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Lime Structural Consolidation

Roman Lime as Structural Consolidation Material
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Structural Consolidation and Repair

Nowadays the structural consolidation of older walls and buildings is often done with cement-based mortars or concrete, for a number of reasons:

  • Low cost: being produced in large quantities, cement mortars are economical, making them a favorite in budget-oriented projects.
  • Mechanical strength: cement provides the necessary mechanical strength to withstand significant loads, which can be advantageous in various construction scenarios, particularly where robust structural support is required.
  • Wide-spread use in the building industry: the prevalent application of cement in the building industry, especially in modern constructions and new-build applications, underscores its continued popularity.
  • Lack of awareness of the damages cement can cause to old structures: despite the popularity of cement, many are unaware of its potential to cause harm to older structures. Its usage without acknowledging these risks can lead to irreversible damages.
  • Unawareness of building-friendly alternatives: the dominance of cement as the go-to construction material overshadows other, more compatible options for historical buildings.

However, there is more to structural consolidation than just cement. Cement's advantages, such as cost-effectiveness and mechanical resilience, often come at the expense of the long-term health of heritage buildings, adding to their deterioration over time. This is where the importance of alternative materials comes into play, particularly those that are sympathetic to the original construction methodologies.

The Romans have developed lime-based alternatives, building some impressive structures that have lasted for centuries using lime mortars. The Colosseum or the Pantheon in Rome are just some examples of Roman architecture fully built with lime about 2,000 years ago that still stand today. These ancient edifices signify the remarkable durability and compatibility of lime with historical building techniques, highlighting its advantages in maintaining and restoring older buildings. lifespan of these treasured buildings, ensuring that their historical and architectural significance is preserved for future generations.

Colosseum — A Lime Structural Consolidation Masterpiece

One prime example of lime being used as a structural material is the Roman Colosseum, which was built between 70 AD and 80 AD on the site of an artificial lake Nero had constructed. The building was oval-shaped measuring 189 meters by 156 meters, which is almost twice as long and 1.5 times as wide as a modern football field. It has been built from an estimated 100,000 cubic meters of travertine stone (a local limestone) plus bricks and tuff blocks held together by lime-based Roman cement.

Due to the poor condition of the soil beneath the amphitheatre, a deep and strong foundation was required. The foundation, with more than 12m thickness, was constructed by two layers. The ground has been dug out until it reached the clayey bottom of the lake, creating a 31m wide elliptical crown. The bottom of this colossal trench has been filled with 6m of lime-based roman cement - a mix of lime mortar, volcanic pozzolans and pieces of basaltic rock - forming the first layer of the Colosseum's foundation. The second layer consisted of multiple layers of well beaten, compacted stones, gravel and Roman mortar. Drainage has also been put in place to take away the streams that flow from the surrounding valleys and hills.

structural reinforcement of old walls
The Colloseum in Rome, built around 80 AD. It has been standing for 2,000 years on a 6 metre thick lime foundation

The reliance on lime-based structural materials doesn't just end with the Colosseum. The historical utilization of lime in construction exemplifies why it's an ideal choice for preserving the integrity of older structures. Lime mortar not only provides excellent breathability but also accommodates the natural movement of historic buildings, avoiding the harmful effects like cracking and moisture accumulation that cement may cause over time. This adaptability makes lime an invaluable component in conservation efforts, illustrating a timeless approach that aligns with the original architectural intent.

Lime Structural Consolidation and Crack Repair

Today, the Betoncino Consolidante MGN Roman mortar serves as an exceptional lime-based structural consolidation and reinforcement mortar, ideal for a wide range of consolidation and repair projects. It is also suitable for use as a bedding or building mortar in diverse construction projects.

This highly resilient mortar offers remarkable resistance to salt and water, ensuring robust performance even in harsh environments while delivering enduring, sympathetic repairs. As part of a certified lime structural consolidation system, it caters effectively to the needs of any old or listed building. The accompanying video illustrates the concept.

Explore the application of Roman structural lime to consolidate and strengthen building elements. The example below demonstrates how effectively it can reinforce an old door frame, highlighting its value in conservation projects.

Recommended Products

Here are the typical recommended materials / products for this solution. Other product variations are possible as we have different types of plasters and paints, depending on your needs or application. Please get in touch to discuss additional options.

