Estimation of the linseed oil content in historic lime mortar

Vegetable oils (e.g. linseed or tung) were used as lime mortar admixtures in order to increase the mortar durability (due to the water repealing effect) and/or to prolong the mortar's workability. The present paper aims to investigate the possibilities of thermal analysis to estimate the linseed oil content in a historic mortar. A set of model mortars containing Ca(OH)(2), CaCO3 and variable amount of linseed oil was studied by methods usually used for mortars characterization: thermogravimetry with evolved gas analysis by mass spectroscopy (TG EGA-MS), FTIR spectroscopy (Fourier transform infrared spectroscopy) and XRD (powder X-ray diffraction). Oil admixed in lime mortar undergoes two principal transformations: saponification to Ca carboxylates and polymerization (drying). The products of the oil transformation are thermally decomposing during the thermal analysis experiment, but unfortunately in the same temperature range as Ca(OH)(2)-common mortar component-does. A calculation procedure which enables to determine content of both Ca(OH)(2) and oil products on base of thermogravimetry was proposed. As an alternative, an estimation of oil content based on EGA-MS results for m/z 95 ion was developed. Finally, total organic carbon (TOC) may be also used if any other organics are not present. These three approaches were used for the oil content estimation in the sample of historic mosaic mortar. The result obtained by TG EGA-MS approach was found to be the most realistic.

Automated summary

This paper investigates the possibility of using thermal analysis to estimate the linseed oil content in historic mortar. By studying model mortar samples, a calculation method and mass spectroscopy analysis were proposed to determine the oil content, and it was found that the mass spectroscopy analysis method yielded the most accurate results.