Which Lime?

 

We have outlined the basic information below. The type of lime required, its constituent parts and the amount of its application are often unique to a building. Care should be taken to understand if any existing materials can be conserved and to what degree old mortar needs to be removed.

Lime (for traditional building purposes) is generally available in three forms:

  1. Lime putty in the form of a soft cheese commonly available in tubs. This is a pure lime and is normally white or creamy in colour.
  2. Hydraulic lime as a powder in three different grades. It contains impurities or pozzolans such as calcites and silicates that are useful when a stronger mortar is required for damper or more exposed areas such as cellars or chimneys.
  3. Ready mixed mortars using both types of lime.

Under no circumstances should Hydrated lime be considered for any form of mortar. This is commonly available from builder’s merchants.

  1. Lime putty should be used with caution. It very caustic and should generally be used by only the most experienced professional. As ready mixed mortars are commonly available these should be used unless a specific mix of sands is required to create a particular colour or quality.
  2. Hydraulic Lime is commonly available in three types and should be mixed with differing quantities of sand.
    1. NHL 2 – Feebly hydraulic similar to a lime putty. Mix 3 parts sharp sand to 1 part lime
    2. NHL 3.5 – Moderately hydraulic. Mix 2.5 sharp sand to 1 part lime
    3. NHL 5 – Strongly hydraulic. Mix 2 parts sharp sand to 1 part lime.
  3. Ready mixed wet mortars are commonly available in 25kg or 1 ton bags but have a short ‘shelf life’. Dry hydraulic mixed mortars are also available.