Maria do Rosário Veiga

Microstructural changes of lime putty during aging

AbstractThe microstructural development of lime putty is widely recognized and commonly associated with an increase in quality. Many heritage institutions encourage the systematic application of lime putties in conservation; however, all the issues associated with age are not fully understood. Changes occur during storage underwater, which traditionally took place in pits to prevent carbonation. The properties of mortars, plasters, and decorative finishes formed from lime putties are intimately linked to manufacturing parameters such as storage time. The hydration of calcium oxide was investigated using an environmental scanning electron microscope with particular attention to the nucleation of calcium hydroxide crystals on the surface of calcium oxide. Crystal modifications were monitored. The results obtained confirm and quantify the influence of slaking time in the microstructure of lime putties that is also reflected in the current referred special characteristics of the mortars produced with them, su...

Reapplication Mortars for Old Tiles: Characteristics of Tiles and Mortars and Selection Criteria

Glazed ceramic tiles have been used as facade claddings prominently since the beginning of the 19th century and they are today considered significant historic heritage. Several deterioration mechanisms threaten this important legacy. Detachment due to aging and to several external actions is one of the most dangerous mechanisms. New mortars compatible with the old tiles and old substrates are needed to reattach the loose tiles without deteriorating the glazed surface, the ceramic part, or the adjacent pieces. The tiles of the 19th century are very porous and absorbent, with variations according to the factory where they were produced. The adhesion of mortars to tiles is commanded by the penetration of the fine particles in the tiles pores, which depend on several composition factors. In this study, the characteristics of late 19th-century tiles are studied and compared with the characteristics of several types of new tiles and replicas. New mortars are formulated with the objective of reapplication of old tiles. The adhesion mechanism of substrate/mortar/tile system is analyzed and the factors involved are identified.

Adhesion of Air Lime-Based Mortars to Old Tiles: Moisture and Open Porosity Influence in Tile/Mortar Interfaces

The use of tiles in Portuguese facade coatings began in the nineteenth century with industrialized production of tiles. Nowadays, many nineteenth century facades are degraded and in urgent need of maintenance. New bonding mortars must be developed in order to substitute the existing ones. Compatibility, durability, and reversibility with the old materials must be respected. The tile/mortar adhesion strength is a very important characteristic in old tiles reattachment. It mostly depends on characteristics of mortars, porosity, and moisture content of tiles. Mortar in contact with a wet tile will have different binding characteristics than that in contact with a dry tile. This work studies the adhesion of lime-based mortars to old tiles and the influence of moisture and open porosity in the tile/mortar interface. New tiles with similar porous characteristics as nineteenth century tiles were used. A newly designed test was used to test the tile/mortar adhesion strength. The composition of mortars and moisture content of tiles was varied. Some trends of variation of mortar compositions and moisture conditions of tiles were observed in tile/mortar adhesion strength. The increase of moisture in tiles causes the increase of mortars’ open porosity. Mortars applied in wet tiles have higher values of adhesive strength than mortars applied in dry tiles. The tile/mortar adhesive strength increases with increasing open porosity of the mortar in the interface.

Conservation of Historic Renders and Plasters: From Laboratory to Site

In interventions on historic renders and plasters, the first step is to decide upon the strategy: repair or substitution, based on an evaluation of the cultural value of the render or plaster, of the building itself and on a careful diagnosis of the typology of defects, their quantity and reparability. New renders or repaired renders should fulfil the main functions they are required to, especially protection and aesthetic functions. Compatible materials should always be used. Compatibility is needed for durability, not of the render, but of the wall as a whole, and also for preserving the documentary and symbolic value of the building as well as its image. Compatibility is defined in relation to the substrate and the existing mortars. Therefore tests need to be carried out on the old materials and on possible solutions, to compare characteristics and assist in the selection of the best. It is acceptable to begin using non-destructive or slightly destructive in-situ tests, because with them it is possible to collect useful information quickly and without destruction of the historic renders. Simple mechanical and physical tests can be carried out on the old mortars and a few chemical tests can also be performed, with portable equipment. If rigorous and complete tests are needed, some samples can be collected and tested in the laboratory, using methods adapted to non-regular, possibly friable specimens. The characteristics of the mortars to use can be established, based on the results obtained, in order to fulfil both functionality and compatibility. However, sometimes it is not possible to obtain enough data about old materials, especially concerning masonry as a whole, which is more difficult to test than mortars. For this situation, some general requirements have been established, based on previous work carried out on Portuguese historic masonry buildings, which can be used without risk of damaging existing materials. Decisions concerning the materials to use, especially binder materials, should also take into account the climatic and environmental conditions. Appropriate application techniques, workmanship and curing conditions are indispensable in achieving good aesthetic, physical and mechanical results. Therefore it is important to know what conditions are available for the application phase. An effective knowledge of the historic materials and of the possible compatible solutions, of their characteristics and problems, is essential; tests are an important tool but the interpretation of their results in order to take useful decisions is a complex task, requiring a multidisciplinary team efficiently coordinated.

