The effects of commercial chemical cleaning processes on sandstones in Scotland.

This research programme investigated the effects of commercial chemical cleaning processes on sandstones in Scotland. The work follows a logical path from an understanding of the materials, both the stones and the chemical cleaners, involved. There is a great variation in sandstone types commonly used in buildings in Scotland, and of the 24 available freshly quarried stones 7 were chosen for wide ranging study. In addition a great variety in methods of cleaning are available. Current commercial cleaning processes are reviewed in a critical account of both physical and chemical cleaning methods. The chemical cleaning methods were grouped according to their physical and chemical properties. Four representative cleaning methods were chosen for use in standardised laboratory cleaning regimes. The sandstone and the resultant effluent liquids were monitored throughout each process building up a data base of information. The initial work was carried out on freshly quarried sandstone, this eliminated matrix effects that could be caused by a polluted weathered surface. The techniques developed were then applied in the field where the some significant differences from the laboratory studies on freshly quarried stone were found. The cleaning of polluted weathered stone in the laboratory, where stricter methods of control were adhered to, revealed that this difference was in fact due to the presence of sulphate probably from atmospheric pollution. On scrutiny of the data base constructed from the results of the above studies practical conclusions were drawn: 1) That sandstone can absorb and retain applied chemicals. 2) That sulphate content of polluted stone may play a significant part in determining the fate of chemicals applied to the stone surface. 3) Chemical processes whether acid or alkali based, attack the silica-based constituent minerals in sandstones at some stage in their use, changing both the physical and chemical nature of the affected stone. 4) The mechanism of the cleaning process may be by dissolution of the stone from beneath the dirt. 5) Diffusion of soluble ions and capillary action may both play an important role in determining the fate of chemicals applied to the stone surface. 6) That stone minerals, such as clays have little influence on the equilibrium position in the reaction between soluble sulphate and sodium hydroxide; at the concentrations used in commercial practice. The techniques developed in the course of this research have since been successfully used to study the effects of cleaning on a prominent public monument in Edinburgh. As part of the conclusion of this study a set of recommended test procedures to be carried out prior to cleaning a sandstone building or monument has been described. These will become the basis of Historic Scotland's own test procedures to be published in a practitioners' guide.

Grantor dc:publisher.institution

Robert Gordon University

Year dc:date.issued

1993

Author dc:creator

• MacDonald, John

Advisor dc:contributor.advisor

• K. Tonge

• Sandstone cleaning
• Chemical cleaning processes
• Stone-chemical interactions
• Sulphate contamination
• Stone deterioration
• Scotland

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:2807469
https://doi.org/10.48526/rgu-wt-2807469

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:2807469