Salt crystallization in plastered or rendered walls
Este registo pertence ao Repositório CientÃfico do LNECThis thesis was aimed at understanding the behaviour of plasters and renders on salt-loaded
walls. The current state-of-the-art and state-of-the-practice were accessed focusing
particularly on old plastered/rendered buildings and their conservation practice in Portugal.
Afterwards, experimental work was carried out aiming at answering the identified questions.
Two laboratory techniques, for relative humidity control with salt solutions and for salt content determination by hygroscopic moisture content measurements, were investigated. Drying of salt-loaded materials was studied by means of drying experiments monitored using a magnetic resonance imaging (MRI) technique. The behaviour of plasters and renders in
relation to salt crystallization was then accessed by means of crystallization tests and
MRI-monitored drying tests. Most drying and crystallization tests were carried out on
specimens composed by a plaster or render applied on a given substrate. Finally, the study of five old buildings in Portugal provided an insight into practice-related salt decay features.
On the basis of this research, guidelines are proposed to select plasters and renders for salt loaded walls. Conclusions were also achieved on: (i) possibilities and limitations of the test
methods, particularly salt crystallization tests, and diagnostic methodology used;
(ii) salt decay processes, namely, influence of soluble salts on drying, mechanisms of
salt-induced dampness and salt distribution in masonry; (iii) reasons for sodium chloride being typically much less damaging than sodium sulfate in laboratory tests; (iv) influence of factors such as the type of salt, kind of substrate material or presence of a paint layer on the
behaviour of plasters and renders; (v) factors that can account for a worsening of salt damage after restoration interventions; (vi) field or application conditions that favour salt damage.This thesis was carried out at the National Laboratory for Civil Engineering (LNEC), in
Lisbon, partially within the framework of two research projects: the European project
“COMPASS – Compatibility of plasters and renders with salt loaded substrates in historic buildingsâ€, and the national project FCT/LNEC “Metodologias para a mitigação do risco associado à degradação das construções (Methodologies for the mitigation of risks associated with the degradation of constructions)â€. The use of magnetic resonance imaging was carried out at the Centre for Material Research with Magnetic Resonance in Eindhoven University of Technology (TUE).13844262IST / Universidade de LisboaDM/NPC
http://www-ext.lnec.pt/LNEC/bibliografia/DM/TG_PhDthesisMar2008.pdf