Identification of stone, cement and lime based materials using scientific analysis available at the University of Lincoln for buildings conservation projects where the specification and replication of historic materials is required.
When repairing historic buildings, it is important to understand the nature of its early renders, mortar and plasters. This ensures that compatible materials are used, essentially on a like for like basis providing optimum performance in terms of colour, texture, compressive strength and overall characteristics. The new mortar will then behave in the same manner as the old, continuing to weather and age seamlessly, helping to maintain the aesthetic quality of the building and preserve its structural integrity.
Samples are first ground to an even powder for a simple visual analysis under an optical microscope, with the powder sieved and the binder separated from the aggregate. Both aggregate and binder are analysed in triplicate by powder X-ray diffraction to determine the mineral phases present. This identifies the binder type (e.g. lime, hydraulic lime, Portland cement etc) and aggregate type (e.g. siliceous sand, calcitic sand etc).
A fully illustrated report is issued upon completion, indicating the following:
- Aggregate: Binder ratios by weight and volume.
- Aggregate and binder grain sizes.
- All mineral phases present (binder and aggregate)
- Summary of observations and conclusions outlining the make-up of the historic material
Optional additional analysis
Mechanical and physical testing
- Compressive strength, tensile strength, flexural strength using an Instron Universal Testing Machine;
- Moisture permeability.
Soluble salt quantification
- A portion of the sample (~0.5 g) is weighed accurately and placed in a vial.
- Deionised water (10ml) is added to the vial and the vial sealed.
- The sample is shaken and left to stand overnight.
- Each sample is then decanted, leaving the solid residue in the vial and filtered (0.45µm).
- A series of appropriate standards are prepared for calibration.
- Standards and samples are analysed by ion chromatography (IC) using a DIONEX ICS-1000. Both cations and anions are quantified.
- Simple results report issued.