A ‘Sandwich’ Specimen Preparation and Testing Procedure for the Evaluation of Non-Structural Injection Grouts for the Re-Adhesion of Historic Plasters

ABSTRACT

Non-structural injection grouting aims to stabilise delaminated plaster by introducing in the void, typically between delaminated plaster layers, a compatible adhesive material with bulking properties (the injection grout). Injection grout formulations are firstly tested in the laboratory to determine their performance characteristics including their physical-mechanical compatibility with the original materials (plaster or other building materials). However, laboratory tests on grouts are often not sufficiently representative of actual cases in which the grout sets between two plaster layers. This problem is particularly significant when water vapour permeability, capillary water absorption and adhesion need to be assessed. A study was conducted on the development of a ‘sandwich’ system (plaster-grout-plaster) to better simulate the real situation. This paper describes a new methodology for such specimen preparation and the adapted procedures for laboratory testing. The results are discussed comparing them with those obtained from standard specimen preparation and testing procedure.

KEYWORDS:

• ‘Sandwich’ system
• injection grout
• adhesion
• capillary water absorption
• water vapour permeability
• plaster

Acknowledgments

The late Professor Sharon Cather had a profound impact on conservation worldwide. We are grateful for her guidance throughout this research. We would like to thank Dr Christian Paglia, Director of the Institute of Materials and Constructions (IMC, SUPSI), for access to the SUPSI-IMC laboratory to carry out the physical and mechanical tests. Samuel Antonietti (IMC, SUPSI), Head of the Laboratory, is acknowledged for his advice, together with the technical staff, Ezio Pesenti and Massimo Mezzetti. Many thanks are due to Beril Biçer-Şimşir (GCI) for her useful advice at the first stage of the research about ‘sandwich’ systems. Dr Bénédicte Rousset (CSC Sàrl) is gratefully acknowledged for sharing her knowledge and experience regarding the execution and interpretation of water vapour permeability and capillary absorption tests.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

¹ In an actual case, the situation is obviously more complex: more interfaces may be involved, the geometry may be not as regular, and so forth. Moreover, the layers of material to stabilise (in the scheme, generically ‘plaster’) are not necessarily the same.

² In such references cited, the results are expressed in water vapour resistance (μ) instead of water vapour permeability (δ). For easier reference, the water vapour resistance values of the materials tested in the present research are also reported here: plaster P has μ = 17; grout A has μ = 10.33, grout B has μ = 9, grout C has μ = 15.