Introduction

The character of a wall is derived from many factors including the type of masonry used in its construction, its weathering characteristics, texture, colours and the care that has been taken in the construction process.

One of the most important, although often overlooked, elements in relation to this is the mortar pointing.

Pointing is the term given to the mortar finish that lies between the bricks or stones that have been used in the building process. The materials from which pointing is made and the manner in which it is applied can have a significant impact on the appearance of a building.

Pointing however is far more than just a visual feature and has a great bearing over the manner in which a building of traditional construction functions.

Buildings of traditional construction are those designed and built before the development of reliable and cost-effective impermeable membranes or moisture barriers. They rely instead on their ability to allow moisture to evaporate rapidly away, preventing a damaging build-up of damp and the resulting physical decay.

This category includes nearly all buildings constructed prior to 1919, as well as a significant proportion of those built before 1945. It is essential that works to these buildings should take into account the traditional technology and characteristic behaviour of the building fabric, otherwise severe damage can be caused.

Well-meaning attempts to keep moisture out of these buildings using modern methods tend to have the unfortunate effect of preventing vital

Conservation Advice Note No. 8

Pointing Good Practice Guidance

South Northamptonshire Council

evaporation and causes accelerated moisture-related damage to a building.

Traditionally constructed buildings were also built without the expansion and contraction joints of modern construction. They have however been built with flexible materials in such a way as to allow for safe and secure movement and settlement over time in a manner that does not cause harm to the building or its occupants.

Pointing is an important element in relation to these matters and serves both a visual and structural purpose. This conservation advice note seeks to help identify, explain and answer many of the common questions raised in relation to pointing and offers guidance to homeowners and members of the public on the most appropriate way in which the work should be undertaken.

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Pointing is an essential feature in many attractive brick and stone walls however when undertaken poorly using inappropriate materials and methods it can cause both visual and structural damage

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What is pointing?

Pointing is the term given to the ‘finish’ that is found between the bricks or stone used to build a house or any other masonry structure. It serves both a visual and structural purpose in buildings that are of a traditional construction.

Structurally pointing acts as a bedding between stones or bricks and provides some flexibility act-ing as a shock absorber between the masonry allowing for the movement and settlement of the structure over time. It also helps to spread the load evenly through the wall.

Pointing also works to prevent water penetration through the joints by its physical presence whilst at the same time allowing the wall to breathe and drain.

Walls need to breathe and if the pointing doesn’t allow this, the wall will rapidly deteriorate. Mortar joints are the lungs of a wall, they allow water within the structure to enter and leave freely. If water tries to leave through the stones or br icks they wi l l s lowly disintegrate. Block the mortar joints and the wall will destroy itself.

With this in mind pointing should always be subservient to the material the wall is built with and assume a secondary role.

As well as being a material, pointing is also the process of filling the outer parts of the joints in stone or brick walls where bedding mortar has been deliberately left out or raked back or where the surface has been weathered back from the face of the stone. The colour, texture and thickness of the pointing and the joints in which it is laid all have a significant impact on the appearance and character of the wall.

Repointing is the process of taking out and replacing the mortar from the face of a masonry joint. Done properly, it helps sustain the life and enhance the appearance of a structure. However, on an unfortunately large number of occasions it is poorly carried out using inappropriate materials and methods. This can result in harm being caused to both the appearance and structural integrity of the wall.

Pointing contributes to the character and appearance of many structures and can significantly alter their appearance.

Stone Pointing • Random Rubble Stone The irregular nature of this type of material often results in wide surface joints between the stones. Consideration needs to be given to this when pointing with a finish flush to the surface of the material often resulting in unacceptably wide mortar joints. As such the lime mortar should be slightly recessed from the face of the stone. • Coursed Rubble Stone Pointing Joints should be flush or slightly recessed. Pointing should not cover the edges of the stones or be spread over their faces.

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History of pointing

For over two thousand years the mortars used for pointing were considered only in relation to their structural properties applied as function dictated and finished flush with or slightly set back from the face of the masonry with appearance not given significant importance. It is only since the 18th century that the appearance of pointing has been refined for aesthetic and weathering purposes.

