Repeated crystallisation of salts in the pores of building materials is a common cause of damage in buildings. Sodium chloride (NaCl) is one of the most common salts, responsible for weathering in the built environment. Mortars, especially when used as plasters and renders on the surface of walls, experience fast degradation as they are exposed to conditions perfectly conducive to salt weathering. As a consequence, their service life is often compromised, requiring frequent replacements. Costs associated with replacement interventions have a high economic and a social impact. Over the last two decades, the use of crystallisation inhibitors as an additive to prevent/mitigate salt crystallisation damage in building materials has shown promising results. Sodium ferrocyanide (NaFeCN), a crystallisation inhibitor of NaCl is particularly effective in preventing damage by inhibiting/delaying NaCl nucleation and altering NaCl’s crystal habit. When mixed-in air lime-based mortars, NaFeCN has been shown to considerably improve the salt weathering resistance....@en

Bioreceptivity is a natural phenomenon that has been observed on building material for many years. Bioreceptivity is when materials are being colonized by one or more species of living organisms without necessarily going under biodeterioration. (Guillitte, 1995) Based on the literature, bioreceptivity depends on three main factors: on climatic conditions, the topology of the colonized element and the material.
By considering these variables, this research focuses on engineering a workflow capable of supporting bioreceptivity-oriented design. More specifically, it investigates how computational performance analysis and optimization can support the integration of bioreceptive materials in customizable building elements, which could be produced by digital fabrication.
For research purposes, the research is split in two main parts which run in parallel. This research takes as a case study mosses, which generally cannot withstand high solar radiation and are dependent on water for their survival and reproduction.
The first part, investigates on a digital model, how surface topology modifications could improve bioreceptivity by reducing the solar radiation of a surface while directing water over them. This is approached by a script which examines through a case study, to what extent the solar radiation of a surface topology could be reduced through topological modifications and which factors influence it. Even if the average solar radiation of the case study was significantly reduced through an optimization process, it is not clear to what degree topology can contribute to the improvement of bioreceptivity because this fact can only be validated physically.
The second part, focuses on lime-based mortars and examines how their composition can affect bioreceptivity. Based on the literature, material properties like high water capacity, high water retention, permeability and high total porosity can benefit bioreceptivity. Four different lime-based mortars were tested, through laboratory experiments, seeking the relation between their water transport behavior and bioreceptivity. Grain size distribution in combination with binder to aggregate ratio are the main factors which influence mortars’ transport behavior. In order to observe the relation between their water transport behavior and bioreceptivity, a moss growth experiment was conducted in a controlled environment. The short timeframe of the experiment makes it difficult to draw definitive conclusions.
The methodology that was developed in these two parts, is finally attempted to be combined in a bioreceptivity-oriented design approach in order to express a new architectural vocabulary. Through a research-by-design approach, three design approaches are conceptualized, compared and prototyped, raising the potential of bioreceptive applications.

The preservation and restoration of intricate stucco ornaments, which are part of our collect cultural Heritage, is under threat due to a diminishing number of skilled restoration plasterers. The highly physically demanding- and labour intensive nature of this work makes it unsustainable for the human body and advocates for a more sustainable alternative restoration method for the future. Digital Fabrication has the potential to offer such an alternative method. While 3D scanning, digital repair and 3D printing are all proven technologies, stucco ornament restoration often requires an on site fabrication solution directly onto a ceiling or wall due to the brittle nature of prefab stucco elements. The research explores how an in-situ 3D printing technique can be developed for the restoration of stucco ornaments by focussing on three main topics: 1) developing gypsum-based 3D printing materials, which are compatible to gypsum ceilings and comply with criteria for extrusion based 3D printing; 2) Designing and prototyping 3D printing tools including an extruder and material delivery system; 3) Conceptualizing a Restoration Robot Platform with which the developed printing material can be used with the developed 3D printing tools, for on site stucco ornament restoration. The insights gained from the development of the printing material and printing process are integrated into digital fabrication software used in practise, through a proposed plug-in and workflow.

Damage due to the crystallization of salts is a common problem in porous building materials. Also mortars used in the restoration of historic buildings are often subjected to a high salt load, resulting in a rapid degradation and high maintenance costs. Especially lime-based mortars, used for example as render, plaster, bedding mortar or pointing mortar, are vulnerable to this type of damage. Despite the extensive research efforts, no definitive solution yet exists to tackle the problem of salt decay in building materials. Existing solutions to improve mortar resistance with respect to salt decay such as modifying the moisture transport properties of the mortar (e.g. plaster with water-repellent properties) or increasing its mechanical strength of the plaster mortar (e.g. by using a different binder such as cement), often show compatibility problems and might cause even more damage to the to be restored (historic) fabric. Recently a new approach, based on the use of crystallization modifiers to alter the salt crystallization process, has been proposed. The aim of modifiers is to prevent or mitigate salt crystallization damage in building materials. Modifiers are ions or molecules that can keep the salts longer in solution (inhibitors), facilitate the precipitation of a certain crystal phase (promoters) and/or change the shape and size of the grown crystals (habit modifiers). These effects are often present in combination, i.e. a promoter or inhibitor can at the same time act as habit modifier. @en