layer in moist settings such as bathrooms, kitchens and basements. Liquid membranes are preferred for their elasticity, versatility for both indoor and outdoor use, and the fact that they contract or expand according to outside temperatures and humidity levels. There are three common types: 

Water/acrylic-based membranes 

Made from a combination of acrylic polymers and other additives, water/acrylic-based waterproofing membranes are highly resistant to water, easy to use, and very versatile. They can be sprayed, rolled or applied with a brush, have fast drying times, and good adhesion to common construction materials like concrete, metal and wood. Ideal uses are in roofing, balconies, patios, kitchens and bathrooms with good resistance to direct sunlight and UV exposure, rain and inclement weather. 

Polyurethane membranes 

Flexible, resistant to high water pressure and superior chemical and UV resistance make polyurethane membranes the ideal waterproofing solution in exposed areas, specifically roofing. They’re also used for foundations with their high elasticity to fill and bridge gaps. Downsides are their cost, more complex installation (due to higher VOCs) and longer curing times. 

Bituminous liquid membranes 

These are a mixture of bitumen, fibreglass, polyester and other materials. They’re common in roofing waterproofing projects (specifically flat roofs), as well as foundations and can be applied on vertical and horizontal surfaces. Commercial uses are in tunnels, bridge decks, road construction and as the preferred membrane when combined with insulation materials. When set, bituminous membranes proved excellent sealing, strong resistance to high temperatures and the required durability in demanding settings. Like polyurethane types, these also require more consideration during application, with proper ventilation the key factor. 

Sheet-Based Membranes 

These come in standard thicknesses of 2 to 4mm, are very durable, but more suited to flat surfaces, requiring careful installation and seam sealing. With that said, liquid membranes conform better to irregular surfaces and complex shapes, are generally cheaper and require less work when applying. Common sheet-based waterproofing membranes include: 

• Bituminous sheet – composed of bitumen, polymers and resins, these come in two types: self-adhesive and polymer-modified. Both are common in roofing and general waterproofing. 
• EPDM (Ethylene Propylene Diene Monomer) membranes – a synthetic rubber with high durability and weather resistance, used in flat or low-slope roofs, walls, basements, balconies and structural elements such as expansion joints. 
• PVC – a flexible and durable thermoplastic membrane commonly seen in waterproofing of basements, underground structures, foundations, pools and green roofs. 
• TPO – Thermoplastic Polyolefin is resistant to UV radiation, puncturing and various chemicals, making it ideal in both commercial and industrial waterproofing tasks. Common uses are in warehouses, factories, office buildings, tunnels, basements, water tanks and gutters. 

Other types are cementitious membranes  – generally durable, low-cost and easy to apply, with key uses in indoor settings; and various types of elastomeric membranes, preferred for their exceptional elasticity, flexibility and resistance to punctures and abrasions in complex builds. 

Factors to Consider When Choosing the Right Membrane 

Above or Below-grade? 

Above-grade membrane applications, such as roofs and balconies, must withstand temperature extremes, UV radiation, and be aesthetically pleasing. Common choices are polymer-modified bitumen, polyurethane and EPDM liquid membranes, and PVC and TPO sheeting. For below-grade use, consider types that bond well with the substrate and are resistant to high hydrostatic pressure. PVC, TPO and modified bitumen sheets also perform well here, as do polyurethanes and bituminous coatings. 

Durability and Longevity 

Membranes with high chemical resistance and elasticity, and those reinforced with materials like polyester or fibreglass, generally perform better at resisting water and moisture ingress. Strengthened polyurethane liquid membranes are highly regarded for their durability, but come at a cost. Less costly options are EPDM and bituminous sheets, though overall durability and longevity are also impacted by fewer seams and proper installation. 

Cost and Ease of Installation 

Cementitious and water/acrylic-based types top the affordability charts. Liquid-based variants will also incur lower installation costs and are usually faster to apply. Overall costs, though, also depend on durability, substrate bonding and compatibility, with TPO, thermoplastic elastomer, and polyurethane types at the other end of the price bracket.