How to Mix and Use Mortar for Repointing 

19th Aug 2024 -

Repointing mortar joints is an important skill for maintaining and restoring buildings. This article delves into the techniques of mixing and using mortar specifically for repointing applications. We explore the optimal mortar mix ratio of ingredients, achieving the right consistency and methods for applying mortar.

• How to Mix Mortar for Repointing: Pro Tips for Perfect Application
• How to Repoint Brickwork: 8 Advanced Techniques
• What is the Best Mortar Mix for Repointing?
• Can You Repoint Over Old Mortar?
• How to Remove Mortar for Repointing
• How Much Mortar Do You Need for Repointing?
• Buy Excellent Ready Mix Mortar at Competitive Trade Prices

How to Mix Mortar for Repointing: Pro Tips for Perfect Application

To boost mortar performance, advanced techniques improve the quality and durability of your work. Here, we delve into these methods for mixing mortar. 

Precision mixing techniques

Accurate measurement of components is crucial for the consistent quality of mortar mixes. Use calibrated containers or scales for precise ratios. Consider using a moisture meter to assess sand dampness, adjusting water content accordingly.

For larger jobs, automated mortar mixers with digital controls ensure batch-to-batch consistency.

Hot and cold weather mixing

In hot weather, use chilled water and store sand in shaded areas to prevent rapid setting. Add a set-retarding admixture for extended working time. For cold weather, warm the water and sand before mixing. Avoid using frozen materials and consider a set-accelerating admixture to promote proper curing in low temperatures.

Customised aggregates

For historic projects, use custom-blending aggregates to match the original mortar texture and colour. This might involve combining different sand grades or incorporating crushed stone dust. Experiment with various aggregate combinations to achieve the desired aesthetic and performance characteristics.

Colour matching techniques

Analyse the existing mortar colour and create multiple small batches with slight variations in pigment ratios. Apply samples to the wall and allow them to dry completely before making a final selection. Remember that mortar typically lightens as it cures.

Mixing for optimal workability

Achieve ideal plasticity by mixing mortar in 2 stages. First, combine dry ingredients thoroughly then add water gradually while mixing continuously. Allow the mortar to rest for 15-20 minutes before final mixing. This period improves workability and helps prevent shrinkage cracks.

Read our comprehensive mortar mixing article for more information. 

How to Repoint Brickwork: 8 Advanced Techniques

While basic techniques serve well, advanced methods can transform a repointing project. The following techniques offer solutions for challenging scenarios and methods to achieve superior results.

1. Deep joint filling

For joints deeper than 25mm, use a 2-step filling process. Apply the first layer to about half the joint depth. Allow it to reach thumb-print hardness and then apply the second layer. Known as "packing," it ensures better compaction and reduces the risk of shrinkage cracks.

2. Pressure injection for narrow joints

With extremely narrow joints or areas with limited access, consider using a pressure injection system. This involves injecting specially formulated mortar under controlled pressure, ensuring complete filling of voids and excellent adhesion.

3. Tuckpointing for appearance

In cases where a uniform joint appearance is desired, use the tuckpointing technique. Apply a base layer of mortar matching the brick colour. After, insert a thin line of contrasting mortar to create the illusion of fine joints. It requires precision and practice but greatly improves the appearance of brickwork.

4. Ribbon pointing for historic preservation

For some historic buildings, ribbon pointing may be appropriate. This involves slightly recessing the bulk of mortar and applying a thin ribbon of finer mortar along the joint edges. It creates a distinctive shadow line and can help protect the edges of soft bricks.

5. Tooling for weather resistance

Advanced joint tooling can improve weather resistance. Use a slicker or weather joint tool to compress the mortar surface, creating a dense, water-shedding profile. For maximum durability, tool the joint when the mortar is at optimal hardness. 

6. Staged repointing for large areas

When repointing large wall sections, use a staged approach. Work in manageable areas, typically 5-10 sq ft at a time. This ensures proper attention to each joint and allows for consistent tooling before the mortar sets too much.

7. Curing control

Proper curing is key for mortar strength and durability. Use burlap sheets soaked in water to cover freshly pointed areas, maintaining moisture for several days. In hot or windy conditions, consider using curing compounds that allow for proper hydration while protecting against rapid drying.

8. Quality control measures

Regularly check joint depths, mortar consistency and tooling profiles. Use a pH meter to monitor the curing process, especially for lime-rich mortars. Document weather conditions, mix ratios and curing procedures for each section of the job.

What is the Best Mortar Mix for Repointing?

The best mortar depends on various factors and there is no one-size-fits-all solution. Below, we outline the mortar types to help you make informed decisions. 

Portland cement-lime mortar

• Type N: General-purpose mortar suitable for most repointing jobs.
• Type O: Lower strength, high lime content and ideal for soft masonry.
• Type S: Higher strength and suitable for load-bearing walls or areas with high moisture exposure.
• Type M: Should be used cautiously for repointing. Its high strength may damage softer bricks and restrict necessary movement in masonry. 

Lime mortar mix

• Non-hydraulic: This lime mortar mix for repointing sets by carbonation, is very flexible and ideal for historic buildings.
• Hydraulic: Sets by reaction with water, stronger than non-hydraulic lime and good for moderately exposed areas.

Custom blended mortar

• Specially formulated to match specific requirements in terms of strength, colour and properties.

Mortar mix ratios for different applications

Soft masonry (e.g. historic bricks, soft stone)

A mix ratio of 1 part Portland cement to 2-3 parts lime to 8-9 parts sand is often appropriate. The lime-rich mix provides the softness and flexibility needed for these materials.

