Spalling....

... back in Edinburgh. Long day - not eased by a three hour Skype meeting with London!

I'm not 107 years old - it just feels like that. But the house is. Why does good solid stonework survive that long and then decide to spall? Well - here is the probable cause.

Salt crystallisation, where salts within the stone are drawn to the surface by the process of wetting and drying, where they crystallise can be very damaging. If the pore structure of the stone is unable to accommodate the resulting expansion, the surface of the stone can disintigrate. Frost action is probably the next most damaging occurence, followed by the action of organisms such as algaes and lichens and plants such as ivy. Air pollutants, are no longer such a problem following the clean air acts.

May take a few more hours before normal commenting....