Violeta Bokan Bosiljkov[1]
- Assistant Professor, University of Ljubljana, Faculty of Civil and Geodetic Engineering, SI- 1000 Ljubljana, Jamova 2, Slovenia, E-mail: vbokan@fagg.uni-lj.si
ABSTRACT
Various recent Restoration Charters recommend the use of lime-based mortars for the restoration of ancient European buildings because of their compatibility with the original masonry mortars, renders, plasters and bricks. The paper presents test results and experiences obtained with industrial and traditional lime putty-based mortars. The testing programme encompassed field studies of the behaviour of lime-based renders on the masonry walls made from solid clay bricks, and parallel tests of the characteristics of fresh and hardened limebased mortars. The tests were carried out on five lime-based mortar mixes: traditional limeputty:sand 1:3, industrial lime putty:sand 1:3, traditional lime-putty:sand 1:3 + 10% of metakaolin, industrial lime putty:sand 1:3 + 10% of cement and traditional lime-putty:sand 1:3 + 3% of polypropylene fibres.
The obtained results show that with mature traditional lime putty we can obtain lime mortar with superior properties in fresh and hardened state, compared to the lime mortar from industrial lime putty. The “traditional” lime render on the outside walls behaved very good and is after one winter still in the same condition. The use of plain lime mortar from industrial lime putty for rendering does not seem to be a very good decision, since this mortar needs too much water for good workability, which is a great drawback for the later process of the hardening. The addition of 10% of cement to the “industrial” lime mortar can improve some properties of the lime render in its “green” stage due to higher early strength of the render. On the basis of obtained results the addition of metakaolin to the lime mortars for rendering can not be recommended. The reason is wet spots on the render that are very unaesthetic and could also be harmful. In cases when higher ductility of the hardened lime renders is demanded, the incorporation of fine, flexible and evenly distributed fibres in the lime mortar could be a solution.
Key words: lime renders, lime-putty, additives, field studies, laboratory tests.
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