At that time the skill of the brick makers/masons improved and materials became more uniform in shape. This combined with the industrial revolution, which saw the mechanisation of the construction process and an enthusiasm for the practise of classical architecture had a significant impact on the way work was undertaken. The result was the development of a variety of pointing techniques which sought to enhance the appearance and significance of the masonry.

During the 19th century building technology also changed and cement was seen to replace traditional lime as the dominant mortar for use in works of pointing. From the Roman period until the 18th century mortars consisted of lime and gritty aggregate mixed together with sand. All ingredients were sourced locally and manufactured close to the construction site.

The introduction of cement affected the manner in which pointing was undertaken, changed the appearance of some buildings and resulted in the application of unsympathetic mortar finishes. A problem that is still encountered all too often today. Styles of finished pointing

South Northamptonshire has a variety of attractive brick and stone built properties. Wherever possible their historic pointing should be retained and its style copied in any repointing works that are proposed.

The most common and appropriate styles of pointing encountered in relation to these are as follows.

Examples of inappropriate (above) and appropriate (below) pointing to random rubble stone walls

• Beaked or double struck joints Beaked joints were used to improve the uniformity of the brickwork. This was achieved by pushing the tip of the trowel into the mortar to create a ‘V’ shape when viewed from the profile. • Weather Struck This is where the point is finished with its bottom edge level with the face of the brick and its upper set back creating a downwards slope which pushes the water away from the joint. • Curved indent brushed joint This is a brushed joint with a slightly concave finish that draws water to the face of the joint.

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• Ashlar Masonry Pointing Ashlar stonework is very finely jointed and requires a fine mortar without significant aggregate. The joints are often so narrow that repointing is unnecessary with attempts to repoint often resulting in damage to the masonry.

Brickwork Pointing • Tuck pointing This is sometimes seen and involves the creation of a mortar that is the same colour as the surrounding brickwork usually through adding brick dust to the mix and applying this flush with the brickwork. Prior to the mortar setting a groove is scored in it and a strip of white chalk ‘tucked’ into it. This finish is aesthetically pleasing as the mortar is not visible and only the straight white chalk can be seen creating the effect of fine gauged brickwork. • Penny rolled pointing This is where mortar is finished flush to the face of the brick and incised with a square edged object such as a penny or a trowel to form a groove 1-2mm thick running along the centre of the joint.

Extremely fine jointed pointing shows off the

Historical Penny Rolled (top) and Tuck Pointing

• Inappropriate weather struck and ribbon pointing.

These can cause both visual and structural damage to both brick and stone masonry and should not be used (see below)

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Weather struck pointing

Curved indent ‘brushed joint’

Flush joint

Reverse struck joint

Deep sunk joint

Raised ‘strap pointing’

Types of appropriate and inappropriate pointing finishes

Inappropriate ribbon pointing can harm the appearance of otherwise attractive buildings.

• Scheduling repointing work One of the keys to successful pointing is to plan the works well in advance. Pointing should not be carried out during periods of heavy rainfall, cold or extremely hot conditions and this needs to be considered when scheduling the works.

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Is repointing necessary?

The aim of repointing is to replace the weathered outer face of joints with new mortar. Decisions about the need for repointing must be carefully considered before any works are undertaken. When carried out properly repointing can help to prevent water penetration and the deterioration of the built fabric, it can also enhance appearance. However when undertaken poorly the results can be both visually and structurally damaging. Old mortars themselves are often of value as they present an irreplaceable record of past technology and building skills. As much of the old mortar as practical should always be retained. Complete repointing of an elevation is rarely needed or advisable nor is repointing that is undertaken purely as a cosmetic exercise to ‘tidy up’ the appearance of a building. Conditions indicating the need for repointing include: • Seriously decayed joints that are

weathered back to at least the equivalent of their width or are soft and crumbling.

• Severely eroded joints which give inadequate support to bricks and stone and encourage the ingress of water.

• Hard brittle joints exhibiting cracks or shrinkage especially where bricks or stones are decaying around them.

• Dense, impermeable joints trapping water and damaging the surrounding masonry.

Lime mortars can often appear soft but this in itself is not a sign of failure. Typical areas that may need repointing are the bases of walls, exposed wall tops, parapets, window arches, chimney stacks, cement pointing that is causing damage and areas around rainwater goods and pipes. Repointing good practice

If after careful consideration it is decided that repointing is necessary then the works should be undertaken with care by a suitably skilled person whilst having consideration to the following:

An exposed chimney showing signs of decay and the need for repointing.

