In this doctoral thesis the development of compatible injection grouts based on hydrated lime for non-structural consolidation of detached plaster layers of decorative architectural surfaces (mural paintings) is studied. A review of Slovenian and international conservation practices of re-attachment interventions of historical plaster layers is given, which has resulted in well-defined requirements for injection grouts that must be compatible with historical renderings in the chemical, physical and mechanical aspects. At the same time, the injection grouts had to assure good working properties in the fresh state, evaluated according properties such as fluidity, injectability, water retention, minimal shrinkage, stability, etc. Injection grouts were developed in several phases. In the framework of preliminary research 9 different injection grouts were designed. Volume stability of the injection grouts was selected as a criterion for the selection of compositions used for further researches (17 injection grouts). Injection grouts were designed based on mineral binder and filler (hydrated lime and inert limestone filler), ultra light filler (for weight reduction), tuff as puccolan additive (to increase the mechanical properties) and chemical admixture (PCE and PPh superplasticizers) to reduce the water content. The first selected measure to increase the volumetric stability of grout mixtures was the decrease of the binder to filler ratio. The second measure was the use of superplasticizer to reduce the water content for the required workability. Furthermore, the research of grout mixtures was divided into several steps by eliminating the mixtures with poor properties (not reaching the requirements). In the framework of the research work, special models have been developed – models with air pockets and sandwiches simulating the detached plaster layers and allowing additional research of significant properties, such as adhesive strength. The grout mixtures were tested following the modified standard tests specially adapted for non-structural grouts. Grout mixtures L1 S3 PCE and L1 S2B1 PCE have proved to possess the most optimal combinations of key properties. Both mixtures have good volumetric stability with minimal shrinkage, and good water retention and injectability with dry and pre–wetted crushed lime mortar columns. Their mechanical and physical properties are within the range of historical plasters and provide good adhesion in the case of 2 mm high air pockets. Moreover, accelerated ageing showed that mixture L1 S2B1 PCE is more durable under various climatic influences in combination with distilled water or NaCl. Therefore, mixture L1 S2B1 PCE was selected for stabilizing the detached plaster layers of the selected mural painting.
|
