Category BRICKWORK BRICKLAYING

Tying in a new junction wall, particularly if it is for a large extension, can be very labour-intensive and time-consuming. A quick, simple and cost-effective alternative is the use of a ‘wall-starter’ system. There are
various versions on the market but the basic principle for all of them is much the same. Wall starters comprise two basic components: a metal channel or profile (usually stainless steel) and a set of metal ties. The profile is rawl-bolted vertically to the existing wall where the junction wall is to be joined on. Profiles come in individual lengths, from 900mm to 2m, depending on the manufacturer, and can be cut as required and/or clipped together to tie in junction walls of up to three storeys in height. Usually, one vertical profile is required for every half-brick thickness of the junction wall. The corresponding metal wall ties clip into the channel and are bedded at regular intervals into the bed joints of the junction wall as it is constructed.

As well as being quick, easy and cheaper, wall starters make it easy to tie in new brickwork of 75mm gauge to old existing walls of a different gauge that make use of bigger bricks and thinner bed joints. The only real downside is the fact that wall starters create a continuous vertical 10mm joint throughout the height of the junction and some find this unattractive. Others, however, can live with a straight joint, and are happy to make the compromise in order to save the extra time, effort and cost of cutting indents in the face of the existing wall. The straight vertical joint is usually either pointed and jointed with mortar or sealed with mastic.

Again, when constructing extensions or making internal alterations, there is often a need to tie in a new wall at a 90-degree angle to an existing wall, in the form of a junction wall. Toothing-in and block bonding (see above) can be used for this purpose – the only essential difference is that the indents have to be cut into the face of the existing wall in order to tie in the new junction wall.

The first task is to mark out accurately on the existing wall the positions of the toothings or block indents to be cut out. When marking out, allow for an indent that is 25mm wider than the brick or block to be let in and take care to ensure that the indents are all vertically aligned. Having marked out the indents, the cutting process will be greatly aided by drilling and removing as much as possible of the mortar joints adjacent to the brickwork being removed (indicated by the solid red marking-out line). Where broken marking-out lines cross through bricks, these are the points at which bricks must be firmly marked with a hammer and sharp bolster chisel. This process will ensure a neat edge to the indent when chopping out is complete, which is most important when the finished work will be visible, such as when cutting toothings on facing work.

When chopping out an indent, start from the middle using a lump hammer and sharp cold chisel and work outwards, taking care not to damage the adjacent bricks when the
outside edges of the indent are reached. Working from the outside in to the middle will result in damage to the bricks that surround the indent. When a clean edge has been achieved in the middle of the indent, it is then possible to continue chopping out with a narrow, sharp bolster instead of the cold chisel.

Block bonding is similar in principle and practical methods to toothing but involves cutting out indentations into the end of the wall that are either three (minimum) or five (maximum) courses high. Using this method ensures that each indent achieves an optimum number of tie bricks. Block bonding is a little quicker and easier than toothing and tends to be used to extend unseen work, where adequate strength is still needed but the aesthetics of accurate or normal bonding are less important.

The depth of the indents cut into the existing wall will, again, depend on the existing bonding arrangement. For quarter-bond walls the depth of the indent will be 56mm and for stretcher bond, 112mm. When bonding in the new brickwork at the first course of each indent it is considered good practice to insert mesh reinforcement or wall ties, for additional strength at the junction between the new and old brickwork.

When constructing extensions or making internal alterations, there may be a need to extend the length of an existing wall. There are two recognized methods for this.

Toothing

Toothing involves cutting out every alternate brick at the stopped-end of a wall in order to build on new brickwork and continue the bonding arrangement through from the existing wall into the new section. For this reason, toothing is favoured as a method for extending walls on facing work, where the bonding arrangement will be visible and must be seen to be a continuation of the original wall.

The depth of the toothed indents cut into the existing wall will depend on the existing bonding arrangement. For quarter-bond walls the depth of the indent will be 56mm (a quarter-brick + 10mm cross-joint); for stretcher bond the depth will be 112mm (a half-brick + 10mm cross-joint).

Toothed indents should be cut into the wall working from the top down, to avoid any risk of breaking off the projecting tails of the existing bricks. The method of cutting out starts with drilling the mortar joints around the bricks to be removed and is essentially the same as for replacing perished bricks. When all the bricks and mortar have been removed the indents should be brushed out to remove any dust.

