East Herts District Council - Brick Repointing and Repair

Some early examples date from the mid-fifteenth Century and the Tudor, Elizabeth and Jacobean periods - such as Rye House, Stanstead Abbotts (c1443), Hertford Castle Gate House (1461-5), part of Hunsdon House (1525-8), the hunting lodge at Queen Hoo, Tewin (early Elizabethan), The Lordship, Standon (1546) and Hadham Hall (c1575). These earlier bricks tend to be principally in the red-orange range of colour. There are also many fine later C17 and Georgian buildings in all of the towns and some villages. Regency, Victorian and Edwardian brickwork can also be of high quality and interest and the brickwork of modest Victorian terraces and smaller houses and other buildings contributes greatly to the character of the District's conservation areas.

These later bricks covered a wide range of colours from traditional dark reds, reds and oranges to browns, yellows, purples, blues, greys, creams and whites. By the nineteenth Century large quantities of bricks were imported into east Hertfordshire and so began the decline in the previously extensive traditional localised brick manufacture based on small scale kiln production using local clays. There are now no brick works in East Hertfordshire.

Most listed buildings in East Hertfordshire incorporate some brickwork in their structure. In timber-framed buildings the frame is generally on a brick base and the chimney stack, whether original or inserted in an already existing house (in the late C16 or early C17 as a 'modernisation'), would be of brick construction. Even medieval churches may have a later brick porch or some additions in brick. In conserving and repairing old brick walls or chimney stacks, a thorough understanding of the brick - its origins, texture, size, colouring and weathering properties - and the techniques and craft of construction, such as the bond and especially the composition of the mortar and the finished joint or pointing profile - is essential.

The earlier bricks were relatively thin - typically about 2" in width though sometimes thinner and sometimes wider. These red-orange bricks were employed only in buildings of high status and it was not until the later sixteenth Century that they were in more general use - and only then in superior buildings for the most part. By the C17 brick became more widely used due to fashion and a marked decline in oak and other structural timber for building. Brick manufacture was also associated with tile production, which was replacing thatch at this time. There was an attempt to regulate brick size in 1625 and during the seventeenth Century there was a move from the general use of English bond to Flemish bond.

Brickwork reached new heights of sophistication and excellence from the 1660's and during the C18 with precisely detailed window and door arches using soft rubbed and gauged bricks and meticulously accurate tuck pointing. The Brick Tax of 1784 slowed demand for brick building and stucco became popular principally in the towns.

New industrial techniques throughout the nineteenth Century allowed for mass production of standardised bricks of consistent colour. In 1840, the Imperial brick of a nominal size of 9" x 4¹/₂" x 3" was widely adopted. Yellow 'London stock' bricks and yellow/grey Gault and cream and white bricks became increasingly popular. Portland cement was used in mortars in the latter part of the nineteenth Century with a resulting change in the character of brickwork. Red brick continued to be widely used however, especially in the neo vernacular and Arts and Crafts inspired houses of the late Victorian and Edwardian periods.

Is listed building consent needed?

Listed building consent will be required if the repair or repointing proposed is not a matching like-for-like repair using the same mortar composition, finished pointing profile and matching brick and bond. It should be remembered that it is a criminal offence to alter a listed building without first obtaining listed building consent.

The penalties can be heavy. A fine historic brick wall or chimney stack can be ruined by ill informed or thoughtless, bodging so called repairs. Once carried out, such works are often difficult or impossible to reverse and reinstate without extensive damage to the brickwork.

If you are in any doubt please contact the Conservation Officers in the Planning Department, before you commence repairs or repointing. It may be necessary to provide a specification of the works or a sample area of repair or repointing to be agreed before work can begin.

Conservation and repair of historic brickwork

Terrible damage to once beautiful walls and chimney stacks has occurred by ill advised or simply crude attempts at repair, that severely diminish the historic character and value of the building in itself and often that part of a conservation area. It is possible to achieve a close match to old bricks using carefully selected new hand made bricks or second hand bricks, but exact replacement is impossible - the source of the original clay, methods of manufacture, weathering characteristics, ageing and 'pleasing decay' cannot be reproduced. Great care should be taken to salvage and reuse existing bricks where possible.

