Monuments and Monument Decoration Lab
Belgium abounds in valuable immovable heritage: monuments, archaeological sites, listed buildings, etc., often beautifully decorated with ornaments, sculptures, murals or mosaics. We provide analyses and research that contribute to better knowledge of our stone heritage and support its sustainable management or restoration.
Preliminary study for restoration
Structural engineers, geologists, chemists, conservators-restorers, industrial engineers, and laboratory technicians: we are a wonderful mix of profiles and the most prominent team within the Royal Institute for Cultural Heritage. Together, we are fully dedicated to the care of our architectural heritage.
"Most of our time is spent on lab analyses and on-site research, as part of preliminary studies for the restoration of listed buildings", says Laurent Fontaine, head of the lab. "We usually take samples on location. Then, in the lab, we identify the composition and physical properties of the materials used (natural stone, brick, mortar) and any finishing layers. Our research takes into account the specific characteristics of each building. This allows us to propose the most appropriate solution for their conservation and restoration.
At which stage of the restoration should you contact us?
We prefer to be involved from the very beginning, during the preliminary study. We offer careful analysis and interpretation of the study results, including recommendations for treatments or interventions. This is why we intervene less frequently when a project has already started.
You can also call on our expertise in the context of archaeological research. We can analyse the composition of wall paintings and mortars or determine the origin of natural stone. This research is carried out in close cooperation with the other laboratories and conservation studios of the Royal Institute for Cultural Heritage, such as the Stone Sculpture Studio, the Decoration of Monuments Unit, the Wall Painting Studio and the Radiocarbon Dating Lab and Dendrochronology Lab.
Our research takes the specific characteristics of each building into consideration in order to propose the most appropriate solution for their conservation and restoration.
Study of historical mortars
The study of the composition of historical mortars adds to our knowledge of building history and helps us search for compatible repair mortars. Mortar is the 'glue' between natural stones or bricks and is used for plastering masonry. Mortar mainly consists of a binder, usually lime or cement, and an aggregate: grains of sand whose size and mineralogy vary greatly. We identify the ingredients and proportions based on a sample of just 5 cm³ (± 50 g). We use three complementary techniques to do this:
- For the petrographic examination, we study a thin section of the mortar under a polarisation microscope using transparency to provide information about the properties of the aggregate, the type of binder, the presence of inclusions or any additives, etc.
- In a TGA-DSC or simultaneous thermal analysis, which combines thermogravimetry (TGA) with differential scanning calorimetry (DSC), the mortar sample is slowly heated up to about 1200°C. The measured physical reactions are then compared with the temperature of the mortar sample. From the measured physical reactions and phase changes of the mortar, we can deduce to what extent the mortar mixture is hydraulic. This tells us whether it hardens when it comes into contact with water or air.
- Finally, the amount of insoluble residue allows us to determine the binder-aggregate ratio quantitatively. For this purpose, the mortar sample is immersed in a hydrochloric acid solution, then filtered and calcined.
Identification of natural stone
Our experts usually identify the stone with a magnifying glass at x10 magnification based on macroscopic characteristics. In other cases, a petrographic examination of a thin section gives a definitive answer. The latter requires a representative sample of at least one cm³.
To determine the exact origin of the natural stone, the Institute can conduct additional investigations. We generally delve into the professional literature or call upon our extensive professional network.
Finishes and murals
Dr Marina Van Bos: "We study painted finishing layers and murals in both interiors and exteriors, on wood, stone, plaster or metal." Thanks to the identification of the different layers and the pigments, binders or metal applications used, we gain more insight into:
- the original colours and pigments, sometimes hidden under several paint layers
- previous restoration interventions and sometimes their dating
- degradation phenomena
- compatibility between ‘old’ finishing layers and new paint layers to be applied
Moisture and salt research
Vincent Crevals and Julie Desarnaud: "Both moisture and salts can affect natural stone and bricks. They can form salt efflorescences and visible moisture stains but also cause damage to stone materials, such as granular disintegration and fragmentation, which can result in significant material losses. The conservation-restoration of old buildings, sculptures and archaeological sites must therefore always consider these two factors."
To map the moisture or salt load, we can use various techniques, such as gravimetry, ion chromatography, X-ray diffraction and modelling of the salt behaviour in different climatic conditions. The result is a scientifically-based diagnosis of the current state of the monument or object. Based on this, we propose interventions to improve future preservation conditions.
We also carry out salt remediation tests. Sebastiaan Godts: "We try to bring the salt concentrations down to an acceptable level. If that is impossible, we propose an alternative approach, such as setting up a climate where the salts are kept as stable as possible to prevent the problem from spreading."
Moisture transport and modelling
Determining moisture and salt contents can also be carried out as part of a comprehensive study of moisture migration in façade masonry. We look at how the façade materials absorb water and dry out again when it rains and then evaluate the risks of damage caused by frost or rain penetration. This risk assessment is based on:
- A study of the physical material characteristics of the façade materials and any previous treatments. This is done through an on-site survey of water absorption employing Karsten tube measurements and analyses in the lab to determine the absorption levels, drying and pore structure (mercury porosimetry).
- The modelling of moisture flows through the façade masonry based on actual climate conditions. For this purpose, we use the Delphin software of TU Dresden.
This research gives us an insight into the damage mechanisms and allows us to evaluate potential conservation and restoration treatments to provide appropriate advice for a sustainable intervention.
Consolidation treatment and other stabilising interventions
A stone consolidation treatment is sometimes required to stabilise or prevent damage to monument façades and sculptures. However, not every treatment is suitable for every situation, and the wrong choice can worsen the damage in the long run. We can help you by:
- determining whether a stone strengthening treatment is necessary and, if so, how it should be carried out
- advising you on the appropriate treatments and products, such as repair mortars, fixatives, protective layers (such as a hydrophobic treatment) or finishing layers.
Tanaquil Berto explains how the team works to determine the need for a consolidation treatment: "Using a DRMS survey, we measure the hardness profile of the brick or natural stone to determine the depth and degree of weathering. We drill a hole with a diameter of 4.8 mm perpendicular to the stone surface. If the test reveals substantial granular disintegration, we proceed with a test consolidation treatment. We then repeat the DRMS measurements to evaluate the effect. This results in concrete advice for the site or project manager."
Climate study and monitoring
The lab also carries out climate studies to support the management of moisture and salt problems. Studies to evaluate and optimise the indoor climate in collection management are carried out in close cooperation with the Preventive Conservation Unit. We also advise on the possibilities and risks of energy renovation of historical buildings.