The use of hard cement mortar can cause significant damage to the stone and bricks that it surrounds.

Trialling any new pointing that is needed on a small section of the wall is usually recommended especially where the works involve a listed building. Sample areas may need to be inspected and approved by the Local Planning Authority before any work commences. • Preparation Following the appropriate scheduling of the works proper preparation needs to take place. Any damaging vegetation that is present should be allowed to die back before it is carefully removed. Heavily saturated walls should also be allowed to dry out to an acceptable level. It is necessary to provide a sound base for the replacement mortar through the removal of decayed mortar from the face of the masonry. This is a process known as raking out and should be undertaken carefully using appropriate fine edged metal hand pointing tools. A depth at least equal to that of the width of the joint and usually not less than 40mm for rubble stone and 20mm for brickwork is recommended. The repointing of ashlar stonework is generally not desirable due to the quality of the original work and the risk of disfiguration that can occur. If repointing is necessary then care must be taken to avoid damage being caused and hand tools used to rake out the joints to a depth of approximately 10-12mm. The back of the raked out joint should be squared off allowing new mortars to be packed well into the corners. To ensure loose and decayed mortar is properly removed the area should be gently flushed through with water, taking care to clean the loose debris from the face of the stone. During the raking out process it is important to ensure that all vegetation and any penetrating roots are completely removed. This is necessary to stop future damage occurring should the roots re-grow. Once joints have been properly cleaned care needs to be taken to ensure that the mix of the replacement mortar is suitable and matches the surrounding mortar in terms of colour and

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In order for the works to be successful it is necessary to ensure appropriate access, mortar mixing areas, site protection, the correct equipment and that health and safety requirements are in place at all times. Where it is proposed to undertake pointing works on a listed building and its associated structures, the Local Planning Authority should always be contacted and advised of the scale of the works and the materials and methods that are to be used. If it is considered that the works will affect the special interest of a listed building then a formal application for Listed Building Consent will be required. This can take up to eight weeks to determine.

Sample areas showing the new pointing are recommended especially where works relate to a listed building.

impact on the new pointing. • Binder Lime is the most appropriate mortar for use in traditional structures. Lime mortars are flexible and can tolerate movement without failure. Traditionally constructed walls with flexible cores move and the properties of lime mortars complement this movement and prevent it from causing damage to the masonry. In modern wall construction the cavity which separates the inner and outer leaf ensures that any moisture that enters the structure is unable to travel to the interior face. In traditionally constructed walls the surface absorbs moisture but also releases it through its mortar joints allowing it to dry so that damp does not penetrate far into the building. This is only achieved as a result of the breathable qualities of lime mortars. Cements do not share these special characteristics and their use in structures of traditional construction should be avoided if harm is not to be caused.

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texture whilst also working with the breathable and flexible qualities of the building. Analysis of the existing mortar can be beneficial in this regard although a traditional lime based mortar should be used in all cases.

The Mortar Mix

All mortars contain a binder such as lime or cement (the sticky part which hardens in situ), and a filler (the majority of the mix) which is generally referred to as the aggregate. Depending upon individual circumstances an additional setting agent may also be added to the mix. When considering a new mortar mix the age and condition of the historic fabric of the structure should be as much of a consideration as the location of the masonry. The durability of the masonry is more important than the mortars which are intended to be sacrificial. Where the mortar specification is too strong the masonry itself will be put at risk; where it is too weak problems will also occur. Mortar mixes should always be created with this in mind and be softer than the surrounding stone or brick. The mix of new mortar should only be specified once the conditions and causes of eroded joints are fully understood and have been addressed otherwise they will continue to have an adverse

Vegetation can cause damage to the structures and needs to be carefully removed as part of the pointing process.

Cement mortars can cause visual and structural damage when applied to buildings of traditional construction.

eminently hydraulic giving the fastest and most durable set. These are referred to as NHL2, NHL3.5 and NHL5. For most general pointing, repair and building conservation work, moderately hydraulic lime is likely to be appropriate.

