TAN 19 S C ~ I SAGGREGATES H FOR BUILDING CONSERVATION
Q Figure 15 Decrease (1995, page 135).
4 i11
8 12 16 20 24 Moisture Content of Sand-per cent
true vollmw of sand due to bulking (for a constant vol~imeof moist sand). Takenfrom Neville
mix is required. If a damp sand occupies lOOOml (1 litre) in a measuring cylinder, and excess water is added, the volume should become approximately 800ml after some agitation to remove trapped air. This gives a bulking ratio of twenty per cent, or a bulking factor of 1.25. In practice, ignoring the bulking effect of damp sand will result in a slight increase in the lime content of the mortar.
3.02
28
Mortar analysis and interpretation
Traditional mortars consist of a mixture of carbonated, and 1 or set hydraulic, lime and aggregate, with possible additional constituents such as clay, gypsum, cementitious materials and reinforcing fibres in the form of animal hair or other fibrous materials. Small quantities of other organic substances may also be present. Mortars and their constituents can be analysed in a variety of ways ranging from formal laboratory procedures in accordance with British Standards documents 8901 6463 and EN 4597to and qualitative evaluation. The laboratory based tests are designed primarily for modem cementitious mortars but can, in some circumstances, provide useful backup in the evaluation of lime mortars. Other potential analysis methods include x-ray analysis techniques (to identify the presence of various elements and minerals); examination of thin and polished sections, and other visual and microscopic examinations; and simple acid dissolution and aggregate quantification. Methods can also be employed to identify, for example, traces of organic materials.
The main reasons for the analysis of historic, and other, mortars are to provide a reasonably accurate estimate of the original constituents and their relative proportions,
.
in order that a matching or compatible mix can be identified, to aid the understanding of traditional methods of production and use of historic mortars, to enable comparisons to be made between various parts of a historic building as an aid to establishing the sequence of construction or alteration, to provide an accurate detailed record, for research or archive purposes, of the constituents of an historic mortar, and to investigate mortar constituents and curing in the event of problems being encountered with a new lime based mortar.
The methods of investigation chosen will normally relate to the reasons for analysis. In most instances, and particularly where the purpose of the analysis is to assist in the specification of a matching or compatible mix, it is common practice to start with a detailed visual evaluation and simple analysis through the dissolution of the lime binder using acid. This will and its provide information on the nature of the probable original method of production; on the type of lime, or other binder, used; on the type and characteristics of the aggregate and on the relative proportions of the various constituents. Analysis using acid dissolution is a method that is particularly suited to the examination of Scottish mortars (Leslie & Gibbons 1999), which do not commonly contain limestone or shell aggregate. For the purposes of identifying a compatible repair mortar, information on the type of lime, on the relative proportions of lime and aggregate and on probable production methods can form the basis of a specification, and information on the aggregate component of the mortar can be matched to information held in the database to identify a suitable, if possible, local, source of aggregate. In cases where a