Diethyl Oxalate-based Microgrouts in Calcium Carbonate Systems: Formulation and Application Parameters Jennifer Herrick Porter a , C. Pasian a , and M. Secco b,c a Department of Conservation and Built Heritage, University of Malta, Msida, Malta; b Department of Cultural Heritage (DBC), University of Padua, Padua, Italy; c Inter-Departmental Research Center for the Study of Cement Materials and Hydraulic Binders (CIRCe), University of Padua, Padua, Italy ABSTRACT During feld development of a microgrout for the stabilization of painted lime plasters detached from a limestone substrate, diethyl oxalate-based formulations out-performed microgrouts based on nanolime, colloidal silica and ammonium oxalate, creating more cohesive and homogenous set materials, with better working properties. However, unlike ammonium oxalate, diethyl oxalate is relatively new to the feld of conservation, and therefore requires extensive testing to understand its properties and the products of its reaction in calcium carbonate systems before it can be used in conservation treatments. The current study builds on previous testing, to compare the efect of variations in the formulation of diethyl oxalate-based microgrouts bulked with limestone powder, including the efect of application to dry and damp limestone substrates to understand its reaction mechanism, products and performance. ARTICLE HISTORY Received 5 December 2019 Accepted 6 May 2020 KEYWORDS Calcium carbonate; conservation; diethyl oxalate; microgrout; wall painting 1. Introduction Diethyl oxalate is a relatively new material to the feld of conservation but has recently been tested as a microgrout binder for the treatment of narrowly detached lime plasters (Porter et al. 2019). Like ammo- nium oxalate, diethyl oxalate reacts with calcium carbo- nate to form calcium oxalates (Conti et al. 2013, 2014a; Porter et al. 2019). However, prior to its testing as a microgrout binder, diethyl oxalate had only been eval- uated in laboratory studies as a conservation material for consolidation (Conti et al. 2013, 2014a). Many of its properties, reaction mechanisms and products therefore require further characterization before it can be consid- ered for use as a material for conservation treatments (Conti et al. 2013, 2014a; Porter et al. 2019). While previous work focused on the feld testing of a diethyl oxalate microgrout and its performance in com- parison with microgrouts prepared with more commonly used binders (including a nanolime preparation and ammonium oxalate) (Porter et al. 2019), the current study explores the properties of the diethyl oxalate itself and how the microgrout mixture can be modifed to optimize the performance of this binder, while also understanding how application conditions can afect its reaction. 2. Background 2.1. Microgrouts In wall painting conservation, narrow plaster delamina- tions (≤2 mm wide) are reattached to their support through the introduction of a bulked but fuid material, which can fow behind detached layers and reestablish adhesion between them and the substrate. While many of the design criteria and materials for stabilizing such detachments are identical to those of non-structural injection grouts designed for similar purposes, the restricted dimensions of the spaces to be flled require the use of a microgrout (Biçer-Şimşir et al. 2009). Like grouts for wall paintings, microgrouts have three main components (Pasian, Piqué, and Jornet 2017): ● Aggregate/s, which bulk the void and control shrink- age and cracking of the mixture upon drying and setting; ● Binder, which provides cohesion between aggregates and adhesion of the microgrout to surrounding material; ● Suspension medium, which provides fuidity to the mixture and normally also acts as the binder diluent. CONTACT Jennifer Herrick Porter jennifer.porter@um.edu.mt Department of Conservation and Built Heritage, University of Malta, Msida MSD 2080, Malta INTERNATIONAL JOURNAL OF ARCHITECTURAL HERITAGE https://doi.org/10.1080/15583058.2020.1773960 © 2020 Taylor & Francis