Abstract
The perceived increasing use of ‘restoration mortars’ for the conservation of historic masonry is often viewed as controversial due to the long-standing contention associated with ‘plastic’ repairs in the heritage sector. Almost innumerable traditionally built sandstone structures exist worldwide and the wide scale use of restoration mortars for their repair is evident on a national and international level. Use of largely incompatible, impermeable and/or highly cementitious materials in the past is the cause of many problems, particularly associated with moisture entrapment. These issues, that continue several decades after a material’s use, raise the question of whether similar problems are likely to arise in the future due to the use of restoration mortars. The chemical and physical characteristics of two restoration mortars are determined by laboratory testing. This work revealed significant differences in the physical properties of two restoration mortar materials, but also between these and the physical properties of two natural sandstones. Material characterisation reveals differences between the composition of the binders and aggregates in the two restoration mortars tested. Significant differences in their strength and water diffusion properties were noted. The results provide an indication of material performance and a platform for objective decision-making on the suitability and specification of these materials. This work is of particular importance in the heritage sector, but its applicability is not limited to historic buildings. Comparison of the materials properties presented in this paper with the characteristics of representative sandstone substrates can give an indication of material compatibility. This research is aimed at stimulating further testing into the interactions of these materials within the context of historic masonry substrates.
Highlights
The perceived increasing use of ‘restoration mortars’ for the conservation of historic masonry is often viewed as controversial due to the long-standing contention associated with ‘plastic’ repairs in the heritage sector
Astier (CESA), France) and Conserv (Stone Tech (Cleveland) UK). The former has been highlighted in another study [2] as a popular stone repair material in Scotland its inclusion in this study, and the latter was selected based on its diffusivity and availability within the UK via established supply chain and pronounced merchant outlets
The absence of portlandite in the anhydrous Lithomex may be associated with the qualitative nature of X-Ray diffraction (XRD) technique
Summary
The perceived increasing use of ‘restoration mortars’ for the conservation of historic masonry is often viewed as controversial due to the long-standing contention associated with ‘plastic’ repairs in the heritage sector. Impermeable and/or highly cementitious materials in the past is the cause of many problems, associated with moisture entrapment These issues, that continue several decades after a material’s use, raise the question of whether similar problems are likely to arise in the future due to the use of restoration mortars. Plastic repair using a restoration mortar is one popular method used for the treatment of a number of different building elements [2]; the word ‘plastic’ denotes the in entrapment of moisture This can lead to accelerated deterioration of masonry due to mechanisms such as freeze-thaw cycling and salt sub-florescence [6,8,9,10,11]. This knowledge and experience has led to the reintroduction of lime (Table 1) as a repair material for building conservation work
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