• Hydrated Lime (Non-Hydraulic Lime) Hydrated Lime (also known as ‘builders lime’) is the dry powder that you are likely to find in most DIY stores or builders’ merchants. It is a non-hydraulic lime although the manner in which it has been produced means that it is an inferior product to Lime Putty. This results from the length of time that it has been stored for and a certainty that an unknown proportion will have reacted with carbon dioxide by the time that it is needed for use. Whilst lime putty should be at least three months old before it is used and continues to improve with age, hydrated lime starts to deteriorate from the moment it is made. As such its use is not recommended in relation to buildings of traditional construction. Good quality, non-hydraulic lime putty is superior and should be used wherever possible. • Pozzolanic additives The term pozzolan derives from the volcanic ash found in the Pozzuoli area of Italy. It was originally used by the Romans to encourage the set of lime mortars and today it is used to describe several additives which can be added to non-hydraulic lime mixes to give them hydraulic properties. These include crushed brick, tile, pumice, ash and metakaolin. Unlike cement pozzolanic additives have properties which do not compromise the traditional flexible and permeable qualities of the lime mortars to which they are added. Although pozzolans are most often used in situations where rapid setting is required they are not necessary in all circumstances and it is generally the case that a simple non-hydraulic lime mortar will suffice.

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Lime types Lime for use in mortars is available in three main types: 1. Lime Putty (Non-Hydraulic Lime) 2. Hydraulic Lime 3. Hydrated Lime (Non–Hydraulic Lime).

• Lime Putty (Non-Hydraulic Lime) This is a high quality product compatible with the qualities of a traditionally constructed structure. Putty is usually sold wet in tubs and is matured. The longer it is matured the better with 6 months being standard for a good quality lime. Lime putties are easily worked and when cured they provide a good bond to masonry, are flexible and permeable. Mortars that are made with them do not however have a chemical set and dry slowly by reaction to air. This is a process known as carbonation and can take some time; as a result of this it is usually only recommended for use in sheltered locations. Lime putty mixes should not be gauged with ‘builders lime’ or cement in attempts to speed up their set as this can affect the qualities of the mix and cause harm to the building. Where there is a genuine need for a faster setting mortar special additives can be incorporated into the mix (see below).

• Naturally Hydraulic Lime (NHL) Hydraulic lime is produced from limestone containing clay and impurities such as silica and iron. Because of their composition hydraulic limes set in reaction to water to differing degrees of hardness. Mortars made with hydraulic lime have the advantage that they set more rapidly than lime putty but they are also harder and can be less permeable. Hydraulic lime is sold in bags and will always display NHL and a number on the label. This refers to the clay content and is an indicator of their strength and setting properties. There are three principal grades of hydraulic lime: feebly hydraulic, giving a weak set and relying mainly on carbonation; moderately hydraulic and

Using Lime Mortars

Once a suitable mortar mix has been chosen care needs to be taken over the manner in which it is mixed and applied. Although appropriate mixes will depend much upon the type of stone and the location of the works a recognised suitable general mix is 1:3 (lime to aggregate). Where the mix uses lime putty this is best made using a paddle mixer, by hand on a board or in a bucket, not a standard cement mixer. Hydraulic lime can be mixed in a standard drum mixer. Mixes should be made with care and not be too wet as this will affect the manner in which they can be worked and can cause shrinkage and cracking on drying. The type of binder that is used will also affect how and when the mortar can be made and care needs to be taken that mixes have time to develop before use but are not left so long as to become unusable. Re-pointing

Before repointing commences it should be ensured that all joints are dust free and well wetted. Lime mortars may not carbonate effectively at great depth and as such mortar should be applied in small amounts a section at a time to a depth of no greater than approximately 15mm. It is important that the mortar is well compacted in the joint and that no air pockets are present otherwise as it dries out the loss of moisture will cause the mortar to crumble. Mortar should be pushed firmly back into the joints using an appropriate pointing iron no wider than the width of the joint with the vertical joints taken first and then the horizontal. Works should start at the top of the wall and proceed downwards in an ordered sequence. When completed the joints should be filled with sufficient mortar so that it is roughly level with the face of the masonry ensuring that the width of the new joint is no greater than the original. It

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Aggregate The choice and quality of the aggregate has as much of an effect on the final mortar as the type of binder. Historically fillers have included sand and a wide variety of other materials such as earth, stone and brick dust, rubble and shell. Today the most common filler is sand. Sand is usually described as being either sharp or soft with much work today being undertaken with fine grained soft sand, often referred to as builders’ sand. This makes cement mortars easier to work but is not appropriate for use in lime mortar mixes. Well graded sharp sands should be used in traditional lime mortars as these provide good strength and will aid water permeability.

