In this blog, Icon Surveyors will look at three types of property walls, namely a ‘Rubble Wall’, a ‘Solid Brick Wall’ and ‘Cavity Wall’.
The first wall that we are going to look at...
“Rubble masonry is rough, uneven building stone set in mortar, but not laid in regular courses. It may appear as the outer surface of a wall or may fill the core of a wall which is faced with unit masonries such as brick or ashlar. Analogously, some medieval cathedral walls are the outer shells of ‘ashler’ with an inner backfill of mortar-less rubble and dirt.” (Ashler; a block of hewn stone with straight edges)
The oldest form of this kind of masonry dates back to 2900-2600 BC when the Egyptian’s built the 14 meters high, Sadd el-Khafara dam. It was made using sack masonry that was built as an embankment covered with boards, stones or bricks. This coating was used to both strengthen the embankment and make it more difficult for any enemy to climb.
During the 1700s, as a result of a number of improvements in brick making such as blending clays better moulding techniques and more even firing, bricks shapes, consistencies and sizes were far better than those of the popular red and purple coloured bricks used in the 1600s. 1784 saw the end of the American Civil War of Independence. To pay for the war, King George 111, introduced a brick tax together with drains pipe and tile taxes. Brick tax initially cost a brick manufacturer 2s and 6d per thousand bricks going up to 5s and 10d by 1805. Needless to say, this had a devastating effect on minor brick producers who were forced out of business as a result of having to sell their stock to pay the taxes. Thus, both the use and quality of bricks in construction declined until 1850 when the brick tax laws were repealed.
Brick walls can either be solid, in other words, there is no gap between the interior and exterior walls, or, cavity walls where a gap between the exterior and interior wall exists. An important element of constructing a brick wall is how it is bonded, in other words, which structural pattern is formed from the bricks. This determines not only the aesthetic look of the building but more importantly, how the bricks react to and protect the building from the natural elements.
Icon Surveyors will mention two types of brick bonding in this blog, these are the English Bond and the Flemish Bond. Brick bonding is the structure or pattern in which the bricks are arranged. These are configured using headers and stretchers. A header is a brick that is laid flat with its width exposed and a stretcher is a brick that is laid flat with its long narrow side exposed.
The English Bond
“English bond is composed of alternate courses of headers and stretchers. The headers are centred on the stretchers and joints between stretchers in all courses are aligned vertically. Snap headers are used in courses which are not structural bonding courses.”(gobrick.com)
With Flemish bonds,
“Each course of brick consists of alternate stretchers and headers, with the headers in alternate courses centred over the stretchers in the intervening courses. Where the headers are not used for the structural bonding, they may be obtained by using half brick called “clipped” or “snap” headers. Flemish bond may be varied by increasing the number of stretchers between headers in each course. If there are three stretchers alternating with a header, it is known as a ‘garden wall’ bond. There are two stretchers between headers, it is designated as a ‘double stretcher garden wall’ bond. ‘Garden Wall’ bond may also be laid with four or even five stretchers between the headers.”(gobrick.com)
Flemish bonding was used a lot in England from the 1700s through to the 1920s. Houses built using this method were designed to provide solid walls that could breathe, thus keeping the house at a healthy temperature and from being exposed to too much moisture from the natural elements. In many of the properties built during this period, air bricks were used to produce ventilation to the interior of the property, as a result of which, a flexible lime mortar is, more often than not, used to repair the mortar joints between the bricks or other masonry elements.
The objective today is to ensure that homes are built to reduce the occupant’s carbon footprint thus, for a property to be carbon-efficient it must be as air and watertight as possible.
Common Problems in Brick Walls
One of the most common problems that arise with solid brick walls is using an incorrect mortar when pointing (repairing) the joints between the bricks. The mortar is a bonding agent used between the bricks and is usually made with a mixture of lime and cement or a combination of both with sand and water. When these properties were built between 1700 and 1920, the most likely mortar used was lime and cement. The high concentration of lime would enable the building to breathe.
However, mortars used today are not as flexible or breathable, meaning that walls ability to self-control the moisture and temperature from the natural elements are obstructed, as the water is contained in the brickwork for longer periods of time enabling it to travel to the interior wall, these walls become damp causing damage to the interior wall and its decorative state. This can also happen when any trapped water becomes frozen, thus expanding the brickwork, causing damage to the exterior walls.
Bridged Damp Proof Course
Water ingress can cause a multitude of problems; this is usually resolved by installing a damp proof course (DPC). A damp proof course is a layer of waterproof material that is bedded between a course of bricks that have been laid 3-4 courses above ground level. It acts to prevent any water from rising up the brickwork and penetrating through to the internal wall. However, as the building gets older and new installations including patios and driveways are built, the damp proof course weakens enabling water to ingress up the brickwork and in some instances causing it to travel to the interior wall. This is usually fixed by reducing the ground level.
The construction of cavity walls is usually in two layers, using blockwork and brickwork. There is a gap between the layers which can be between 90-120mm. the gap helps with the weatherproofing of the building and increases the thermal capabilities of the wall. The layers are bound together by wall ties or steel wire also known as ‘leaves’ or ‘skins’ to support the structure of the building. Cavity walls are designed to ensure the external leaf is both non-load-bearing and weatherproof and functions is to protect the building from the natural elements and provide a tough long-term exterior finish. The interior leaf is used to provide insulation thermal efficiency.
These types of walls are usually constructed in areas that are exposed to regular wet and windy weather conditions. The cavity wall is built to function as a drainage system for water that may penetrate through the external brickwork. Instead of seeping through the interior wall, the water runs down the inside of the wall and into the ground.
Today, cavity walls are very popular in that the materials that can be used for insulation purposes whilst increasing thermal capabilities can also reduce the carbon footprint of the building.
A Common Defect in Cavity Walls
Wall Tie Failure
One issue that can be seriously problematic and costly is wall tie failure. As described above, external and internal cavity walls are held together using wall ties or steel wire. Problems arise when for whatever reason, be it deterioration due to age or failure to install or protect the ties or steel wire adequately, it erodes causing it to expand up to several times its original size. The result of such expansion can cause cracks in the mortar (bonding agent), leading to less protection from water penetration, which in the most severe case can cause cavity wall failure. As the fundamental purpose of the wall ties is structural support, effectively corrosion of the ties could cause the structure to be less sturdy or even the collapse of either of the walls.
Properties most at risk of this problem are those built between 1935 and 1981. This is because the ties were not durable enough causing them to corrode more easily. Another common cause of wall tie corrosion is when the builders drop small amounts of mortar over the wall ties enabling any ingress of water to travel along with the mortar and into the internal leaf of the cavity wall. This can lead to the interior walls of the building becoming damp.
If any of the matters raised in this blog concern you, our experienced party wall surveyors would be happy to assist.
Note*: This blog is not an authoritative interpretation of the law; it is intended as a general guide.