What is repointing?
Repointing Brick Walls is the restoration of decayed mortar joints in masonry walls. Repointing involves the careful preparation and filling of mortar joints with high quality materials. It is preferable to use mortar mixes that replicate the original mortar used during the period in which the masonry building was constructed. Helitec is dedicated not only to quality restorations but also to conservation principals.
The qualified masons at Helitec Structural Services have the highest level of skills needed to complete a satisfactory job of repointing. The craft of repointing might seem a straightforward operation, however our mason’s commitment to producing durable repointing procedures set us above the rest.
Mortar constitutes up to a quarter of the surface area of a bonded brick wall. Its colour, texture and appearance are greatly influenced by correctly pointed mortar. The rule of thumb is that if joints are eroded to a depth greater than their width they should be repointed. If the joints are further neglected water will penetrate the walling.
When assessing a historic building our engineers consider the scope of repointing necessary to reinstate its structural integrity. However tempting it is to repoint the whole building, when repointing a historical building consideration should be given to keeping as much of the actual walling as it is an archive representing the buildings past.
Sheltered areas under eaves, verandas and other less exposed areas should be preserved. Over time if correct matching is achieved the new works will blend with old mortar giving an attractive result.
The joints may be eroded in particularly exposed locations such as copings of parapets or on chimneys, or the damage might be due to other problems including faulty gutters, downpipes or rising damp. These problems should be addressed first, otherwise repointing will be a waste of time.
Possible forms of failure
Problems with mortar include spalling, crumbling, efflorescence, biological growth and cracking. These problems can be caused by frost, salt crystallisation, movement (e.g. settlement, wind, thermal expansion and contraction), environmental pollution (acid rain), water migration, and biological attack. Moisture is the environmental factor commonly associated with most of these problems, although temperature also has a significant influence on the rate and extent of damage caused by the moisture.
Sydney suburbs along the coast are susceptible to the corrosive effects of salt. Breakdown of the mortar joint allows moisture to invade the cavity between double brick walls and corrode galvanised brick ties. Rust can occur in other components of the building expanding steel reinforcements causing concrete spalling.
In extreme cases, due to long neglect, the erosion of brickwork joints is so widespread and severe that it threatens the structural stability of the whole building. Brick ties, window lintels, flashings and damp-proof courses and concrete elements may also require rectification or replacing. Cracked or bowed sections of brickwork may need to crack-stitched and strengthened with HeliBar reinforcement or sometimes partially or completely rebuilt.
The need to repaint wooden facias, windows and doors to protect against rooting is easily understood. The same principle applies to mortar joints and repointing can save from costly future repairs.
When selecting mortar or repointing brick walls
Helitec masons take into account the severity of the environment in which it will be used. The severity of the environment depends both on the local weather and the exposure of the masonry elements.
New South Wales has a large climatic diversity. Climates vary from hot summers to cold winters. Durable mortar mixes must reflect the environment of the building location. The original mortar mix used is closely inspected analysed and replicated if it has withstood the test of time or improved if it has shown to be less durable.
Helitec only use tested and proven ingredients when mixing repointing mortars.
When repointing brick walls the Helitec craftsmen understand the importance of materials used in creating durable repointing mortars. Our masons undertake extensive on-site tests to determine what is the ultimate mortar mix for the job.
Sand. Sand cleanliness, grading and particle shape are important factors in influencing the overall durability of the mortar mix. Sands with contaminants or a heavy clay content are rejected.
Sand is normally made up of particles with a range of sizes, the smaller sizes filling in spaces between the larger sizes. In well graded sands, the void space left over is assumed to be about one-third of the sand volume (the space varies depending on the sand particle shape and grading). Enough binder paste is then added to fill this void space and provide a film between the sand particles to give the fresh mortar plasticity.
Sands can come from natural deposits or are manufactured by crushing stone. In general, crushed sand is considered most angular (sharpest), while quarry sands vary from semi-angular to rounded. Although sharper sand makes the mix less workable, it provides more interlocking between particles reducing shrinkage. On the other hand, rounded sand particles are easier to compact into the joint and was often used in historic mortars. The easier compaction makes it more likely the joint is filled properly. The need for less pressure to fill the joint is also preferable from the masons’ point of view, reducing the risk of repetitive strain injury. Our qualified stonemasons are experts in mixing durable mortars.
Binders. The most common binders in mortar are lime and Portland cement. Lime in a mortar mix hardens by carbonation. Lime mortars take much longer to gain strength than Portland cement-based mortars. Mortars using Portland cements are stronger and gain their strength more rapidly which also meant construction can proceed faster. Also, mortars made from Portland become denser and less porous. They are therefore better at keeping water out, but should water get into the masonry it will also take much longer to dry out.
Binders can also be improved by admixtures. Helitec Structural Services adhere to Australian Masonry Standards AS 4773.2:2015 table 3.2 for all our mortar mixes. Admixtures may also be added to the mortar to change its colour, or improve workability, water retentivity, water repellence, bond with masonry units, and frost resistance.
The process of repointing brick walls is labour intensive. Each step of the process is critical for a satisfactory result in the cost, durability, and appearance of repointed mortar.
Joint preparation. The first step is the racking out of the deteriorated mortar bed. Raking out and cleaning of the joints must be carefully done to ensure no damage to the masonry units and that there is a clear rectangular space for the repointing mortar. Special dust control vacuum equipment is used which can eliminate 95% of the normal air-borne dust. Our operatives are clothed with necessary PPE. Helitec complies with Work Safe Australia requirements for workplace exposure standards for air-borne contaminants and the the Australian Standards AS/NZS 1715:2009 for the selection, use and maintenance of respiratory protective equipment.
The cardinal sin when repointing brick walls is widening the apparent joint width it distorts the overall appearance of the walling and will be difficult to rectify in the future. Thin joints are particularly difficult to repoint. Helitec undertake extensive quality control and supervision of our on-site operations to avoid disastrous mistakes that cause irreparable damage. Good contact between the repointing mortar and the masonry unit is vital. A uniform and even depth of 25mm is generally required.
The prepared joint is then rinsed with a low-pressure water jet and left damp but not wet then filling can start.
Mortar. Good compaction of the pointing mortar in the joint is important to good performance. For deeper joints it is usually done in more than one layer. The final finish of the mortar joint surface affects its water shedding capabilities. The surface should not extend out over the surface of the masonry units. Standard finishes range from a concave finish (best compaction and weather tightness) to a raked joint (worst). For historic masonry our masons are skilled in applying many other types finishes preferred by owners and project managers.
Joint profile. Once the joint is filled the surface is tooled to whatever profile is considered correct. What happens now determines the final appearance of the job but the tooling or ironing-in of the joint has a practical function as well as an aesthetic one. The action of compressing the face of the mortar closes the pores and gives it weather resistance.
Helitec have special tools for the different types repointing jobs. Jointers are made or modified to suit the particular joint widths present on the job.
Brickwork is routinely cleaned during the repointing works to reduce the need for additional harsher cleaning methods with high pressure water or concentrated acids which have detrimental effects on the brickwork unless done with great care.
Brick and stonework repointing can not only restore and refresh the appearance of the building but can also extend the service life of the building and help improve its structural integrity and protect against water penetration and save money on other costly emergency repairs and maintenance.
Environmental, material selection and workmanship all play a vital role ensuring satisfactory results.
Repointing needs to be undertaken by experienced and qualified trades people using only the quality materials and highest standards of workmanship.