POINTING (OR JOINTING) OF BRICKWORK
1.00 HISTORICAL NOTE
1.01 Although many of the early Suburb cottages were rendered or pebbledashed, and some of the later "Modern Movement" houses are also rendered, the majority of houses are in facing brick. Even the rendered houses often have facing brick plinths or chimneystacks. The facing brickwork is generally of a very high standard, and it is most important that this high quality workmanship is not destroyed by ill-considered repointing.
1.02 Most of the brickwork is laid in a lime mortar, which was the usual technique of the time. In frosty weather a certain amount of Portland cement might added to speed up the set. But the mortar is frequently quite soft and powdery, and people accustomed to modern cement mortars suppose that in some way it is defective.
1.03 It is not the intention of this paper to discuss the merits of pure lime or lime / cement mortars. The reader is referred to advice which can be read in many recent papers on the subject. Suffice it to say that a cement-rich mortar is definitely disadvantageous, particularly when used to re-point brickwork which has been built in a flexible lime mortar.
1.04 Most of the work was specified to be "cut off as the work proceeds." This means that the house was not pointed as a separate late operation. What you see is the mortar that the brickwork was built in. As the brick was laid and tapped down into line, the mortar was squeezed out at the joints. A diagonally upwards sweep of the trowel cuts off the protruding mortar leaving what is basically a flush, open-textured joint. With the passage of time, these joints have probably weathered back slightly. Certainly the aggregate material of the mortar will have become exposed.
1.05 Sometimes a "weather-struck joint" was used, running the trowel at a slight angle along the upper edge of the brick below the joint. Once again, the passage of time has softened the outlines and exposed the aggregate.
1.06 The weather-struck joint was used again in the 1930's by some Architects, often as a separate pointing operation, and sometimes using white cement and silver sand, to give a very white mortar.
1.07 Two types of pointing which are quite common today, were not used in the Suburb and must not be used in re-pointing.
1.08 The first is the "bucket-handle" or "hosepipe" joint. The action of tooling the joint produces a smooth dense surface which does not weather gracefully, but remains harsh and unchanging. The action also spreads the mortar over the arises of the bricks, giving a wider appearance which contrasts with the usual rather narrow joints of traditional Suburb work.
1.09 The second is the harsh weather-struck joint in which the lower edge of the bed joint actually projects in front of the brick face. This lower edge is then cut to a sharp straight edge. These joints have to be made in a dense smooth strong cement mortar, which is totally foreign to traditional work. Such pointing is actually detrimental to brickwork, particularly to the soft red bricks which are widely used in the Suburb.
1.10 We are aware of one house in the Suburb where tuck pointing has been used, apparently in original work. There are exceptions to every "rule" in the Suburb!
2.00 THE VISUAL EFFECT OF RE-POINTING
2.01 Original pointing is usually in an open-textured soft lime mortar which has weathered for up to ninety years. It is very difficult to match this when re-pointing is done.
2.02 The action of raking out the joints is liable to widen those joints, and such damage to the bricks cannot be repaired.
2.03 It is very rare that a contractor will use a pure lime mortar, and the most likely mix will be about (1:1:6) (cement:lime:sand). Great care is needed in making up a mix that will give a similar appearance to original work.
2.04 The action of pushing mortar into a raked-out joint is fundamentally different from cutting-off a protruding mortar joint, and great skill is necessary to simulate existing work.
2.05 The colour of mortar makes a surprising difference to the apparent colour of the brickwork wall. It is therefore very important to get a good colour match. Look around and you will see semi-detached houses where one half has been re-pointed, with varying degrees of success or failure.
3.01 Because re-pointing can change the external appearance of the property so considerably (and also so unexpectedly) the Trust considers that Trust Consent is needed for both Freehold and Leasehold property. However, because we think it is such an important matter we do not charge a fee. You should also contact Barnet, particularly in the case of Listed Buildings.
3.02 If you are contemplating re-pointing a property, or if this course of action has been recommended or even required as a condition of a mortgage, you are asked to contact the Trust urgently.
3.03 A visit will be arranged to talk the matter over and advice will be given as to the amount of re-pointing, if any, which may be considered to be necessary.
3.04 If total or partial re-pointing is considered to be necessary the Trust will again visit to see samples of mortar for colour, texture and pointing style. This discussion should really take place with the Contractor, or indeed the "man with the trowel in his hand".
3.05 Where an extension is being built, or brickwork alterations are being made there is again a need to make a good match to original work for both the pointing and the bricks.
3.06 Obviously wet mortar is a completely different colour from dry mortar, and it is quite useless to be called out to see some wet mortar and approve it for colour.
3.07 Architects or Contractors will often have a square metre or so of brickwork pointed up or a new brick panel made. Both of these will take a long time to dry out enough for the mortar colour to be assessed, perhaps weeks in the case of a new panel. If the colour turns out to be wrong, and perhaps the second sample is also unsuccessful, a serious problem of delay arises.
4.00 A BETTER TECHNIQUE FOR SAMPLES
4.01 We wish to see samples to assess pointing style, and also to assess mortar mix. These are two separate matters.
4.02 The pointing style can be examined by making a sample panel in the usual way, and can be assessed even if it has not fully dried out. Look at the original work in the building. This is what we have to match. As previously stated the profile is often a flush or very slightly recessed joint. This may be achieved by cutting off in the case of new work or by filling the joint with mortar (in the case of re-pointing) either by traditional trowel work or by modern techniques such as pressure feeding through a nozzle. Whatever the technique it is necessary that the joint shall have been well prepared and is well filled.
