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Dealing with Magnesite Problems in Sydney’s Residential Units

In the 1960s and 70s in Sydney, the use of magnesite as a floor covering was common and widespread in residential unit development. Since its installation, it has become evident that after a period of 30 years or more, and due to long term exposure to household moisture and/or water through balcony doors, the magnesite has been the source of chloride ingress into the concrete slab. This has led to the corrosion of the steel reinforcement in the concrete floor, resulting in cracking, spalling and ‘lumping’ of the concrete below the floor covering, with the condition commonly referred to as ‘concrete cancer’. 

During the initial condition assessment, the full extent and severity of the problem must be properly identified. This is the most important stage and is critical for selecting the correct remediation option. The best approach is to undertake an electrochemical assessment of the concrete slab which will reveal the level of chloride in the concrete and identify the level of corrosion of the embedded rebars. Subject to the test results, it is likely that the most straightforward and permanent repair solution can be implemented. This solution includes the removal of the magnesite topping, removal of all chloride affected concrete, cleaning of the rebars, and applying new concrete. However this repair solution may not be a viable option in some cases due to structural considerations.    

While the above method can potentially be a permanent and sound long term solution, a range of alternative options do exist. These remediation options include; the application of an impressed current cathodic protection system, the application of a chloride extraction system (desalination), the application of sacrificial anode systems around the repair areas and within the good but chloride contaminated concrete areas for corrosion prevention, or the application of sacrificial anodes around the repaired areas combined with the sealing of the remaining area of the floor slab to prevent further ingress of moisture to the embedded steel. These alternative methods have their own limitations. They can only be implemented subject to certain circumstances including the extent of concrete deterioration, consideration of cost, long term monitoring and maintenance, and other building-specific conditions.

The selection of the optimum solution for each specific case starts with carrying out a detailed condition assessment of the floor slab following the magnesite removal. Remedial Technology has been involved in the assessment of various magnesite flooring problems and has delivered suitable and long term solutions in each individual case.

Author: Atef Cheaitani
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