Characterisation of Decorative Portuguese Gypsum Plasters from the Nineteenth and Twentieth Centuries: The Case of the Bolsa Palace in Oporto

The use of gypsum plaster for the interior coating of walls and ceilings in the Portuguese architecture was particularly expressive in the period between the eighteenth and the twentieth century. However, information about this important heritage is almost nonexistent, which is leading to a rapid loss of important patrimony. In this paper the results of the characterisation of five gypsum plaster samples from the second half of the nineteenth century belonging to the Arabian Room of the Bolsa Palace, located in Oporto, North of Portugal, are presented and discussed. XRD and TGA-DTA techniques were used to establish the mineralogical composition, and the relative proportions of the binders. Optical microscopy and FESEM-EDS observations were performed both in fractured and polished surfaces in order to determine the stratigraphy and the composition of individual layers. The results of this characterisation work showed that the plasters used were mainly composed of gypsum and hydrated lime in different proportions – a feature that was correlated with the application techniques of the decorative elements analysed – and allowed the determining of the restoration interventions they had already been submitted to. Some physical properties like the dynamic modulus of elasticity and capillary absorption were also determined, and a correlation between the results obtained was established with previous studies performed by the authors.

Natural or Artificial? Multi-Analytical Study of a Scagliola from Estoi Palace Simulating Imperial Red Porphyry.

In this paper the characterization of a gypsum plaster sample from the end of the 19th century simulating imperial red porphyry using a multi-analytical approach is presented and discussed. The results of X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TGA-DTA), physical and mechanical properties are summarized. In order to have further insight into the microstructure, polarized light microscopy (PLM), scanning electron microscopy coupled with energy dispersive X-ray spectrometer (SEM-EDS), and micro Raman spectroscopy analyzes were also made. They helped to clarify the main issues raised by the other complementary analytical techniques and allowed the establishment of interrelations between the different properties, providing important information about the materials, the skills, and the technological development involved in the art of imitating noble stones with gypsum pastes. This study also contributes to our knowledge concerning the preservation of these types of elements that are important in the context of European decorative arts and rarely reported in the literature.

Mapping chemical disorder and ferroelectric distortions in the double perovskite compound Sr 2-x Gd x MnTiO6 by atomic resolution electron microscopy and spectroscopy.

In this work we report a study of the chemical and structural order of the double perovskite compound Sr 2-x Gd x MnTiO6 for compositions x=0, 0.25, 0.5, 0.75, and 1. A noticeable disorder at the B-site in the Mn and Ti sublattice is detected at the atomic scale by electron energy-loss spectroscopy for all x values, resulting in Mn-rich and Ti-rich regions. For x ≥ 0.75, the cubic unit cell doubles and lowers its symmetry because of structural rearrangements associated with a giant ferroelectric displacement of the perovskite B-site cation. We discuss this finding in the light of the large electroresistance observed in Sr 2-x Gd x MnTiO6, x ≥ 0.75.

Characterisation of Mortars Using Drilling Resistance Measurement System (DRMS): Tests on Field Panels Samples

Non-destructive or micro-destructive in situ tests are very relevant to the physical characterisation of materials used in historical buildings. “Controlled penetration,” “sphere shock” and “sonic methods” can be used to evaluate the mechanical resistance of mortars and renders or to monitor the hardening process after their application. Used to evaluate surface hardness, micro-drilling (DRMS) is a very sensitive technique, and its use in this field is expected to contribute to more precise results. However, the diversity of the composition of mortars and the systematic presence of abrasive components are limiting factors for the use of this method in this field. In this study, several mortars with different composition and hardness are compared using drilling resistance as the comparative parameter. The mortars were applied on-site aiming at their use in real situations. Extracted mortar samples were tested in the laboratory using resistance drilling which was complemented by additional methods currently used for in situ characterisation of these materials. The results highlight the need for an integrated perspective of laboratory and on-site information.

Effect of the Conservation Treatment of Historical Ceramic Tiles on the Tensile Adhesion Strength

The present work describes some preliminary results of a first attempt to study the effect of a conservation treatment on the adhesion strength of ancient ceramic tiles. Several tiles from the 16th through 20th centuries were submitted to a conservation treatment. The treatment involves the impregnation with Paraloid B-72 using a protocol widely used in most museum restoration departments. Treated and untreated tiles were attached to a brick surface with a bonding mortar. After 3 months, pull-off tests were performed in treated and untreated samples and the tensile adhesion strength was determined. Although a small number of samples was analyzed, the adhesion strength was found to increase for treated tiles in comparison with the pull-off strength of untreated samples.

Effects of the Incorporation of Waste Fibres on the Cracking Resistance of Mortars: A Review

The environmental awareness has prompted the construction industry to develop sustainable materials. Fibrereinforced composites are considered a pontential alternative to improve the durability of construction materials. These additions may also increase the deformation capacity and the energy absorption of the composite. Besides increasing the coating durability, recycled fibres may promote environmental gains. This paper presents a review of the researches done with recycled fibres, both synthetic and natural, and discusses fibre characteristics, properties and treatments to improve the performance of the composites. Therefore, considering previous studies, this work intends to analyse the incorporation of different kinds of recycled fibres to achieve better performance of cement mortars in terms of cracking resistance, impact strength and durability, without significant decrease in mechanical strength and water absorption. This article also intends to characterise the feasibility of the incorporation of waste fibres in cement mortars that could reduce their modulus of elasticity and increase their deformation capacity, to improve their resistance to cracking, based on previous works of the literature. The results suggest that the fibre incorporation provides an improvement in the cracking performance of the mortars. Parameters as length, type and treatment of the fibres are meaningful.