Medium hardness

Medium hardness masonry might use a mix of 1 part Portland cement, 1-2 parts lime to 6-7 parts sand. This provides a balance of strength and flexibility suitable for various applications.

Hard masonry

Hard masonry can handle a stronger mix, typically 1 part Portland cement, 1 part lime to 5-6 parts sand. The higher cement content provides the strength needed for harder materials.

Pure lime mortar

For some historic applications, lime mortar repointing mix is used in a ratio of 1 part lime to 3 parts sand. 

Explore our guide on mortar mix ratios to learn more about boosting project quality.

Can You Repoint Over Old Mortar?

It is recommended that repointing should not be done over existing mortar. Proper repointing requires the removal of deteriorated mortar to a sufficient depth before applying new mortar. This ensures a strong bond and addresses underlying issues. Below are 6 reasons against repointing over the old mortar. 

• Adhesion issues: New mortar may not properly adhere to the old mortar surface, leading to failure and potential water infiltration.
• Trapped moisture: Applying new mortar over old may trap moisture within the wall, leading to deterioration of both mortar and masonry units.
• Underlying problems: Repointing over old mortar may conceal deeper issues such as cracks, voids or severely deteriorated mortar deeper in the joint.
• Aesthetic concerns: The resulting joint profile may be irregular and visually unappealing. 
• Structural integrity: The new layer may not contribute to the structural stability of the masonry. 
• Difficulty in future repairs: Multiple layers can complicate future mortar repair and repointing efforts.

How to Remove Mortar for Repointing

As detailed above, proper removal of deteriorated mortar is important for repointing. This process, known as raking out, requires careful attention to detail and the right techniques to avoid causing damage. Below is a comprehensive guide to mortar removal. 

Assessment

Start by inspecting the joints to determine the extent of mortar deterioration. Identify the type of masonry and original mortar composition. This will help your approach to removal and replacement. Mark the areas that need repointing, typically focusing on sections where the mortar is visibly crumbling or cracked. 

Repointing tools

Gather a range of tools for the job. Hand tools such as hammers, chisels, jointing tools and wire brushes are key for precise work. For larger projects, power tools like grinders with diamond blades or reciprocating saws with masonry blades speed up the process. 

Depth of removal

As a general rule, remove mortar to a depth of 2 to 2.5 times the width of the joint. For most brick joints, this means removing to a depth of about 12.5-25mm. Make sure that the removal depth is uniform across all joints for a stable base for the new mortar.

Manual removal technique

Start the removal using a hammer and chisel, working carefully from the centre of the joint outward. Use a jointing tool to scrape out any loose mortar that remains after chiselling. Be careful to avoid damaging the edges of the bricks or widening the joint beyond its original dimensions.

Power tool technique

When using a grinder with a diamond blade, make 2 parallel cuts in the centre of the joint. You should then chip out the middle section. Like with manual removal, take care when working near the edges of the masonry units to avoid causing any damage.

Cleaning the joint

After the bulk of the mortar has been removed, use a wire brush to clean out any remaining debris from the joint. For a deeper clean, use compressed air to blow out dust and loose particles, ensuring a clean surface for the new mortar. 

Dealing with stubborn mortar

For extremely hard mortar that resists standard removal, consider using a masonry chisel and club hammer for more focused force. In particularly challenging cases, it may be necessary to use a small rotary drill to create pilot holes before chiselling. However, this should be done with great care.

Handling different masonry types

Adjust your technique based on the type of masonry. For soft brick or stone, use extra caution and rely more on hand tools to prevent damage. Engineering brick may require more aggressive use of power tools because of its hardness. 

Preparing for repointing

Once the old mortar has been removed, clean and dampen the joint. This prevents rapid drying of the new mortar when it is applied. Take this opportunity to check for any hidden damage that may have been exposed during the mortar removal process.

How Much Mortar Do You Need for Repointing?

The quantity of mortar needed varies significantly based on several factors. Here is a detailed breakdown to help you calculate mortar requirements.

Calculation process

• Measure the wall area: Measure the length and height of the wall area to be repointed in sq ft or square metres. For complex walls with openings, measure each section separately and sum the total. Total Wall Area = Length × Height.
• Calculate joint length: Estimate the total length of joints to be repointed. This can be done by the following.
  a) Counting the number of courses (horizontal) and joints (vertical) in a sample area.
  b) Multiplying by the wall dimensions. For example, in a 1 square metre sample with 10 horizontal and 20 vertical joints: Total horizontal length = 10 × wall width; Total vertical length = 20 × wall height. Total joint length = horizontal length + vertical length. 
• Determine joint size: Measure the width and depth of the joints to be filled. Standard joint widths are typically 10mm for brickwork but may vary.
• Calculate volume of mortar: Volume = joint length × joint width × repointing depth
• Apply wastage factor: Add 10-20% for wastage during mixing and application. 
• Convert to practical units: Convert the volume to bags of mortar mix or components (sand, lime, cement) as needed.

Key considerations

• Mortar shrinkage: Account for slight shrinkage during curing by adding 2-5% to the calculated volume.
• Joint profile: Concave or weather-struck joints may require slightly more mortar than flush joints.
• Historic mortars: When matching historic mortars, factor in additional material for colour matching and testing.
• Large projects: For extensive repointing jobs, consider calculating quantities for manageable sections to make sure you always use fresh mortar. 
• Material density: Be aware that the density of mortar components may vary. 
• Contingency planning: Consider adding an extra 5-10% as a contingency to avoid material shortages.