Before any new construction starts, it is vital to acquire bricks that are the same as those in the existing wall. In addition, the mortar being used for the new brickwork should match that used in the existing wall, in terms of both strength and colour. The projecting tails of the toothing on the existing wall should be checked for plumb, to establish whether any cutting is needed when joining up the new brickwork to the old – hopefully there will be no deviation. If any is present, it will be small and can be accommodated with slight adjustment to the cross-joints of the new brickwork without the need for cutting. Finally, dampen the toothing with water, to ensure good adhesion for the new mortar.

When building away from toothings, the far end of the new wall should be set up and then the brickwork should be run-in between it and the toothings, using a string-line to ensure horizontal alignment. The string-line will most likely need to be attached to the face of the wall with a pin knocked into the mortar joints. (This will need to be made good with mortar when the work is completed.) Every tie brick (the brick inserted into the toothed indent) on alternate courses must be the first brick laid in that course and never the last. This is vital to provide the opportunity to get a full cross-joint inside the indent and to enable the bed joint above the tie brick to be caulked up solidly with mortar under the projecting tail of the existing brick above. Caulking up solidly at this point is best done using a semi-stiff mortar that can be compacted into the joint without squeezing out. Failure to achieve solid joints where

new brickwork joins to old will result in a weak point within the wall.

Re-pointing work should be carried out only in favourable weather conditions – never in wet or frosty weather or when rain or a frost is expected.

After raking out the old mortar, and in readiness for re-pointing, all dust and debris must be removed from the joints with a brush. Any left behind will interfere with the ability of the new mortar to bond into the existing brickwork. To ensure good adhesion for the new mortar, dampen the raked-out joints with a wet brush or a fine water spray, making sure that both the edges of the bricks and the old mortar are damp. The wall must not be too wet or saturated as this would lead to mortar stains on the brickwork when applying the new mortar to the joints.

For small areas of brickwork, the brick trowel blade can be loaded with pointing mortar but for larger areas its is recommended to use a hand-hawk, which can hold more mortar.

Fig. 270 Hand-hawk.

Whichever tool is being used to hold the mortar, the back of a pointing trowel is used to flatten an area of the mortar with a ‘patting action’, to a thickness of around 10mm (the width of a mortar joint) and with a fairly straight edge at the front. Patting the mortar in this way also helps the mortar adhere to the brick trowel or hand-hawk.

The process of filling the joints with mortar has four distinct steps (see Fig 271): Always starts with bed joints followed by cross-joints. Work downwards from the top of the wall, concentrating on an area of approximately 1 square metre of walling at a time.

1. Tilt the hand-hawk away from the wall and use the long inside edge of the pointing trowel blade to cut away a piece of mortar around 15mm thick (in other words, the raked-out depth to be filled) from the front of the flattened mortar. As part of the same movement, move the trowel towards the wall, while at the same time pulling the hawk away from the wall. There will now be a narrow strip of mortar on the edge of the trowel. The cutting action needs to be quick in order to ensure that the strip of mortar sticks to the back edge of the pointing trowel. When re-pointing cross-joints, the strip of mortar needs to be cut off at a length of around 65mm, to fit the height of the cross-joint and to avoid staining the brick above and below the cross-joint. Mortar that is cut off for bed joints can make use of the full length of the edge of the pointing trowel blade.

2. Keeping the trowel at an angle, move the mortar towards the joint to be filled.

3. Firmly push the mortar into the raked-out joint and, using a twisting action of the wrist, pull the mortar against the most convenient arris of the brickwork to one side (for cross-joints) or to the edge above or below (for bed joints), to ‘clean’ the back of the pointing trowel and to release the pointing mortar from it. Pull the pointing trowel away. (The choice of arris used for this purpose is not important – it will change numerous times during the course of the work and depends greatly on the left – or right-handedness of the bricklayer and whether he or she is working above head height or at low level.

4. To avoid staining the brickwork during re-pointing, keep the back of the pointing trowel clean by scraping it on the edge of the hand-hawk. With the empty pointing trowel, repeat the process to build up the correct amount of mortar in the joint.

When an area has been re-pointed, apply a joint finish to the new mortar; see Chapter 10.

The mortar used for re-pointing should generally match the strength of the bricks and be a mix of cement, lime and sand. Suggested mix proportions for most applications would be 1:2:8. Walling that is more exposed to the weather would probably require a stronger mix, such as 1:1:6. Avoid using a harsh sand/cement mix that omits lime, as the mortar will set too quickly and will form a weak bond with the bricks that is easily loosened by frost. As with all mortars, the mix proportions must be accurately and consistently gauged to ensure uniformity of colour and strength.

