Jan Válek

Historic Mortars: Characterisation, Assessment and Repair. A State-of-the-Art Summary

One hundred and forty-eight original contributions on historic mortars and related subjects were presented at the 2nd Historic mortars conference, which took place in Prague September 22–24, 2010. The papers presented the latest research topics and advancements in this field. The editors vigorously reviewed the papers and selected 34 original contributions to be published in this special post conference publication. These papers constitute the essence of the current State-of-the-Art of research on historic mortars. The summary of these papers is put into a wider context of the past research, current practice and pre-normative activities of RILEM Technical Committees on characterisation of historic mortars (TC 167COM and TC 203RHM).

Experimental Study of Hot Mixed Mortars in Comparison with Lime Putty and Hydrate Mortars

An experiment was carried out in order to understand the influence of hot mixing on the properties of hardened mortars in comparison with mortars made of lime hydrate and lime putty. Lime from the same quarry and producer was used in the form of lime hydrate, lime putty and quicklime. Two types of quicklime were used, varying in their calcination conditions and also their reactivity. Standard specimens of 40 × 40 × 160 mm were cast and evaluated after curing. Mechanical (compressive and flexural strength) and physical properties (open porosity, bulk density, capillary absorption) were determined on the specimens of hardened mortars. Thin sections of the mortars were prepared and evaluated using polarising microscopy in order to describe the structure of mortar including the presence of binder related particles. The produced hot mixed mortars had hardened properties comparable with the lime putty and lime hydrate mortars. Due to the micro-cracks in the binding matrix the hot mixed mortars showed higher porosity and capillary absorption. The heterogeneity of the hot mixed mortars was a result of the preparation technology.

Reconstruction of a Baroque Open Beam Ceiling Based on Material Analysis

Reconstruction of a ceiling in the north-eastern wing of a former water fortress in Jeseník was carried out during the repair of its roof structure and replacement of the roof. The most damaged parts of the bearing ceiling beams were removed and partially replaced with new timber in the 70s of the 20th C. The way the work was carried out corresponded to the methods and approaches of the cultural heritage protection of that time. The replacement of damaged heads of ceiling beams with new timber that was fitted without connection to the original ceiling beams and only simply hanged on a metal girder can be considered highly provisional from the current perspective. That is why the repair of timber structures of the water fortress included also a reconstruction of the original ceiling system. Surveys focusing on the building archaeology and material assessing the condition of the incorporated timber were important for the final design of the repair and the concept of presentation of the Baroque ceilings.