Innovative Water-Reduced Injection Grouts for the Stabilisation of Wall Paintings in the Hadi Rani Mahal, Nagaur, India: Design, Testing and Implementation

ABSTRACT

The design and evaluation of site-specific injection grouts for the stabilisation of delaminated wall paintings is often challenging to perform in situ, due to constraints such as time, availability of materials and reliable testing procedures. In this research, a rigorous design and testing methodology, including the development of a new adhesion test, was adopted on-site for the development of injection grouts to be used in water-sensitive situations. Water-reduced mixtures were obtained by partly substituting water with ethanol. Previous research by the authors had demonstrated in the laboratory the potential suitability of water–ethanol grouts. In the present paper, water-reduced grouts were designed, tested and applied on-site for the first time.

KEYWORDS:

• Injection grout
• design
• field testing
• water-reduced
• ethanol

Acknowledgements

The Courtauld Institute of Art has worked to preserve the wall paintings of the Ahhichatragarh fort and palace complex of Nagaur since 2005, in partnership with the Mehrangarh Museum Trust. We are grateful to the Leon Levy Foundation who supported the project at the Hadi Rani Mahal. The late Prof. Sharon Cather had a profound impact on conservation worldwide, and we are grateful to her and to Prof. David Park for their guidance in the conservation project at the fort of Nagaur. Thanks are due to Sarah-Jane Fox and Yang Chen for the testing carried out on grout MG. We would like to thank Dr Christian Paglia for access to the laboratory of the Institute of Materials and Constructions (IMC) at the University of Applied Sciences and Arts of Southern Switzerland (SUPSI) to carry out the porosity test.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Notes

1 This Rajasthani technique, which flourished in the nineteenth century, includes from two to five plaster layers; the araish plaster is the final polished layer. Lime and brick aggregates (surkhi) are present in the intermediate layer, lime, brick and sand aggregates in the bottom layer(s) applied onto the masonry. Organic additives are present throughout (Courtauld Institute of Art 2016, 311); see also http://www.unescobkk.org/fr/culture/wh/asia-pacific-heritage-awards/previous-heritage-awards-2000-2013/2000/technical-brief/araish/, consulted on 17 April 2020. The tradition is orally transmitted from mason to mason, therefore, variations in the technique and in the preparation of the plasters may be encountered.

2 Porosity was tested in the laboratories of the Institute of Materials and Constructions of the University of Applied Sciences and Arts of Southern Switzerland (SUPSI), following the standard SIA 262/1:2003. The control grout (without aluminium powder) has the following porosity: n = 44.39%, U_E = 37.53%, LP = 6.86%, where n is total porosity, U_E is capillary porosity and LP is air pores percentage. The same grout with addition of aluminium powder (0.15% w/V, weight to the total volume of the grout) has the following porosity: n = 52.63%, U_E = 37.41%, LP = 15.22%, resulting in an overall higher porosity, with an air pores percentage ca. 8 percentage points higher than the one of the control.

3 The 2% expansion was desired for grout G for the following reason: grouts without expansion showed shrinkage (exacerbated by the dry ambient environment) and therefore poor adhesion; considering the thickness of the delamination and the amount of material to be injected, expansion was sought to counteract shrinkage. This was not necessary for grout MG, which was not visibly shrinking in the thin thickness it needed to address, therefore expansion was judged not to be crucial. 2% has been identified as an adequate expansion to counteract shrinkage and small enough not to lead to mechanical tension.

4 The clay used was Pangel^® S9 (supplier: Tolsa), which is composed of highly purified sepiolite, micronised to provide high pseudoplasticity; such clay is stable at high electrolyte concentration, therefore in presence of high amount of soluble salts (https://adhesives.specialchem.com/product/a-tolsa-pangel-s9?flag=1, consulted on 17 April 2020).