De Clercq, H. and Godts, S. (2014). Salt extractions of brickwork: a standard procedure? Hilde De Clercq (Ed.) SWBSS2014, Proceedings of the Third International Conference on Salt Weathering of Buildings and Stone Sculptures, Brussels, 14-16 October (original) (raw)

Salt extractions of brickwork: a standard procedure?

Crystallization of salts is recognized as a major factor in the degradation of porous materials in built heritage. Salt damage occurs in the presence of salts and moisture, in liquid or vapour form. This implies that, in case one of both can be excluded, salt damage can be mitigated. A salt extraction aims to reduce a maximum amount of salts present. In practice salt extractions are often executed without scientific background or control of its effect or durability.This paper deals with the results of salt extractions using a poultice consisting of a mixture of kaolin, sand and cellulose fibers applied on salt contaminated brickwork of two cases, the abandoned coal mine site named C-mine in Winterslag and two chapels of the Cathedral of Our Lady in Antwerp. Results have shown that several factors influence the salt extraction effect: the amount and distribution of salts, the pre-wetting properties, the physical properties of the building materials as well as the environmental condit...

Salt extraction by poulticing in the archaeological site of Coudenberg

A common method for the extraction of salts is the use of poultice materials. Despite extensive scientific research, the salt extraction process in practice often remains empiric. This paper aims to further the understanding of a salt extraction by poulticing in practical experiments. Three types of poultice materials are tested on brick masonry in 12 different locations in the subterranean archaeological site of Coudenberg in Brussels. The tested poultice materials have different compositions including kaolin clay, sand and/or cellulose fibres, theoretically favouring advection and/or diffusion. It is shown that for an accurate interpretation of the results it is crucial to evaluate the salt content in the poultice and to a depth of at least 20 cm in the different materials of the substrate, while considering the different densities and surface area of each material. Furthermore, it is shown that the presence of gypsum overshadows the results, hence the exclusion of equimolair contents of Ca2+ and SO4 2- is essential for the evaluation. Finally, the results of these experiments reveal that regardless of the different procedures, such as, the poultice type, pre-wetting or application time, salts are being redistributed into the wall rather than extracted.

Damage development to treated brick masonry in a long-term salt crystallisation test

Construction and Building Materials, 2004

The development of salt-damage to brick masonry specimens, treated with a water repellent and a consolidant, during a longterm salt crystallisation test, is evaluated. The experiment performed followed the Recommendation RILEM TC 127-MS-A.1, which uses constant drying conditions 20 8Cy50% RH. Due to the fact that the specimens on which, the salt crystallisation test was performed has been stored for several years under the same test conditions, repeated evaluations could be performed over time. The treatments comprised a water repellent (siloxane), a consolidant (ethyl silicate), as well as a treatment of ethyl silicate followed by siloxane. Three months was initially considered to be the end of the test, being the period in which the specimens could dry out almost completely. The damage present after 4 days, 3 months and 48 months has been compared. It was found that in the period between 3 and 48 months the damage mechanism still goes on, although nearly all water introduced as a salt solution at the start of the test had evaporated. Most damage indeed occurred in the period approximately between 12 and 48 months.

Quantification of salts in extracts from bricks ('wall of bricks' at the Wawel Castle in Cracow)

1999

The concentration of soluble salts in the retaining wall of the Wawel Castle was estimated. This wall bears the pressure of a steep, earthen slope of medieval fortifications. The analyses have shown that the samples contain mainly sulphate, nitrate, chloride, calcium, sodium and potassium. The concentration of the ions increases distinctly from the inner side of the wall toward the outer, exposed part. Due to the specific position of the wall and in contrast to most other buildings, water penetrates the retaining wall from the side abutting the scarp, while capillary suction from the foundations is of minor importance.

Characterisation of the progression of salts in walls of earthen architecture heritage

Mineralogical Magazine, 2022

Two hundred years (1750-1950) of earthen architecture represents an important period of construction in the central region of Portugal. Earthen architecture is usually built close to the coast or to rivers and placed in sandy ground. The impact of rising damp is a general problem and efflorescences are a common cause of damage decay. This problem was studied in a building with two types of earthen construction, adobe masonry walls and formed masonry walls. The aim of this research was to characterise the conditions for the appearance and phase transitions of thénardite and mirabilite, and determine how to prevent progression of salt effects in the two types of wall to support future conservation measures. Laboratory capillarity and porosimetry tests with dolomitic air lime mortar and hygrothermal monitoring were pursued along with in situ tests. Visual assessment showed that the progression of salts depends on the composition of the earthen materials. To understand these differences, all crystalline solid phases were analysed by powder X-ray diffraction, and building interior hygrothermal conditions were monitored. An investigation into the influence of surface lime water painting and sacrificial mortar application on the crystallisation of sodium sulfates concluded that these also depend on the wall's composition. Data allowed us to conclude that inside the building the temperature and humidity [relative humidity (RH = 100 p w /p°w > 70)] conditions led to the adobe breakdown by the fast conversion from thénardite to mirabilite. Therefore, contact with wet atmospheres should be avoided and interior hygrothermal conditions should be controlled. Laboratory and in situ tests showed that the environmental conditions of the spaces had effects on the results. The results contribute to understanding of the salt progression and pattern of decay, as well as supporting future recommendations for building conservation, based on the identification of environmental conditions proper to their occurrence.