Monday, November 21, 2011

Some facts about waterproofing membranes

Waterproofing membranes have come a long way in the past few years. That said there always seems to be a huge number of products on the market. So what makes a membrane effective, and how do you know what is the best product for you?
Ideally, a waterproofing membrane should:
- Protect the substrate from moisture
- Have high elongation before breaking point
- Dry quickly (and doesn’t skin)
- Dry without being stressed
- Be able to be bonded (eg. with tiles)
- Have high chemical and abrasion resistance
- Be easy to apply
- Be safe to handle and non-toxic
These days, there are two common classes of waterproofing membrane: acrylic and polyurethane. Polyurethane has a higher tensile strength and stretches more. However, they often have solvent based components that are less safe to use. Bonding to them can also be problematic. Acrylic usually takes longer to dry and is less resistant to abrasion and some key chemicals.
A good waterproofing membrane needs to provide a waterproof barrier but it must also cope with expected movement. This type of movement, such as that at joints and junctions, can easily be accommodated with bond breakers. They allow the membrane to stretch rather than snap, taking advantage of the elastic property of the material. Figure 1 is a representation of what can happen when no bond breaker is used on a wall/floor junction. Figure 2 shows how a bond breaker can accommodate the movement by allowing the membrane to stretch more. The basic idea is much like an elastic band. A long piece of elastic will stretch further before snapping than a short piece of the same material.
The problem lies in how much the membrane needs to stretch to accommodate unexpected cracks (those not treated with bond breakers). As the extension (movement) is more than the elongation (stretch) capacity of the membrane, it will result in a tear in the membrane potentially leading to leaks.
So basically if the movement is more than the membrane can stretch, then it will snap. A bond breaker allows the membrane to stretch a lot more.
Installing the required bond breakers is always important. However the design of the membrane can also help. A membrane that is stronger with more stretching capacity means that it is more forgiving and the bond breakers can be narrower. Essentially the better the elongation, the later it will break and the stronger the membrane’s internal (or tensile) strength, the more likely it will de-bond and stretch rather than snap. Remember that it is always best to install a bond breaker in all areas that are likely to move.

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