Cutting out damaged or spalled bricks should be undertaken with great caution to prevent damage to surrounding sound bricks. By using a fine, sharp chisel surrounding joints may be cut out and raked back before removing the failed brick. Replacement bricks must 'match' in every respect - size, strength, colour, texture and , if possible, degree of weathering. Inserted bricks can stand out like bright 'sore thumbs' and have a most disconcerting effect in a mellow old wall. Close attention to maintaining bond, using lime based mortar and matching pointing profile is essential.

Mortar ('plastic') repair to spalled brickwork should be avoided. It is almost always unsightly and unsatisfactory and should only be considered in exceptional circumstances and in small areas of individual bricks. Brick dust is best used to colour the mortar. Artificial colouring agents are likely to fade.

The cause of large bulges, large cracks or fractures must be carefully investigated and a decision made to leave alone, cut out and point, stitch and grout in situ or to take down and rebuild. If the wall is stable and there is no obvious structural failure or water penetration the best solution is often to leave well alone. If there are large obvious or unsightly cracks, that may allow excessive water penetration into the wall, it is often advisable for these cracks to be stopped with lime putty mixed with brick dust to achieve matching colour.

Intervention should be the minimum necessary to retain the wall or chimney stack in a safe and sound condition.

Brick Bond

The bonding of historic brick walls is an important part of its interest providing a characteristic pattern, texture and richness. Most old brickwork is bonded in English bond (alternative courses of headers and stretchers). From the late C17 and especially since the C18 onwards most brickwork is built in Flemish bond (headers and stretchers alternatively in the same course). Occasionally early brickwork may be found in a random bond with no discernible pattern.

Some other lesser used historic bonding types are: English garden wall bond, rat trap (or Chinese) bond, Flemish garden wall (or Sussex) bond and header bond. It is essential that repairs, alterations or extensions to historic buildings should faithfully match the existing bond.

Repointing Historic Brickwork using Lime Based Mortars

Repointing old brickwork requires considerable skill and expertise. Incorrect diagnosis and the use of inappropriate methods of repair and unsuitable mortars are amongst the most common causes of damage to the character, appearance and structural soundness of historic brick walls. A great deal of unnecessary repointing of brickwork is carried out.

Morttar joints serve two main purposes: To bed bricks neatly so as to take up any differences in size or shape; and to effectively fill and weatherproof the joint between bricks whilst allowing the free evaporation of moisture. Sound old pointing should be retained as this is an important element in the character of historic walls. Repointing work shall only be undertaken where absolutely necessary and by agreement with the conservation officer of the District Council.

If existing joints or pointing need to be forced in raking out it is unlikely that repointing is necessary. Repointing is generally only needed when mortar has clearly failed and is powdery, loose and crumbling or has weathered or eroded away or decayed.

Obvious causes of localised failure, such as blocked, overflowing gutters or damaged rainwater downpipes should be repaired before repointing and brick repair takes place.

Repointing of brick walls and chimney stacks to listed buildings and other historic brickworks should be carried out using lime based mortar, which is compatible with the strength, porosity and texture of the brick and a close match to the original mortar.

As a general principle, the mortar should be slightly weaker than the brick to allow the wall to 'breathe' and for moisture to evaporate through the joints and to discourage excessive moisture loss through the face of the brick - which would accelerate the rate of decay. The inclusion of cement in a mix should be restricted to the minimum absolutely necessary and, if possible, it should be avoided altogether. The finish to the new pointing should carefully match the existing original profile.

Preparation for Repointing

The existing weathered and friable or otherwise failed joints or pointing shall be carefully raked out by hand to a depth of between 25mm and 40mm - or at least to twice the width of the joint.

The open joint should be thoroughly brushed cleaned of dust and flushed out with clean water (avoiding saturation).

Suitable tools for cutting out joints are fine, sharp chisels, flat bladed quirks or plugging chisels. Hacksaw blades can be useful for fine joints.

The use of mechanical cutting discs/angle grinders is not acceptable as this is likely to cause great damage to arises and increase the width of joints or to cut into the bricks. Sand blasting or the use of other grit or abrasive cleaning is unacceptable.