The type of aggregate affects the quality and finish of the mortar.

Traditional pointing enhances the significance and appearance of South Northamptonshire’s varied and attractive buildings.

sacks are often seen hung over walls to protect newly pointed masonry. Unless a specialised form of pointing exists, a lime based mortar and a flush or slightly recessed pointing style should be adopted for all works (see above). Such finishes are suitable for virtually all brickwork, this applies as much to Victorian, Edwardian and post war structures as it does to those from earlier periods, and all of the stone built properties and structures found within the South Northamptonshire District making a feature of the attractive local brick and stone.

is important to ‘finish’ the pointing so that it deflects water from the masonry rather than drawing it towards the face where it will cause damage. To prevent this, after an initial set, the pointing should be pushed back slightly and appropriately finished. This is a process known as ‘tamping down’ and is carried out with a stiff brush once the mortar has been given the opportunity to dry slightly. Undertaking this work will also ensure that the mortar is appropriately compacted. Finished joints should also be recessed to allow for the edges of the stones or bricks to be visible but not too much as to leave them vulnerable to frost damage. Carrying out this work also exposes the shapes and colours of the aggregate giving the joints a much more interesting finish and improves the contact between the edge of the stone and the mortar aiding performance and improving the weathering process. Care also needs to be taken to ensure that the mortar does not dry out too quickly or become damaged during the drying process. Remoistening by spraying after 24 hours and repairing any cracks that have appeared may be necessary. Protection of the joint and monitoring for a minimum seven day period is advisable. Damp sacking (Hessian is good) is a traditional response to this and

Sacking should be used to cover newly pointed walls to prevent damage being caused to the mortar by the weather.

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Summary

• Re-point only when necessary. • Take great care when removing defective

mortar, avoid using power tools and damaging the brick/stone.

• Use a lime based mortar. Cement rich mortars cause damage.

• Make sure that the mortar is subservient to the brick or stone. Ensure that mortar is weaker than the masonry that it bonds together and keep the mortar away from the outer surfaces of the stones.

• Avoid inauthentic/inappropriate joint finishes such as weather struck and ribbon pointing.

• Poor pointing can spoil the historic fabric both aesthetically and structurally and can lower the value of a property.

The Need For Consent

Some of the repointing work described above will require consent from the Local Planning Authority depending on the extent and nature of the work. Small scale works carried out on a strictly ‘like for like’ basis are unlikely to require consent but it is always advisable to check with the Local Planning Authority before proceeding with any works to a listed building. It should also be noted that works may also require Building Regulations approval before work can be commenced. Advice and Contact Details

For further advice on any issues identified in this Conservation Advice Note or any other building conservation matters please contact:

The Conservation and Heritage Team

South Northamptonshire Council Council Offices

Springfields Towcester NN12 6AE

Telephone: 01327 322265

Email: heritage@southnorthants.gov.uk

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Professional Advisors

English Heritage www.helm.org.uk

English Heritage publish specialist technical advisory leaflets. Society for the Preservation of Ancient Buildings (SPAB) www.spab.co.uk

SPAB offers guidance on historic buildings and many aspects of maintenance and repair. They publish technical pamphlets and hold various training days and courses. Institute of Historic Building Conservation (IHBC) www.ihbc.org.uk

The IHBC is a national body for professionals concerned with old buildings and their preservation, and it offers guidance on appropriate materials and methods of repair. Their website hosts a discussion forum on which people may post conservation related questions.

Useful Websites Building Conservation Directory www.buildingconservation.com Ancient Monuments Society www.ancientmonumentssociety.org.uk

Council for British Archaeology www.britarch.ac.uk

Victorian Society www.victorian-society.org.uk

Twentieth Century Society www.c20society.org.uk

Georgian Group www.georgiangroup.org.uk

Published August 2013

Please note that the information contained within this Guidance Note is correct at the time of publication. South Northamptonshire Council cannot be held liable for any changes that may have occurred since that time.