Work Specifications

Here are the recommended work specifications for this solution.

betoncino-main-core-conservation

Base, Consolidation, Flooring, Building

Betoncino Consolidante MGN

[20-40 mm] Structural Consolidation lime plaster, in 20 – 40 mm or more thickness, applied as:

  • â–ˆ [10 – 15 mm] Consolidation plaster, coat 1
  • â–’ [Mesh] Structural reinforcement mesh (20 x 20 mm, 40 x 40 mm): embedded between coats for additional reinforcement and flexibility.
  • â–ˆ [10 – 15 mm] Consolidation plaster, coat 2. Etc.
modena-featured-core-conservation

Pointing, Consolidation, Building

Modena M5 MGN

[20-40 mm] Structural Consolidation lime plaster, in 20 – 40 mm or more thickness, applied as:

  • â–ˆ [10 – 15 mm] Consolidation plaster, coat 1
  • â–’ [Mesh] Structural reinforcement mesh (20 x 20 mm, 40 x 40 mm): embedded between coats for additional reinforcement and flexibility.
  • â–ˆ [10 – 15 mm] Consolidation plaster, coat 2. Etc.

Plaster Application

Here are some key application points about the application of each plaster, as well as links to the full application guides. Please have your plasterer read / watch the application instructions before applying the product. If any questions, please contact us, happy to help.

betoncino-main-core-conservation

Base, Consolidation, Flooring, Building

Betoncino

  • Clean the masonry: the plaster must be applied on a cleaned and uniformly wet substrate. All crumbling and loose parts must be removed by brushing so the masonry is free of dust, salts and oils. If possible, also wash the walls with a pressure washer; this will clean and wet the walls in one go. Close larger holes with lime mortar and pieces of bricks.
  • Salt-inhibitors or PVA bonding agents are NOT needed and should not be used before the application of this plaster. This natural lime plaster bonds very well on its own.
  • Mixing: mix the material with clean tap water only without adding anything else (no other material or additive), until a homogenous, creamy-consistency mix is obtained. 
  • IMPORTANT: Dry to wet mixing: plasters with hydraulic ingredients should always be mixed from dry to wet (workable) state. Add your powder to a bit of water, start mixing and gradually add more water till the right consistency is reached. This is the right way. Mixing the other way – wet to dry mixing – by starting with lots of water then gradually adding powder to the right consistency, is incorrect. Reason: excessive wetting weakens the plaster, alters its hydraulic set resulting in less performant, more friable and shorter lasting plasters.
  • Application: apply the plaster in 10 mm coats.
  • Light key: give the plaster a light key using a wet brush. Do not cut into the material with the edge of a trowel.
  • Additional coats can be applied in further 10 mm increments. Use an embedded fibreglass mesh for extra reinforcement over the recommended thickness.
  • Drying time: the plaster dries quite quickly, typically in 1-2 days, depending on ambient conditions. Once it has hardened, the next coat can be applied.
  • Application conditions: ambient and wall temperatures must be between +5 to +30°C during application. Surfaces should be protected from rain and humidity until they have completely dried (approx. 3 – 10 days depending on weather conditions).
modena-featured-core-conservation

Pointing, Consolidation, Building

Modena M5

  • Clean the masonry: the plaster must be applied on a cleaned and uniformly wet substrate. All crumbling and loose parts must be removed by brushing so the masonry is free of dust, salts and oils. If possible, also wash the walls with a pressure washer; this will clean and wet the walls in one go. Close larger holes with lime mortar and pieces of bricks.
  • Mixing: mix the material with clean tap water only without adding anything else (no other material or additive), until a homogenous, creamy-consistency mix is obtained. 
  • IMPORTANT: Dry to wet mixing: plasters with hydraulic ingredients should always be mixed from dry to wet (workable) state. Add your powder to a bit of water, start mixing and gradually add more water till the right consistency is reached. This is the right way. Mixing the other way – wet to dry mixing – by starting with lots of water then gradually adding powder to the right consistency, is incorrect. Reason: excessive wetting weakens the plaster, alters its hydraulic set resulting in less performant, more friable and shorter lasting plasters.
  • Application: apply the plaster in 10 mm coats.
  • Additional coats can be applied in further 10 mm increments. Use an embedded fibreglass mesh for extra reinforcement over the recommended thickness.
  • Drying time: the plaster dries quite quickly, typically in 1-2 days, depending on ambient conditions. Once it has hardened, the next coat can be applied.

Completed Projects

Here are some of our projects using this solution:

Photo Galleries

Here are some photos demonstrating this solution. Click on any image to open the photo gallery.

Videos

Here are some videos related to this solution. Please unmute the videos when playing them.

Any Questions? Need Technical Advice?

If you have any questions about a project, a problem, a solution, or any of our plasters - please get in touch.

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