Magnesite: Key facts you ought to know

HERE is something of a blast from the past that’s cropped up in a couple of recent projects – magnesite.

Although it’s not commonly used anymore, the focus on refurbishing older buildings means contractors could well run across it, so it’s useful to be aware of how to deal with it.

Going back some 60 years or more, magnesite was a product used quite widely in flooring, especially for industrial premises as it was resistant to oil spillages. It’s a water-based product, usually reddish pink in colour, which was most commonly used as a floor finishing.

Magnesite is generally easy to spot because of its colour, although in some cases it was pigmented to other colours and so a quick way to check is to hold a small lump of the material to a gas flame. If it is magnesite it will glow brightly. There are some problems associated with magnesite, not least that due to its high conductivity it will give full damp scale readings on electric meters even when bone dry.

Crucially, because it is water soluble, magnesite will return to its previous state if exposed to enough water.
Magnesite is also flexible, meaning that it’s not suitable to be overlaid with a smoothing compound, and can’t be used with all types of floorcovering. A flexible covering such as carpet can be used, but problems are likely to occur with resilient coverings.

This means magnesite is a tricky material to work with for refurbishment and renovation jobs – especially those where a change of use is required.

For example, the popular procedure of converting older industrial buildings for commercial or residential use would generally mean some areas are laid with a resilient floorcovering, but these are not compatible with magnesite.

Further, although it was a popular material some years ago, times have changed and the introduction of more durable subfloor products has meant magnesite has fallen out of use.

So if you come across it, it’s likely to have been installed some years ago and showing signs of wear and tear.
The best option in these situations is to dig out the magnesite and lay a new floor. That’s clearly a time-consuming job, but removing it and then laying a damp proof membrane and a smoothing compound capable of offering a deep fill to replace the magnesite will mean the subfloor is much more suitable for modern use.

Taking into account the problems magnesite creates with floorcoverings, and the fact that it’s likely to be of a fair age and reaching the end of its useful life anyway, removal and replacement is the best option to get the job done right and avoid any repeat visits.

John Alcock is technical specifications manager at Bostik

www.bostik.com
T: 01785 272727