Colour of mortar can be an important issue, particularly if only a portion of a wall is being

re-pointed, and the new mortar needs to match the existing, adjacent mortar. This is sometimes referred to a ‘patch pointing’. Choice of sand has a direct influence on colour, with red sand producing a brown mortar and yellow sand producing a grey mortar. However, it may be necessary to introduce colouring additives in order to get the match as close as possible. This kind of detailed work is likely to be within the context of a historic and/or listed building and may even involve building a small temporary wall with raked-out joints (a sample panel), in order to test the colour match of the new mortar. Where listed buildings or buildings in conservation areas are concerned, it is quite common for the relevant Local Authority to specify the building of a sample panel in order to agree the mortar mix and colour to be used.

From a practical point of view, the water content of the mortar needs to be less for re-pointing than for bricklaying, simply because such a level of workability is not required or desired. The mortar for re-pointing must be firm enough to be cut into strips that will adhere to a pointing trowel and maintain their shape for long enough to be inserted into the joint, and then to receive a joint finish within a short period of time. If it is too wet, it will be difficult to push the mortar into the joints without staining the brickwork. The mortar will then have to be left for a period of time to ‘go off’ before a joint finish can be applied. As a test of consistency, the mortar should stand up on the pointing trowel without sagging.

Re-pointing is a slow, time-consuming process so only small amounts of mortar should be mixed at a time, otherwise it will start to go off before it is used. Batches of approximately half a bucketful are usually sufficient.

The only solution is to remove the degraded mortar to a depth of at least 15mm and re-point the brickwork with new mortar. Removal of the old mortar between joints must be done carefully in order to avoid damage to the arrises of the bricks. A hammer and plugging chisel are preferred to an angle grinder, particularly on very old buildings, where the bricks are comparatively soft, and under-fired in many cases. Very soft mortar can probably be removed with an old flat-head screwdriver. Where joints are particularly narrow, as is often the case on very old brickwork, it may be necessary to remove the mortar with the blade of a masonry saw. While a small-bladed angle grinder undoubtedly provides the fastest method of mortar removal, it is difficult to keep the grinder aligned with the joints and the chance of damaging the brickwork is very high, so raking out by hand should be favoured wherever possible.

When raking out, work downwards from the top of the wall and work on approximately three courses of bricks at a time. Always remove the mortar from cross-joints first, followed by the bed joints. If the bed joints are removed first, there is a risk of chipping into the bricks above or below when one comes to clear the vertical cross-joints.

The long-term success of raking out and repointing depends enormously on achieving a raked-out depth of at least 15mm and making sure that all the mortar has been removed from the edges of the bricks inside the joints. Failure to do this will result in poor adhesion and the new mortar being susceptible to the action of frost; it could simply ‘pop out’ after only one winter. Undertaking re-pointing but failing to rake out properly, or to a sufficient depth is, therefore, a waste of time and effort! Where mortar is found to be loose and degraded beyond a depth of 15mm, it should be cleaned back until reasonably firm mortar is located.

Over long periods of time and prolonged exposure to the weather, mortar joints begin to deteriorate. This is more prevalent on old walls or buildings, which are likely to have been constructed with softer lime mortar and/or weaker mortar mixes. With successive winters, the mortar begins to succumb to the actions of frost, which causes the front of the joints to crumble and fall away. If left unattended, the mortar joints can deteriorate to the point where rain
penetration through the wall becomes an issue, as does the risk of structural failure.

One of the most common problems associated with bricks and brickwork is that of ‘spalling’ or ‘spelching’, long after construction has been completed. This may be caused by frost damage – water in the brick freezes and then expands, and this can force the face off the brick (see Fig 267). A less common cause is crypto-efflorescence, but the net effect is the same. This kind of damage is most prevalent in brickwork below DPC level, on very exposed walls or on free-standing walls where rainwater is not thrown clear by the coping and simply runs down the wall face.

As part of the maintenance of external walls, it may be necessary to cut out and replace individual bricks or small areas of brickwork that have suffered spalling. The removal of damaged bricks is usually achieved by chopping out the mortar joints that surround them using a lump hammer and a sharp plugging chisel. This process is made much quicker and easier, particularly on cavity walls, by drilling holes through the mortar joints at frequent intervals with an 8mm masonry drill bit. Damage to surrounding bricks should be avoided as far as possible, which is why it is not a good idea to use anything bigger than an 8mm bit or a heavy-handed tool such as a cold chisel.

