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Roundtower Lime
The Forge,
Innishannon,
Co. Cork,
Ireland.
T12 W72X
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Lime is an integral building material that has been used for centuries due to its versatility, durability and sustainability. When considering using lime for your construction or restoration projects it is important to understand the fundamental differences between hydraulic and non-hydraulic lime. These varieties of lime each have exclusive applications and properties. This article will explore the characteristics of these two types of lime to help guide you to make an informed decision for your building projects.
Hydraulic lime is a form of lime that can set and harden once exposed to water. This material contains reactive silica and alumina which contribute to the hydraulic properties. This lime type is available in different grades, categorised as NHL (Natural Hydraulic Lime) with differing degrees of hydraulicity.
This type of lime is also known as air or fat lime. Non-hydraulic lime does not set or harden when exposed to water. It is composed of pure, high-calcium limestone with minimal impurities. This lime type cures slowly through a carbonation process, this is when carbon dioxide is absorbed from the air causing the lime to harden.
Setting Time - The biggest difference is that hydraulic lime has a much shorter setting and hardening time when exposed to water, whereas non-hydraulic lime cures more slowly through a natural carbonation process. Therefore, hydraulic lime is more appropriate for projects that require a much quicker setting time, such as when damp conditions are present.
Hydraulicity - Non-hydraulic lime is unreactive to water. Hydraulic lime has a variety of degrees of hydraulicity, these determine its setting properties. NHL 5 is very hydraulic and sets quickly whereas NHL 2 has the lowest hydraulicity and sets more slowly.
Strength - Hydraulic lime is typically stronger than non-hydraulic. Therefore, this lime type is suitable for load-bearing applications and places that are put under high stress.
Flexibility - Non-hydraulic lime is more flexible which allows for more movement in buildings than hydraulic lime. This lime type can adapt to the natural contraction and expansion of materials without shattering.
Breathability - Non-hydraulic lime allows moisture vapour to permeate through so it is often considered more breathable. This feature can help stop moisture-related issues within buildings.
Masonry: Hydraulic lime is typically used for repointing and repairing historic masonry structures, where its quick setting time is necessary.
Plaster: It can be used appropriately in plastering applications, particularly in damp environments.
Pavements and Mortar: Hydraulic lime is suitable for constructing mortar and pavements due to its durability.
Historic Restoration: Non-hydraulic lime is used commonly for restoring historic buildings where authenticity and breathability are fundamental.
Sustainable Building: Non-hydraulic lime has low energy consumption and carbon-negative properties, so aligns with sustainable building practices.
Lime Wash: This lime type is great for creating traditional lime washes as it provides a breathable and natural finish to surfaces.
When deciding between hydraulic and non-hydraulic lime it is important to understand the specific requirements of your building project. Hydraulic lime is suitable for various applications, particularly when moisture control is an issue as it offers rapid setting and strength. Alternatively, non-hydraulic lime is authentic, flexible and sustainable, making it popular for historic restorations and eco-friendly buildings. Understanding the properties and suitable applications of these lime types is essential to achieve your desired construction project.