Reports on the death of bentonite clay active waterproofing membranes have been greatly exaggerated
Once the default product choice for architects and engineers, waterproofing membranes of active bentonite clay have suffered under a cloud of distrust in recent years. The advances in pre-applied bonded membranes and water-tight concrete systems have turned heads and design professionals have moved away from their old faithful friend.
So what has led to this sea change? Probably, it has been driven by the amount of failures and remedial issues that seem to have arisen with bentonite waterproofing membranes, but is this a fair assessment of bentonite or are there other factors to be considered.
We argue that bentonite waterproofing membranes, specifically ones designed for structural waterproofing can provide as high a level of efficacy, in terms of the prevention of water ingress, as any other system on the market.
The problem is that not all bentonite systems being offered on the market are specifically designed for structural waterproofing. Currently there are many landfill and pond-lining membranes being sold into a price driven market which meet theoretically based laboratory tests but do not perform under site conditions. Also, sometimes contractors are being allowed to install these membranes without proper training or instruction so more often, than not, application errors lead to failures. Additionally important accessories that help the membrane to fulfil the required standards are not being sold or purchased in attempt to keep the cost down which once again weaken the integrity of the liner. The old adage ‘penny wise, pound foolish’ comes to mind.
Fortunately for us at SURFASOLOGY we produce and sell the bonded membranes and water-tight systems but we are also seeing a resurgence in our bentonite membrane business. What are the reasons behind this?
Well the obvious one is cost but secondly our CEMtobent systems are specifically designed for waterproofing reinforced concrete structures below grade.
While most bentonite clay active membranes are sheets of sodium bentonite clay sandwiched or needle punched between two layers of geotextile or bentonite fixed to a foil membrane, CEMtobent is a triple layer system. The primary liner is a PE 3-D composite layer which contains a layer of sacrificial bentonite which prevents the pre-hydration of the bentonite while the membrane is being placed; the second sheet is fully fledged bentonite waterproofing liner with a honeycomb layer which provides stability for the main body of the bentonite. The third and final layer is a watertight PE coated fabric sheet which provides the added protection of being both root-resistant and radon tight. These three layers are stitch bonded, using a patented technique, which enables the active bentonite layer to remain stable during vertical application.
Another important advantage of the CEMtobent system is that the active layer is in the form of powdered bentonite, not granulated. This gives the active layer more surface area which improves the absorption capability thus improving the waterproofing efficacy of the membrane.
Our CEMtobent systems have recently been applied in RCSI York Street which is Ireland’s deepest basement project this year, and are currently being applied in the Germany Railway Authorities huge infrastructure redevelopment project – Stuttgart 21.