Replacement bricks should, obviously, match the existing brickwork and the new mortar should be of the same mix as the original. Any significant difference in the mix proportions between new and old mortar could result in differential movement and cracking. From an aesthetic point of view it should be noted that an invisible repair will be impossible due to introducing new materials into a wall that has weathered and, therefore, changed colour somewhat over time.

Having removed the old bricks and mortar, ensure that all the dust and debris has been removed and dampen the area with water to ensure good adhesion for the new mortar.

When replacing an individual brick, or indeed the last brick in a group, it can be difficult to achieve a tight fit and a compact and full mortar joint on top of that brick. This is most significant when repairing a cavity wall since there is nothing but air behind the brick against which to ‘pin’ the new mortar for the top joint, and pointing mortar simply falls into the cavity. To overcome the problem, it is necessary, having positioned the last brick, to ‘caulk up’ the top joint with pieces of slate. This ensures a strong, tight fit and allows the joint to be pointed up easily. At all times, care must be taken to ensure that no debris falls into the cavity.

The situation is much easier when replacing bricks at the front of a solid wall that is one brick thick or more. In order to achieve a tight joint at the top of the new or last brick, it is necessary to excessively butter the back of the brick with mortar and to force the brick into the opening. This is best achieved with a wooden or rubber mallet that will not damage the face of the brick. As the brick is forced in, the mortar at the back gets squeezed forward over the top of the brick – the mortar needs to have a high degree of workability for this to be effective. A tight joint should then be achievable with some final pointing up, without the need for any additional caulking up with slate.

For free-standing walls, there is a second option for replacing damaged brickwork. It may be economically viable partially to take down the wall to the point where the defective brick/s occur, utilizing the principle of racking back, to renew the defective brick/s and then to rebuild the wall back up. A value judgement would need to be made on a case-by-case basis as to whether such a course of action is practical, since the lower down the wall the defective bricks are located, the more significant the amount of brickwork that needs to be taken down. The time and cost of rebuilding must also be taken into consideration. If any original bricks are to be reused, they must be cleaned of old mortar (‘dressed’), which will demand more time, and will further impact on any decision relating to viability.

Mortar bees (or masonry bees) are so called because they sometimes burrow into the soft mortar joints of old brick walls. There are a number of different species of bee that do this, but the most common has the scientific name of Osmia Rufa. In appearance it is rather like a small version of the ordinary honey bee but a little more hairy. Being small, they are often mistaken for wasps, but they are soft brown and yellow coloration rather than bright yellow and black.

The natural habitat of the mortar bee is earth banks and soft exposed rocks into which the female bee burrows a small chamber (approximately 20mm deep), to lay her eggs. Some species (often referred to as miner bees) can excavate much deeper to form more complex tunnels and galleries. Soft mortar in old brickwork makes an ideal, alternative nesting site. Contrary to popular belief, mortar bees do not eat the mortar, but merely excavate into it. Tell-tale signs of activity are small piles of mortar dust at the base of the wall. Mortar bees will also lay eggs in old drilled holes in brickwork, gaps around window or door frames, holes in airbricks and even redundant key holes. When nesting in brickwork, mortar bees are most likely to make use of south-facing walls that receive sun for most of the day.

The adult bees live for a short period of time (approximately April to July), with only one brood raised each year and nesting taking place in early spring. The bees lay their eggs in their chambers, which they also stock with pollen and nectar, following which the chamber is sealed. The eggs hatch out as larvae that feed on the pollen and nectar left in the chamber. The larvae then pupate and subsequently hatch out as bees, which emerge from the chamber.

Mortar bees are solitary creatures that, unlike honey bees or wasps, do not form social colonies. They do, however, exploit the same suitable nesting sites, giving a false impression of a larger colony. They are not aggressive, and pay little or no attention to people. They have a sting that is unable to pierce the human skin and is therefore harmless and, like all bees, are beneficial as pollinators of plants.

In terms of preventive measures, the spraying of insecticide is generally ineffective as the bees are found only on sunny elevations and insecticides break down with UV light. Moreover, the eggs are sealed inside the chambers so are protected from the insecticide. The only effective way of preventing these bees is to re-point areas of soft and perished mortar, as the bees are able to burrow only into comparatively weak materials. This work is best done in late summer or early autumn, once the bees have ceased their activities but before winter sets in, which can cause more damage to the masonry.