Changes are usually made only where the existing materials have been shown to be inappropriate.In recent decades, specialists involved in the conservation and repair of historic buildings have become increasingly concerned by the damage caused by the use of certain types of mortar on historic brick and stonework, and by the use of ordinary Portland cement in particular.Instrumental techniques for the analysis of component materials - Scanning electron microscopy (SEM); electron microscopy with x-ray analysis (SEM/EDX); and x-ray diffraction (XRD) SEM high resolution images of the surface of samples with magnification of up to 100,000x show the structure of the mortar.
Data from the testing of complex materials is difficult to interpret, and a highly skilled analyst is crucial.
However, a better understanding of historic mortars is clearly required, not least because there have been some cases where modern lime renders have failed and, at the opposite extreme, there is now concern as some types of modern hydraulic lime mortars continue to gain strength as they age.
In parallel with the conservation industry, mortar analysis has progressed dramatically over the last 20 years.
Instrumental techniques for the analysis of organic materials - Gas chromatography with mass spectrometry; ion, liquid and thin layer chromatography These techniques are used (although rarely in mortars) for the identification of oils, resins, and proteins.
Instrumental methods for characterisation of organic and inorganic materials - Thermal analysis (DTA, TGA, DSC) and infra-red spectroscopy (FTIR) Thermal analysis can be carried out on very small samples and can positively identify the composition of certain components, including calcium carbonate, calcium hydroxide, calcium sulphate, calcium silicate hydrates, and depending upon the constituents remaining after ageing, complex calcium silicate and aluminate hydrates.
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Generally these tests consisted of dissolving a sample in dilute acid to separate the acid-soluble from the insoluble.