Mortar Mix for Repointing

Lime putty based mortars should only be used. As a rough guide, a mix such as 1 part lime putty: 3 parts sand - well washed and well graded with a large proportion of coarse sharp sand is generally suitable for old brickwork in a relatively sheltered position with a fairly coarse texture.

At warm, dry times of the year, when frost is unlikely (between mid-April and mid-November) the addition of cement is generally not necessary. Repointing should not be attempted if there is a threat of frosty weather conditions. When a small amount of cement is required, white cement is usually preferred, as the colour of the lime-based mortar can then be determined solely by the sand. The usual proportions are 1 part binding agent (lime putty or lime and a small addition of cement, or lime and a pozzalanic agent - such as finely ground brick dust) to 3 parts sand - part sharp sand (well washed and well graded). In the past mortar was almost always simply a mix of local sands and lime - to give a porous and flexible material ideally suited to this use. The mortar should be prepared with the minimum amount of water required to give a cohesive and workable mix. This will reduce the overall amount of shrinkage which inevitably takes place when using a lime-based mortar.

Cement-based mortars are unacceptable for historic old brickwork. Repointing in a strong cement and sand mortar is a disaster for an old wall. It will prevent the wall from breathing and lead to the rapid degradation of the brick - especially the soft red stock bricks characteristic of old walls in East Hertfordshire. By preventing the evaporation of moisture through the mortar joint, following rainfall or other wetting, the trapped moisture can only evaporate through the external face of the brick. Through frost action and/or the crystallisation of soluble salts, the exposed face of bricks will begin to deteriorate, then break down or flake, leading to widespread spalling and disintegration of the brick wall with typical concave "powder weathering" of the brick once the surface has gone, with the hard joints or pointing standing out. Cement based mortar joints also look harsh and hard.

Slightly weathered mortar is very rarely the cause of dampness and water penetration through a wall. Repointing old brick walls should bot be seen as a means of 'toughening up' or 'waterproofing' a wall - this is a misguided idea that has resulted in hard cement based mortars being used for repointing and has caused great harm.

Repointing Technique and Pointing Profile

Once carefully raked out, the joint should be cleaned of dust and residual mortar particles by brushing and then thoroughly flushed out with clean water (avoiding saturation). As the repointing is carried out, if the joints have dried, they must be rewetted before placing the new mortar so as to control suction, especially in warm or drying conditions.

A pointing iron or a wood spatula should be used (not a steel trowel) to push the mortar into the joint as firmly as possible. Repointing should faithfully replicate the existing original pointing profile - where this can be ascertained. In most old brickwork the mortar face will be finished as a neat flush joint (depending on the original profile and treatment) or very slightly recessed where, for example, the arises of the bricks are damaged or rounded through weathering, so that the mortar does not spread across the face of the brick, giving an over prominent wide appearance to the joint. Perpendicular joints are filled before bed joints.

Other special forms of pointing or jointing should be carefully matched, such as 'tuck' pointing or 'lined' pointing, dating from the C18 or C19. Gauged or rubbed brick arches in Georgian or Edwardian brickwork should only be repointed in exceptional circumstances and then only be an experienced specialist craftsmen, as the fineness of the joint makes this a highly skilled and time consuming operation. If rebedded, only fine lime putty should be used for the joints. Comparatively recent forms of joint finish or pointing such as 'weather-struck', 'bucket handle' or raised 'strap' or 'ribbon' pointing are quite unacceptable in historic brickwork.

In terms of the appearance of the old brick wall it is important to match the texture of the surviving weathered flush pointing by using the same proportion of coarse sharp well graded sand and roughening the surface of the mortar joint, as it sets and hardens, by lightly stippling and tamping the surface with a brush or rubbing with sacking, a stick or a wooden spatula to raise the grit present in the mortar. The finish should not have a brushed or dragged appearance but should be finely tamped with the brush to give and even roughened finish. This roughening should be carried out as work proceeds to give a consistent appearance. Great care should be taken to avoid smearing mortar onto the faces of the cricks and thorough cleaning should take place as work proceeds.

