In situ assessment of the stone conservation state by its water absorbing behaviour: a hands-on methodology

This paper describes the use of the water absorbing behaviour (WAB) for assessment of the conservation state of stone in situ. A test methodology, consisting of a combination of techniques for in situ measurement of the WAB, was applied in a case study on Lede stone, a sandy limestone, used in a medieval facade in Ghent, Belgium. The methods used were the contact sponge method (CSM), the Karsten tube (KT) and the droplet method (DM). Additionally, the residual hardness of the stone was measured by Schmidt hammer (SH). After careful selection of representative measuring points, a qualitative analysis of the stone's condition could be made, based on its WAB, residual hardness, reference data from laboratory experiments and thorough visual observations. From this analysis it could be concluded that CSM, KT and SH generated coherent and compatible results; that DM could indicate superficial alterations which were not necessarily representative for the subsuperficial WAB and that this methodology could give an insight on the conservation state, beyond visual observations, when combined with reference data.