Prompt Mortar

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A specialist mortar which combines the benefits of lime with the rapid set of Roman Cement. Suitable for building and pointing stone and brick in demanding situations.

Prompt mortar is one of our ‘conservation mortars' used in the repair of historic buildings. As its name suggests, Prompt mortar sets rapidly, which makes it the perfect solution for those situations and climatic conditions where normal hydraulic lime mortar would take too long to go off. This, combined with its low strength, ease of use and long-life performance makes it a first choice for conservation work and restoration projects.

This fast set mortar is available in a range of colours and can be supplied in 25kg sacks for ease of handling, or in bulk bags for use if extra speed and convenience is needed.


Prompt Mortaris a dry pre-bagged lime mortar made with natural hydraulic lime and Prompt Roman cement


  • Walls breathe (vapour permeability)
  • Low shrinkage (reduction of cracks)
  • Excellent adhesion
  • Maintains the mortar's low modulus of elasticity
  • Fast set allowing work to continue in adverse condition
  • Warm natural colour - light ochre
  • Excellent sulphate resistance

Packing and availability

Available in 25 kg paper bags 


Repointing: 20kg/m² stonework; 7kg/m² brickwork.

Per 1000kg: will lay 900-1200bricks.

Rendering:1 bag will cover 1.25-1.4m2 at 10mm thickness

All figures approx.


To a 25 kg sackadd only 3.5 to 5 litres of clean water. Mix for 3 to 10 min.


Before pointing or building clean and remove all dust and loose material from joints and masonry, and adequately dampen dry or high suction surfaces. Pointing and building mortars should be finished the same day. Prompt / Lime mortars also require curing.


Prompt mortars do set rapidly, however always protect the mortar against the effects of drying winds, strong sunlight, rain and frost. In warm weather gently mist spray with water after application and cover if required with damp hessian sheets. In cool weather cover fresh mortar with protective


 Image showing The Ribblehead Viaduct, North Yorkshire - Lime Green's Prompt Mortar offers a highly effective conservation solution.

Repair mortar for the Ribblehead Viaduct


Spanning quarter of a mile and standing 100 feet above the valley it crosses, the Ribblehead Viaduct has long been an iconic landmark on the historic Settle-Carlisle Railway Line. But its location on the barren moorland of North Yorkshire means that this Grade II Scheduled Ancient Monument is constantly exposed to high winds, heavy rain and low temperatures.

The Requirement

An ongoing programme of repointing is required to keep the viaduct in good condition. Given the conditions, any mortars used in repair and preventative maintenance work have to be of the highest specification to ensure the viaduct's 1.5 million bricks and limestone blocks, weighing as much as 8 tonnes, remain structurally sound.

The Problem

  • Specified mortars must be able to withstand the expansion and contraction that comes from frequent temperature changes and to allow the old 140-year old bricks and blockwork to breathe. So they must be robust enough to deal with high moisture levels and able to flex without cracking.
  • Mortars must also meet the strict requirements of the organisations responsible for maintaining ancient monuments, and be in keeping with the original materials used.
  • From a practical perspective, the mortar has to remain sufficiently workable so it can be applied even in bad weather conditions.

The Solution

Under such conditions, Lime Green's Prompt Mortar offers a highly effective conservation solution. Used for repointing where conditions are challenging, such as on exposed castle walls, bridges and canals, or where works have to be completed within a tight time schedule, as in the case of tidal stonework.

As its names suggests, Prompt Mortar is specifically designed to go off fast by incorporating a traditional binder - also called prompt. This was used before the development of Portland Cement, and when mixed 'neat' will set in just three minutes!

The Benefits

  • By mixing prompt with our lime mortars, we can introduce rapidity of set in a traditional lime mortar base. This makes it the perfect solution where normal hydraulic lime mortar would take too long to go off.
  • The introduction of prompt binder has no discernible impact on the breathability of lime.
  • Prompt Mortar is easy to handle, as 25kg bags can be mixed on site.
  • It can also be applied when working temperatures are little more than freezing, which means longer working periods even in winter.
  • Prompt Mortar also has the structural strength to cope with bad conditions, providing a robust pointing solution.
  • It comes in a range of colours and can be matched to existing mortars, so maintaining visual continuity.
  • Prompt Mortar has been carefully designed to minimise the cracking that can occur when water within the mortar tries to escape to the surface.

Lime Green's Prompt Mortar may have a long history, but we've made sure that it remains very much a modern-day solution where speed of set is essential.