The development of water-based consolidants for Sydney sandstone in heritage buildings

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The work presented in this Thesis assesses the suitability and capacity of the aqueous consolidants designated for more compatible consolidation treatment of Sydney’s yellow block sandstone. The aqueous consolidant systems investigated included polymer consolidants, polymer-montmorillonite composite consolidants and in situ polymerisation consolidation. Polymer consolidants incorporating montmorillonite (MMT) were prepared by aqueous solution intercalation method and demonstrated the fast and efficient preparation of composites at the wide range of MMT concentrations from 2.5 to 90%, dispersed in the water soluble polyacrylic acid (PAA), polyacrylamide (PAm), or polyethylene glycol (PEG), or in situ polymerised PAm. While the intercalation behaviour, MMT dispersion, structural variations, intermolecular interactions between polymer and MMT and thermal stability were affected by the polymer-MMT ratios and the nature of polymers; the polymer-MMT ratios determined the trend in these changes, but the extent to which these occurred depended on the nature of polymers. PAA, PAm, PEG and in situ polymerised PAm produced the interlayer separation of MMT in the range of 13.1-19.6, 15.2-26.9, 14.2-19.7 and 20.3-28.1Å with the 50 to 60% MMT threshold incorporated into the polymer matrixes. The interlayer separation of MMT were similar for PAA and PEG, while PAm and the in situ polymerised PAm increased the interlayer expansion of MMT. The consolidant performance of PAA, PAm, PEG, the polymer-MMT composites and in situ polymerised PAA or PAm was compared with the commercial consolidants, hydrophobic Paraloid B67 (B67) and B72 (B72), water soluble Lascaux and the ethyl silicate Silres by their penetration ability, uptake, water vapour permeability, colour change and bending strength. The polymer-MMT ratio of the composite and the concentrations of polymer or monomer were critical. Practically, the composites containing less than 20% MMT were suitable and the polymerisation at greater than 10% Am or AA was unusable. Increasing the polymer concentrations reduced penetration, induced colour changes and reduced water vapour permeability. PAm and polymerised PAm showed the best performance, whereas PEG reduced mechanical strength and AA and PAA caused colour changes. In comparison, the hydrophobic commercial consolidants caused increased darkening and significantly reduced permeability although the water soluble Lascuax did provide some beneficial effect. The consolidants developed in this research represented mild consolidation action with minor changes in the characteristics of the treated sandstone. Encouraging results were observed for the performance of these water based polymer consolidants, in particular, PAm demonstrating the best consolidant of water based consolidation systems in the conservation of heritage sandstone.
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