Understanding the science of historic buildings
What is a historic building?
Historic buildings are structures built years ago, ranging from few decades to many hundred years. They are typically constructed using naturally occurring or locally made rather than large-scale manufactured materials. Therefore they behave differently (for instance how they bear their own weight and that of the building's users: read our blog on this) compared to contemporary buildings which are built using industrial grade materials like steel, cement, and concrete.
In the short term using modern materials on a historic building may not seem problematic but over time their usage would substantially reduce the lifespan of a historic building. This is because the composition and properties of both are completely different.
For example, historic buildings would have walls of stone, brick, or even mud and not concrete or breeze blocks. They would have lime as both mortar (material binding wall components) and plaster (finishing material for walls) instead of cement. Their roofs would be timber or clay tiles rather than concrete. Floors would be lime concrete, oxide, tiles, or stone not vitrified tiles.
How are historic materials different from modern ones?
These materials allow structures to breathe, they are elastic (can resume their shape when stretched or compressed) and permeable (absorb and release moisture through ongoing carbon cycle on lime, oxide flooring, tiles, timber: read our blog on this) whereas modern materials are designed to do the opposite, they are meant to be plastic (cannot resume their shape when stretched or compressed) and impermeable (completely lock out all moisture). This is true right from foundation to walls, roof, and paint finishes (for instance water based paints are historic while acrylic based ones are modern).
Load or stress, therefore, work differently on both, making it a rather futile exercise to provide any guarantees as per modern materials and construction technology standards, whether in terms of number of years, factor of safety (FoS) or similar modern gauges of measurement. Additionally, the stone, lime, brick, or timber used on a historic building would be local - from the same region (given difficulty in transporting materials over long distances). For instance, the composition of a brick and lime structure in Mysore would not be the same as that in Bijapur; Begur limestone's properties are not the same as Karwar limestone's. Unless modern construction standards are not only re-calibrated for historic materials but also for non-uniformity in material composition of lime as mortar, for example, applying them on historic buildings would be pointless.
Why do they need special attention?
Problems usually arise because people undertake repairs by blindly applying modern materials and technology on historic buildings without considering their essential differences. Often it is the incompatible repairs that cause the problems and not the historic materials in themselves. Additionally, historic materials would be compatible to micro-climate related building or structural stress, as they are local, which a standard modern material may or may not be able to withstand (as they are standardized they are typically designed to withstand average temperature ranges).
High cost in production given their limited local area of usage, time and skill required to work with them unlike modern materials and other factors, including, modern being seen as developed and historic materials being seen as primitive, have resulted in such materials and construction technologies no longer being used widely.
This makes it essential to work with trained professionals, namely conservation (or preservation / restoration) architects, who will examine and suggest solutions to maintain, repair, and usefully extend their lives. Provided works are carried out as per best practices, as specified, and employing skilled labour who know how to work with historic materials, such buildings will stand for many generations to come.
For example, historic buildings would have walls of stone, brick, or even mud and not concrete or breeze blocks. They would have lime as both mortar (material binding wall components) and plaster (finishing material for walls) instead of cement. Their roofs would be timber or clay tiles rather than concrete. Floors would be lime concrete, oxide, tiles, or stone not vitrified tiles.
How are historic materials different from modern ones?
These materials allow structures to breathe, they are elastic (can resume their shape when stretched or compressed) and permeable (absorb and release moisture through ongoing carbon cycle on lime, oxide flooring, tiles, timber: read our blog on this) whereas modern materials are designed to do the opposite, they are meant to be plastic (cannot resume their shape when stretched or compressed) and impermeable (completely lock out all moisture). This is true right from foundation to walls, roof, and paint finishes (for instance water based paints are historic while acrylic based ones are modern).
Load or stress, therefore, work differently on both, making it a rather futile exercise to provide any guarantees as per modern materials and construction technology standards, whether in terms of number of years, factor of safety (FoS) or similar modern gauges of measurement. Additionally, the stone, lime, brick, or timber used on a historic building would be local - from the same region (given difficulty in transporting materials over long distances). For instance, the composition of a brick and lime structure in Mysore would not be the same as that in Bijapur; Begur limestone's properties are not the same as Karwar limestone's. Unless modern construction standards are not only re-calibrated for historic materials but also for non-uniformity in material composition of lime as mortar, for example, applying them on historic buildings would be pointless.
Why do they need special attention?
Problems usually arise because people undertake repairs by blindly applying modern materials and technology on historic buildings without considering their essential differences. Often it is the incompatible repairs that cause the problems and not the historic materials in themselves. Additionally, historic materials would be compatible to micro-climate related building or structural stress, as they are local, which a standard modern material may or may not be able to withstand (as they are standardized they are typically designed to withstand average temperature ranges).
High cost in production given their limited local area of usage, time and skill required to work with them unlike modern materials and other factors, including, modern being seen as developed and historic materials being seen as primitive, have resulted in such materials and construction technologies no longer being used widely.
This makes it essential to work with trained professionals, namely conservation (or preservation / restoration) architects, who will examine and suggest solutions to maintain, repair, and usefully extend their lives. Provided works are carried out as per best practices, as specified, and employing skilled labour who know how to work with historic materials, such buildings will stand for many generations to come.
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