Huge Cost Per Unit in Fixing Floor Hazard

As governments and the building industry focus on managing combustible cladding issues, another crisis looms over the use of a flooring material known as magnesite, experts warn.

Potentially affecting tens of thousands of apartments built from 1960 through to the 1980s, the little-known magnesite-related defects are also more expensive and invasive to fix.

Magnesite, which was commonly used as a floor topping or levelling product, contains glue. When magnesite absorbs water, the glue can leach into concrete floors and corrode steel reinforcement bars, causing the concrete to expand.

The City Futures Research Centre at University of NSW said that in NSW alone there were more than 14,000 strata schemes containing more than 186,000 lots or units registered between 1961 and 1979.

Peter Johnsson, associate principal with engineering consultancy firm ACOR, said up to 90 per cent of apartments built during that period had magnesite in their flooring, particularly in Sydney’s eastern suburbs, northern beaches and western suburbs.

AFR magnesite story

‘‘The cost to fix this issue can range from $30,000 for an apartment . . . to over $100,000 today,’’ he said.

Marton Marosszeky, director at BCRC, a group of consultants specialising in construction materials, said owners of older apartments needed to be aware of the problem.

‘‘It’s a looming problem that’s coming towards us at a fast rate,’’ he said.

‘‘There are thousands of buildings built in that era with magnesite floor topping. This could potentially eclipse the cladding issue. But because it’s hidden and slow to manifest, it’s not getting a lot of attention.’’

Mr Marosszeky said one of the magnesite-related jobs BCRC was working on involved a 64-apartment building where all units were affected.

‘‘The owners will have to spend up to $2 million to fix this problem,’’ he said.

Unlike the cladding issue, which prompted government and insurance industry intervention because it involves newer buildings, owners of older apartmentswith legacy problems will have to shoulder the cost.

‘‘You could argue that magnesite is similar to the faultymaterials like flammable cladding, but because it’s not a new building, it’s been built at a lower standard in the old days, there’s no current pressure for the government,’’

Mr Johnsson said.

‘‘In those days, apartments were built quickly and builders didn’t take time to make the floors perfectly flat with the concrete.

‘‘The magnesite used to make the floors nice and flat was filled with sawdust and cork held together by a glue. Now the glue was the problem because it was made of magnesium oxychloride.’’

Magnesite absorbs water and dissolves the chloride in the topping.

Mr Marosszeky said the corrosion that occurs when the chloride leaches into the steel bars reinforcing the floor causes the concrete to expand by as much as eight times the volume of the original steel.

‘‘These expansive forces rupture the concrete, lifting the concrete just as a tree root lifts a footpath as the roots expand,’’ he said.

Magnesite damage could show up as hollow sound on tiles, cracking of tiles and bulging of the carpet over the rusting steel bars.

AFR magnesite story

Out of sight
Magnesite defects
Affected buildings Apartments built between 1960-1980
Registered strata buildings in NSW (1961-1979) 14,000 (186,000 units)
Cost to remediate Up to $100,000 per unit

Because of the slow corrosion, the symptoms aren’t visible until the damage is already widespread. ‘‘Usually, when it’s discovered, the affected area that you can see is nowhere near the extent, because it’s a massive hidden problem in the concrete,’’ according to Mr Johnsson. ‘‘So you’ll be looking at least two to three times the amount that is visible on the surface that will require repair. So when you see lumps on the floor, or corrosion rust stains on the concrete, the problem is already there.’’ Because it is a structural issue, ignoring it is not an option. ‘‘If you leave it for too long the bars simply get eaten away and then structural strengthening has to be undertaken, adding very significantly to the remedial cost,’’ Mr Marosszeky said. ‘‘If you let it go, it can cost more than $1000 per square metre to remediate the problem, so stay alert and get help as soon as you detect any issues. ‘‘In the worst cases, the building will collapse. You have to fix it because it’s a structural problem.’’