4.03 The mortar may have a smooth trowelled look at this stage. It is necessary to change this to a an open textured surface. There are many ways of doing this and we hesitate to be too dogmatic, because different bricklayers will have their own favourite techniques. It is very important to work cleanly, and mortar must not be smeared on the faces of the bricks. It is also necessary to judge by experience how much time should elapse for the mortar to go off to some degree before working on it. This time will be shorter in hot dry weather and longer in cool damp weather.
4.04 According to the amount the mortar has gone off and the personal preferences of the bricklayer, different methods can be used to impart the open texture. These can range from brushing or stippling with a soft brush, even a paint brush, through scraping with a stick, to scratching with a metal blade or two or three hacksaw blades tied together. A wire brush should not be used: this will scratch grooves in the mortar and may damage the bricks.
4.05 The more innovative technique is for making up samples to test for colour in about 20 minutes. If they are unsuccessful at first there is time to make several other samples, and we would claim that it should be possible to match the mix in the course of a morning. The equipment required is an empty yoghurt carton (or similar), a plastic bucket, a painter's hot air gun plus a selection of materials.
4.06 We will assume that the basic mix will be approximately (1:1:6) (cement:lime:sand). Using the yoghurt carton to measure the proportions accurately mix up a basic mix in a bucket. WRITE DOWN CAREFULLY THE PROPORTIONS AND THE MATERIALS USED IN THIS MIX. (It is useless if you get a perfect mix and then cannot remember how to make it again.) Tip the mix out on to a sheet of plywood or a spot board. DO NOT TOUCH IT WITH A TROWEL. (If you smooth it with a trowel you will bring water to the surface and the water will carry the cement and lime and alter the colour.) As you tip the mix out, smaller crumbs will fall to the side. Heat these with the hot air gun and they will dry out very quickly. Pick up a dry "crumb" and carry it over to the wall you are trying to match. Make the comparison and see whether you have been successful. If unsuccessful there are several variables.
4.07 Cement: a common fault is that the Portland cement has produced a dull grey mortar which kills all other colour. Different manufacturers produce cement with different degrees of greyness. You could try a different manufacturer. Alternatively most manufacturers make a "masonry cement" which is whiter in colour and probably contains plasticisers and other ingredients which are intended to improve performance. Or you can use white Portland cement, or a mixture of half white and half ordinary. Try another sample.
4.08 Lime is basically a white material, but you could vary the amount to some degree.
4.09 The major variable is the sand. A silver sand has very little colour. A soft builder's sand may impart a considerable amount of yellow, orange or brown colour. This is the sort of sand which discolours your hand when you pick up a wet handful. So the colour can be varied quite a lot by changing the sand.
4.10 Close examination of original mortars will often reveal an admixture of quite coarse material. This may be a coarse element in the sand, or may be that the original builders incorporated crushed brick (to improve the hydraulic characteristics of the lime) or other crushed material to impart other real or imagined advantages. In new work it is often advantageous to incorporate a proportion of a coarser sand. This will not only impart some character to the mortar, but will also help to tear open the surface when the pointing is finally brushed or scraped. Therefore the six parts of sand might consist of (say) four parts of a soft yellow sand and two parts of a sharper sand. Too much sharp material will make the mortar hard to use, but a "fatty" mortar can be restored by using a higher proportion of lime.
4.11 As a last resort a small amount of pigment could be used, but it is rarely necessary. Some specialist firms will deliver the lime and sand (coarse stuff) to site already mixed, with the cement to be added at the time of use, and they are often very skilful at producing the correct mix. But test samples should still be made as described previously.
4.12 This technique of making sample mixes is so easy and quick that there is no excuse for getting a bad match.
4.13 It is inevitable that new mortar will look harsh and raw. But it should be possible to do work which after six or twelve months will have toned down to be a-good match.
4.14 Weathered mortar will be dirty and stained black by soot, particularly in the case of chimneystacks. However it is a mistake to mix black pigment into the mortar to match this: such pigment is very dead-looking. Provided that the new mortar is open-textured it will soon begin to pick up dirt and weathering. Also the small indentations will create small specks of shadow, which will again darken the appearance. if, nevertheless, the mortar is unacceptably light and bright it can be toned down by dabbing with a soot and paraffin mix on the mortar.
5.00 GENERAL NOTE
5.01 These Design Guidance Leaflets are published by the New Hampstead Garden Suburb Trust Limited and are intended to give general background information and advice to Architects and others commissioned to design new work, alterations or extensions in the Suburb. They are not intended to be a substitute for employing proper professional advice, and they assume that the reader will have the necessary technical background and practical experience.
5.02 There is a wide variety of types of building in the Suburb and it is impossible to lay down a series of rules which will be applicable in all cases. Therefore the advice and hints which are given in this paper must be applied in a sensitive and thoughtful way. It will be possible to find an exception to almost every rule and statement. The designer should look around at the existing building or at others by the same architect. He should remember that alterations may have taken place since the building was built, and should not be misled into copying something which is not original.
5.03 The original drawings of Suburb buildings are often available from the Archive Trust. The Archive Trust is not part of the New Hampstead Garden Suburb Trust. For a fee a Xerox copy of the original can be sent to you. Access to the drawings is not available during school holidays.
5.04 The Trust Architect is always ready to discuss proposals or particular problems related to buildings, and give his best advice. It must however be clearly understood that all advice is given without prejudice to the decision of the Trust Council, either to grant or withhold Consent, or to impose conditions.
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