Cement Render and Mortar and Their Damages Due to Salt Crystallization in the Holy Trinity Church, Dominicans Monastery in Cracow, Poland

Mariola Marszałek,Adam Gaweł,Krzysztof Dudek

doi:10.3390/min10070641

Abstract

The investigations focused on the façade of the 17th-century Myszkowskis chapel at the 13th-century Church of the Holy Trinity in Cracow, Poland. Most of the chapel’s façade is made of rusticated limestone blocks, but its lower part is covered with cement render, and the basement consists of irregular pieces of limestone and sandstone, bound and partly replaced with cement mortar. The façade exhibited clearly visible damages: gray soiling of the surface, cracks, scaling, and efflorescence. The study presents characteristics of the cement render and mortar used for stone repair and/or substitution, as well as efflorescence from the lower part of the Myszkowskis chapel façade. The materials were analyzed with optical microscopy, scanning electron microscopy (SEM-EDS), Raman microspectroscopy, X-ray diffractometry (XRPD), and mercury intrusion porosimetry. The analyses demonstrated that the render covering some of the decayed limestone blocks was prepared using Portland cement (residual clinker grains represent alite and belite) as a binding agent, mixed with crushed stone as an aggregate. The cement mortar consisted of rounded quartz grains, rock fragments, and feldspars in very fine-grained masses of calcite and gypsum, also containing relics of cement clinker (alite, belite, ferrite, and aluminate). All these components point out the use of the ordinary Portland cement. Analyses of the efflorescence allowed us to distinguish several secondary salts, among others, thenardite, aphthitalite, and darapskite. The appearance of these phases is related to the composition and physicochemical properties of the building materials, atmospheric alteration agents, air pollution, and some other anthropogenic factors.

Highlights

Construction mortars consist of various inorganic or organic binding materials and natural or artificial aggregates with or without pigments
Samples selected for the studies represent two types of the building materials taken from the Myszkowskis Chapel façade and subwall, as shown in Figure 1: a piece of the wall in places covered and/or filled with bright cement render, above the pavement level, and the cement mortar between stony blocks in the subwall below the pavement level
The petrographic characteristics of the materials were based on analysis of thin sections cut perpendicularly to the outer layers of the samples, using an Olympus BX-51 instrument coupled with an Olympus DP-12 digital camera (Olympus Corporation, Tokyo, Japan)

Summary

Introduction

Construction mortars consist of various inorganic or organic binding materials and natural or artificial aggregates with or without pigments. Inorganic binders may be lime, cement, silica gel, or gypsum, and organic ones can be animal glue, polyester, acrylic or epoxy resins, whereas aggregates are most often sand or gravel. The kind of binder depends on the application area, climatic conditions and, in particular, on the moisture transport and mechanical properties of stones. Inorganic or organic additives are often used to adapt the mortar properties to the stone and to improve its durability. RC is still in use in conservation because the restoration of historic masonry requires materials with physico-chemical and mechanical properties similar to the original ones [2,3,4,5,6]

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