Question 1

1. What is hydrated lime?

Accepted Answer

Hydrated lime, also known as calcium hydroxide, is a fine, dry powder produced by carefully adding water to quicklime (calcium oxide) during manufacturing. This chemical process results in a stable, easy-to-handle product that is widely used in construction, agriculture, and industry. Hydrated lime can also be supplied as a pliable paste called lime putty, which is ideal for mixing with sand to create lime mortar for historic buildings, pointing, and rendering. Its high purity, natural reactivity, and excellent workability make it a preferred choice for stabilising soils, improving soil quality, and producing eco-friendly mortars that support breathability and moisture regulation in old and new structures. Its long-standing use in traditional masonry and modern eco-construction underscores its versatility and importance in sustainable building practices.

Question 2

2. What’s hydrated lime used for?

Accepted Answer

Hydrated lime is a versatile additive commonly used in construction to enhance the properties of various materials. In mortar, it improves workability, flexibility, and water resistance, making it easier to apply and helping the finished wall resist cracking and moisture ingress. It is also widely incorporated into plaster and render mixes to increase adhesion, strength, and durability, especially when working on heritage buildings or exterior facades exposed to the elements.

Additionally, hydrated lime can be used to stabilise soils, improve ground support, and produce eco-friendly, breathable plasters that regulate moisture and prevent damp issues. Its natural high alkalinity and compatibility with traditional building materials make it an essential component for restoring, repairing, and maintaining structural integrity across a wide range of construction projects.

Question 3

3. What’s the difference between hydraulic and hydrated lime?

Accepted Answer

Hydraulic lime and hydrated lime are distinct products, each suitable for specific construction applications. Hydraulic lime is designed to set and harden through a chemical reaction with water, even in damp or wet conditions. It is particularly suited for restoration and repair work on historic buildings, as it allows for building movement and maintains the breathability of the masonry, helping to prevent moisture build-up and damage over time. Hydrated lime, on the other hand, is a pre-prepared powder produced by adding water to quicklime. It’s widely used to improve the workability, water resistance, and durability of mortar, plaster, and render in both new build and refurbishment projects. Hydrated lime offers a more predictable setting time and is ideal for use in stabilising soils, internal building finishes, and traditional lime mortars where breathability is less critical. Both products play vital roles in ensuring building longevity, structural integrity, and heritage preservation when used appropriately.

Question 4

4. How should I mix lime mortar?

Accepted Answer

To achieve optimal results, mix lime with sand in ratios suitable for your specific application—generally around 1:3 for pointing or internal finishes, and 1:2 for structural use. Begin by thoroughly combining the dry ingredients to ensure an even distribution of lime and sand. Gradually add clean water, mixing steadily until you reach a smooth, workable, and creamy consistency. The mixture should be pliable enough to spread easily without being too wet or runny, which could weaken the bond. Always follow manufacturer’s guidelines or project specifications for best results. Properly mixed lime mortar enhances adhesion, flexibility, and longevity—crucial for both restoring historic structures and supporting modern builds.

Lime

Blue Circle Hydralime Hydrated Lime 25kg

Hanson Hydrated Lime 25kg

Rugby Hydrated Lime 25kg