In periods of adverse weather conditions for repointing, i.e. cold or hot or rapids drying weather, if it is not possible to postpone work until more favourable conditions, the repointed brickwork should be completely protected by sacking or tarpaulins (and periodically lightly dampened if there is concern for excessively rapid drying), for up to 7 days or longer as necessary.

If the new areas of repointing are obviously standing out in the old wall, in some circumstances it may be desirable to tone down the surface by the application of a soot wash (prepared by immersing a cloth bag of soot in a bucket of water for about 24 hours). Repeated applications should be carried out until the desired tone is achieved. Other artificial colorants should be avoided.

In many situations a sample are of the proposed repointing will be required to be provided for inspection by the conservation officer. Once agreed, this can be used as a reference area for other repointing. The areas to be repointed shall be specifically agreed and defined. Repointing is to be restricted to the minimum necessary and it should not be assumed that whole walls may be repointed if only a part has failed.

Do's and Dont's

Do Use the lime putty based mortar for repointing and rebedding bricks.

Do Restrict repair and repointing to the minimum necessary to keep the wall (or stack) in a weatherproof and safe and sound condition.

Do Take great care to match replacement bricks and mortar with existing wall.

Do Use small hand held (non power) tools to carefully take out decayed joints or pointing avoiding damage to the historic brickwork.

Do Use well graded sand usually including some coarsesharp aggregate to match the texture of existing historic mortars.

Do Carefully match existing pointing or jointing profile and finish.

Do seek advise or discuss proposed repairs or repointing with the EHDC Conservation Officer and/or an expert architect or surveyor, who specialises in historic building repair.

Do Enquire from the EHDC Conservation Officers whether grant assistance is available. It usually is, subject to the availability of funds.

Don't Use cement-based mortar for repointing and repair.

Don't Repoint whole walls when only a small area has failed or take down walls when it may be possible to carry out repair 'in situ'.

Don't Compromise and use readily available bricks or standard mortars which are not a very close match to the historic brick wall or stack.

Don't Use mechanical angle grinders to cut out resistant joints. If the joint or pointing is sound - leave well alone.

Don't Use 'off the shelf' builders sand for all of the aggregate in mortar.

Don't Use harsh and jarring standard modern pointing profile, such as weather struck pointing or bucket handle pointing or ribbon pointing.

Don't Rush into the repair of repointing of an old wall and use a cheap 'cowboy' builder who has no genuine knowledge or sympathy with historic building conservation. It must be remembered the unauthorised alterations to a listed building can be a serious criminal offence.

Bibliography

Society for the Protection of Ancient Buildings, Technical Pamphlet 5 - 'Pointing Stone and Brick Walling' G B A Williams 1986

S.P.A.B., Information Sheet 4 The Need for Old Buildings to "Breathe" Revised Philip Hughes 1987

S.P.A.B., Information Sheet 9 'An introduction to Building Limes' Michael Wingate 1988

English Heritage, Technical Handbook 'Practical Building Conservation'

Volume 2 'Brick, Terracotta and Earth'

Volume 3 'Mortars, Plasters and Renders' John and Nicola Ashurst 1988

English Heritage, Aspects of Conservation 3, 'The Repair of Historic Buildings: Advice on Principles and Methods' Christopher Bereton 1991

The Georgian Group, 'Georgian Brickwork', Guide No 2 1989

University of York, Institute of Advanced Architectural Studies, Research Notes 'the Conservation and Repair of Historic Brickwork' 1990

Rose of Jericho Limited, suppliers of lime putty and lime mortars, Information Sheet 'The Strength of Ordinary Mortars' 1991

Grant Aid and Further Advice

Fine old brick walls are to be valued highly and should be cherished by us all as custodians for future generations. 'We are only trustees for those that come after us'. The repair and repointing of old brick walls and chimney stacks is usually eligible for a Historic Building Grant. If you need any further information regarding grant aid or general advice, please telephone:

The Conservation Officer in the Planning Department
East Hertfordshire District Council
(01279) 655261 extension 436

Or write to:

Development Control (Conservation)
East Herts District Council
Wallfields, Pegs Lane
Hertford
Herts SG13 8EQ

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Brick Repointing and Repair

Introduction