Brick masonry has been around for ages and continues to be a prominent building material today. Applications range from old mill buildings to modern building veneers. But while brick masonry is known for its strength and its outstanding performance, brick walls require consideration in terms of maintenance and upkeep.
There are four main ways to use bricks and blocks to make walls. Each method has its environmental and economic merits and it is important to understand the reasons for choosing any given method in building your home. It is quite feasible to use each method in the same home but generally more economical, logistically sound and environmentally effective to use just one or two.
Brick veneer — A commonly used approach in which bricks form the external skin of a timber framed home
Reverse brick veneer — Bricks form the internal skin of an insulated, framed home
Double brick — Consists of two leaves of brickwork with a cavity
Solid brick — A high thermal mass construction mostly used for internal walls
Good detailing for brick and blockwork needs to incorporate the damp-proof courses, flashings and weep holes. [2] The following are some of the common brick engineering problems that we tend to experience in Perth:
Parapets
Parapets are one of the most failure susceptible building features. Wind loads can be extremely high on parapets as they receive wind loading from two directions (front and back). Wind-driven rain can also cause problems to parapets from both directions.
Brick parapets can start to tilt for several reasons. Older brick and mortars are highly susceptible to moisture expansion. Over time, if one face of the wall continues to get wet and does not dry as much as the other side, the parapet can expand upward while the other side does not expand or expands less. This will eventually result in a pronounced curving parapet. Unlike brick walls at or below the roof framing, there are no other structural elements to ‘hold’ an expanding parapet in place or to help resist any movements. The expansive forces from moisture and temperature can also act in the horizontal direction. Forces can build to a level where the parapet ‘buckles’ and bows (typically outward).
An equally troubling, source of faltering parapets is water intrusion from failed roofing flashing. Improper maintenance of roofs can lead to large amounts of water entering the cavities of a brick wall. Jacking forces from freeze/thaw can cause the wall to deteriorate and/or lean.
Both of these conditions will require some level of wall reconstruction. Proper flashing details and a regular maintenance/inspection program can minimize the extent of damage.
Paint/Coating failures
Brick walls can be thought of as hard sponges. Older brick masonry is traditionally more absorptive than new brick. Bricks can absorb rain water and then ideally release it back into the air (through evaporation) when the sun comes back out and relative humidity drops. This process requires that the brick can ‘breathe.’ The brick has to allow the release of the absorbed water.
When stripping paint it is important to be aware of all the potential hazards. Understanding the danger is the first step in minimizing the risks. One danger is from white lead, a white pigment which was commonly used as a component for oil-based paints until about 1950. For this reason it is
recommended to take special precautions when stripping oil-based paints. In uncertain cases it would be useful to have a sample of the paint removed and tested, to assess the presence and percentage of lead, before starting the paint removal job. Old bricks, being a rough porous material, hold paint very well and cannot be stripped with heat unless the layer of paint is thick and heavy. It may be best to leave the bricks alone or repaint them brick colour. It will prevent them from crumbling and save time and money
Coating brick with an improper product, e.g. a urethane-based coating, can cause a build-up of moisture in the wall. Pressure will form behind the coating and try to find its way out. Often, the pressure will be released by failure of the coating. Paint will peal from the building leaving large amounts of debris at the base. If the moisture remains trapped in the wall and temperatures drop, damage from freeze/thaw could occur.
Walls with improper coatings should be stripped using mild paint removers. In some cases, where portions of the coating are difficult to remove, soda blasting may be employed. All options should first be tested in a less obvious location where fine-tuning can occur.
Salt attack and raising damp
Salt attack and rising damp are two separate but interrelated processes; both must be understood if damage is to be minimised and if corrective measures are to be successful. While the term rising damp has been commonly used to cover both aspects, it tends to overlook the role of salt, an issue that will become increasingly important as our buildings get older and as our soils become more saline.
Rising damp is caused by capillary suction of the fine pores or voids that occur in all masonry materials. The capillaries draw water from the soils beneath a building against the force of gravity, leading to damp zones at the base of walls.
Many traditional buildings were constructed on footings of dense stone which helped reduce the upward passage of water. In modern construction rising damp is prevented by the insertion of a damp-proof course (DPC) which is generally a 0.5 mm thick sheet of polyethylene (plastic). Because many nineteenth century buildings were constructed without DPCs and because some DPCs have failed, been bridged, or damaged, there are now common problems of dampness at the base of walls. In most cases that dampness will have salt associated with it.
Salt attack is the decay of masonry materials such as stone, brick and mortar by soluble salts forming crystals within the pores of the masonry. As the salt crystals grow the masonry is disrupted and decays by fretting and loss of surface skins. The salt commonly comes from the soils beneath and is carried up into walls by rising damp. When the dampness evaporates from the walls the salts are left behind, slowly accumulating to the point where there are sufficient to cause damage. Repeated wetting and drying with seasonal changes leads to the cyclic precipitation of salts and the progressive decay of the masonry. [1]
Improper Repointing
It is disappointing to think about a well-intentioned property owner spending the money to repair a brick masonry wall by repointing it, only to have the repointing cause problems with the wall.
Mortars have improved immensely over the years. It used to be that brick was very strong and mortars were weak because the prominent and only available materials were lime mortars or natural cement. It wasn’t until the discovery of Portland cement did we achieve the ability to produce mortar strengths nearly as strong as concrete. In this case, stronger is not better. Older buildings lasted a long time because as foundations settled or strong winds blew against tall walls, the brick could absorb the movements due to the flexibility of the mortar. This mortar also acted as a sacrificial capillary pressure release.
We often see buildings that have undergone a repointing with severely damaged bricks.
Another repointing mistake is the use of rotary disc grinders to remove the outer layer of deteriorated mortar. This is more of a problem in older historic structures where mortar joints can sometimes be at thin as 5mm. Rotatory grinders can scar the surrounding brick forever damaging the look.
Unfortunately, it is hard to reverse damage due to improper repointing. Undamaged areas should be corrected as soon as this type of failure is identified. If the damage occurs in highly visible locations, it might be possible to harvest brick from less conspicuous areas. There is never a single answer for every project. Hiring a structural engineer familiar with material science is the surest method to both repair older buildings and prevent damage on new ones.
At Rotaru Building Consultants, we are structural engineers who can help you on your next brick restoration project or answer any questions you have about brick masonry engineering in general. As with any home purchase, be sure to get a thorough pre-purchase building inspection to see whether the house needs any repairs (blog image courtesy of The Times).
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[1] Salt attack and rising damp: A guide to salt damp in historic and older buildings. Heritage Council of NSW; Heritage Victoria, Department of Planning and Community Development; South Australian Department for Environment and Heritage; Adelaide City Council
[2] Your Home - Australia's guide to environmentally sustainable homes. Brickwork and blockwork
[3] Heritage Building Conservation Technical Advice Sheet 5 published by the City of Fremantle. Dealing with dampness in old walls