Little did German chemist Johan Glauber realise the influence of the crystals he named Miracle Salt (Sol Mirablis). Not only would the material go on to become a major constituent of modern day soap powders, but it is also a vital constituent of glass manufacture and a “stepping stone” used in making a wide range of other industrial chemicals.

The chemical is known today as sodium sulfate (or sulphate for those of us old enough to remember real Bunsen burners and stained wooden bench tops in the chemistry lab).

Now, the miracle has become something of a curse when purchasing post WW2 properties built in former coal mining areas.

The problem has arisen as in late 1940's and 50's there was both was a chronic need for housing, and a shortage of imported wood to facilitate the suspended type floors that had been in vogue pre-war. The solution was to build up the under-floor with mining waste and to cap off with what was often a poorly specified and uncontrolled concrete.

The result thirty to forty years later has been that sulphate minerals both in the shale waste and un-burnt pieces of coal have dissolved in ground water and then re-precipitated as Glauber's miracle salt. Just like ice crystals in a frozen pipe these minerals punch well above their weight and have the capability of causing concrete floors to crack and heave, and in extreme situations can even cause external walls to shift on their foundations.

The only solution is to remove the old sub-floor and to replace with a non sulfate bearing hardcore: for example Leca® LWA insulation fill and top off with modern quality controlled concrete.

Our images show a property where leca® LWA has been used. The “before” images clearly show the offending red shale being excavated from the kitchen floor and later pieces of the shale and coal that have been collected and washed. Our "after" images show the ease with which 50ltr packs of Leca® LWA insulation fill can be installed.