Building and Pointing with Lime Mortar

A Course Overview

This practical, hands-on training day introduces the principles and techniques for selecting, preparing, applying, and curing lime mortars to repair and conserve traditional masonry and brickwork. The course is intended for builders, contractors, conservation professionals, property owners, maintenance teams, and anyone involved in repairing historic brick or stone buildings. 

The training combines classroom discussion, demonstrations and supervised practical work. It focuses on using lime mortars in a way compatible with traditional masonry, allowing walls to remain vapour-permeable and accommodating the movement and moisture behaviour of older buildings.

The emphasis is on understanding that no single “standard” lime mortar exists. The correct mortar depends on the building's age, materials, exposure, condition, and construction.

Main aims

By the end of the day, participants should be able to:

- Explain the differences between air lime, hydraulic lime and cement mortar.

- Identify the principal components of a lime mortar.

- Select an appropriate binder, aggregate and mortar strength for a particular application.

- Assess the condition and requirements of existing masonry.

- Prepare joints correctly before repointing.

- Accurately measure and mix lime mortar.

- Apply, compact and finish mortar using appropriate tools.

- Understand the importance of damp curing and protection.

- Recognise common defects caused by poor materials, workmanship or curing.

- Work safely when handling lime and carrying out masonry repairs.

 Programme

Participants arrive, sign in and receive an outline of the day. The trainer confirms the practical arrangements, personal protective equipment requirements and any relevant health and safety information.

The day begins with an overview of lime mortars and traditional construction. Participants consider how older masonry walls manage moisture, movement and vapour transmission.

 Topics include:

 - Solid brick and stone wall construction.

- Historic mortars and their changing composition.

- The relationship between masonry units and mortar.

- Why traditional walls often require softer and more permeable mortars.

- The potential damage caused by dense, hard or impermeable cement-rich repairs.

 The principle is introduced that mortar should generally be sacrificial: it should be able to weather and be repaired without causing unnecessary damage to the surrounding masonry.

 Lime binders and mortar materials

The trainer, Dr Mark Womersley, explains the main types of lime used in conservation work.

Air lime

Air lime sets primarily by reacting with carbon dioxide in the atmosphere. It may be supplied as lime putty or hydrated powder. It is generally suitable for many sheltered or moderately exposed traditional applications, provided that adequate protection and curing are provided. This lime may be prepared as a hot-lime mix, which will be discussed and demonstrated.

Natural hydraulic lime

Natural hydraulic lime, or NHL, contains naturally occurring reactive compounds that allow it to set partly through hydration and subsequently carbonate. Different strengths, such as NHL 2, NHL 3.5 and NHL 5, are intended for different conditions. The strongest product is not automatically the most appropriate.

Hydraulicity and testing

Participants are shown why the term “hydraulic lime” should not be assumed solely from the source stone or historic description. A lime's behaviour depends on its composition, manufacture, storage, and mixing. Where the specification is uncertain, testing and compatibility assessment may be necessary.

Aggregates

Aggregates make up the bulk of the mortar and strongly influence its performance. The session covers:

- Sharp and well-graded sands.

- Local sands and colour matching.

- Grain size and texture.

- The effects of excessive fines.

- The use of brick dust, stone dust or other additions where historically appropriate.

- Avoiding overly uniform or excessively fine mixes.

Participants examine examples of sands and completed mortars to compare colour, texture and workability.

Assessing existing masonry and choosing a mortar

This session explains how to select mortar for the building rather than choosing it based solely on nominal strength.

Participants learn to consider:

- The age and construction of the wall.

- The type and condition of the brick or stone.

- Exposure to wind, rain and frost.

- Existing mortar composition and strength.

- Salt contamination and damp conditions.

- Whether the work is repointing, bedding, rendering, harling or patch repair.

- The visual and historic requirements of the building.

The trainer demonstrates basic methods of inspecting joints, including identifying loose, friable, cement-rich or overly hard mortar. The group discusses when further investigation, sampling or laboratory analysis may be appropriate.

The group explains general mixing principles, including typical volumetric ratios such as 1:2.5 or 1:3 binder to aggregate for particular hydraulic lime applications. It is stressed that ratios are indicative only and must be adjusted according to the binder, aggregate, application and site conditions.

Preparing masonry for repointing

Before the practical work begins, the trainer demonstrates how to prepare joints correctly.

This includes:

1. Carefully removing loose or failed mortar.

2. Avoiding unnecessary damage to brick arrises or stone faces.

3. Raking joints to an appropriate depth.

4. Cleaning out dust and debris.

5. Pre-wetting the masonry.

6. Allowing excess surface water to drain before filling.

7. Protecting adjacent surfaces and architectural details.

This demonstrates the difference between sound preparation and merely applying mortar over a defective surface.

Lunch is provided

Participants take part in a supervised mixing exercise.

The demonstration covers:

 - Safe handling of lime products.

- Accurate measurement by volume.

- Dry blending of binder and aggregate.

- Gradual addition of water.

- Mixing time and consistency.

- Recognising a workable but cohesive mortar.

- Avoiding over-wet mixes.

- Adjusting the mix where the aggregate or site conditions require it.

- Cleaning equipment and preventing contamination.

The trainer explains the differences between hand mixing and mechanical mixing, including the need to avoid overworking certain lime materials.

The finished mortar should be workable enough to compact fully into the joint, but not so wet that it slumps, shrinks excessively or washes out during curing.

Practical building and repointing exercise

Participants practise building and repointing on a historic building in Halifax, or on a suitable training wall.

The practical exercise includes:

- Filling the back of the joint rather than merely coating its surface.

- Working in manageable lifts where joints are deep.

- Compacting the mortar firmly.

- Avoiding voids and pockets.

- Keeping mortar off the face of the masonry.

- Forming an appropriate joint profile.

- Finishing at the correct stage of set.

- Brushing away surface laitance and loose crumbs.

- Matching the texture and appearance of adjacent work.

Different finishes may be demonstrated, including flush, slightly recessed, weather-struck or suitably traditional textured finishes. The choice of finish relates to the building's historic character and exposure, rather than personal preference alone.

Curing, protection and common defects

Correct curing is essential to lime mortar performance. The trainer explains how to protect fresh work from:

- Direct sunlight.

- Strong wind.

- Heavy rain.

- Frost.

- Rapid drying.

- Excessive heat.

- Physical disturbance.

Depending on the mortar and weather, freshly applied work may require careful damp-curing for several days. Coverings should allow ventilation while reducing rapid moisture loss. Adapt the duration and method of protection to the material, season, and exposure.

Common defects are reviewed, including:

- Cracking and shrinkage.

- Powdering or friability.

- Poor adhesion.

- Colour variation.

- Failed arrises.

- Surface washing.

- Salt staining.

- Hard cement-rich repairs.

- Inadequate joint preparation.

- Over-wetting or under-wetting the substrate.

- Insufficient curing.

Participants learn how to distinguish defects caused by the material, the application technique, and site conditions.

Review, assessment and questions

The day concludes with a review of the main principles. Participants discuss the practical exercise, compare the sample panels and identify the factors that influenced the final appearance and performance of the mortar.

Learning outcome

At the end of the training day, participants will have a practical understanding of how to approach lime mortar work responsibly. They will be able to prepare a masonry joint, mix an appropriate mortar, apply and finish it correctly, and protect it while it cures.

The course does not replace site-specific design, conservation advice or specialist structural assessment. It provides a sound foundation for carrying out small-scale lime mortar repairs and for making informed decisions about more extensive work on historic buildings.

All on site at our training location at a 17th-century property in Northorwam Halifax, West Yorkshire.