Fast identification of the source of salt efflorescence by means of pH paper 1-14

The source of alkaline salt efflorescence (pH > 8) on monuments is always a building material (or restoration/conservation material) which is itself alkaline, such as cement, hydraulic lime or water glass (Schaffer, 1932 ; Arnold, 1985).

Therefore, if the measurement with a pH paper made on an efflorescence in situ or in laboratory gives an alkaline result (pH > 8), the search for the origin of the salts is very quickly orientated. On the contrary, if the pH is neutral or acid ( ≤ 8), the origin of the soluble salts can only be found after more sophisticated analyses and their origin could even be alkaline materials as the ones mentioned above.

In situ measurement: 
– humidify the pH paper
– hold it into the efflorescence or frict on it
– read the value
Laboratory measurement:
– dissolve the salts in a drop of water
– hold the pH paper into the drop
– read the value

Arnold, A. (1985). « Moderne alkalische Baustoffe und die Probleme bei der Konservierung von Denkmälern. » Natursteinkonservierung, Arbeitshefte des Bayerischen Landesamtes für Denkmalpflege, 31, 152-162.  

Schaffer, R. J. (1932). « The Weathering of Natural Building Stones. » Facsimile of the 1932 edition , published by Construction Research communications Ltd, by permission of Building Research Establishment Ltd.