How a survey of a building complex discovered issues and failings related to cladding panels constructed of aerated concrete.

The design and engineering stages of a building can often be overwhelming, with the variety of options available to engineers, designers and builders. We are constantly faced with new products and systems that are developed, approved and introduced to the market, often with a range of benefits and cost savings that make it hard to ignore. Unfortunately, some of these products were originally tested and approved to perform as per the relevant building codes but don’t always perform as originally intended.

A recent Building Survey completed by Hampton Jones has found critical problems with a building where the external wall cladding is an aerated concrete panel. Though the aerated concrete has a range of benefits and applications that work well in some areas of the country (particular to added insulation), it did not yield the same results in this building complex that is sited within proximity to a sea spray zone.
This cladding system has design inclusion of an enclosed cavity system (different to a conventional drained and ventilated system). The cladding panels are screw fixed onto horizontally run metal cavity battens. These are attached through the wall underlay via screw fixings to the internal timber framing. The cladding is a porous material, coated with a breathable paint finish, designed to naturally release moisture that enters the closed cavity back through the external face of the cladding. Due to the lack of maintenance to the paint and cracking to the horizontal and vertical panel junctions, excess moisture entering the system became trapped and compromised the original design of addressing moisture entering the enclosed cavity via evaporation.

The excess moisture trapped within the cladding, increased the overall weight of the aerated concrete. Additionally, the horizontal metal battens in the cavity system were found to be trapping and holding moisture that reached the back face of the cladding, resulting in advanced corrosion to both the cavity batten and screw fixings. The original fixing design did not account for the additional weight of the absorbed water and corrosion to these fixings. Therefore, Hampton Jones believes this to be a potential Health and Safety concern due to the increased likelihood of panels detaching from the walls due to negative wind pressures, when exposed to inclement weather and/or seismic movements.

Cladding panels were removed for further investigation. This revealed:

• Extensive mould deposits to the back faces and base of panels.
• The cavity, when opened, was found to contain trapped warm humid air.
• Corrosion to the steel columns of the structural frame in some locations.
• Corrosion of the reinforcement bars within the panels themselves. (Steel expands when it corrodes and this can cause cracking and damage to the panels, including allowing further water ingress that will exacerbate the problem.
• In most locations observed, the supporting timber framing behind the cavity appeared to have limited water damage.

The cladding product does have benefits and reasoning around its unique design and has been seen to perform in other locations. However, this investigation demonstrates that it is vitally important to ensure all manufacturers’ recommendations are strictly followed during design and installation. All factors need to be considered, including the geographical location of the building, as the climate also plays a role in the performance and lifespan of this aerated concrete application.
Another crucial recommendation for this aerated cladding system is that a very specific type of breathable acrylic paint must be used on the cladding for the moisture to be released naturally. This might seem like a reasonable expectation, however, if the painter was not made aware of this type of application there would not be much consideration for the specific paint application options. This would impair the release of trapped moisture contained within the aerated concrete cladding. It is also vitally important to ensure that the paint coating is regularly maintained and recoated in a like for like material.

Without a thorough investigation, many of these issues might have been missed since the internal walls did not show significant damage occurring to the building structure. (Normally observed and alerting occupants and owners of issues that need addressing). This is an example of why Hampton Jones’ team of Chartered and Registered Building Surveyors, have the skills and technical expertise to carry out thorough investigations of building defects. We provide solid reasoned advice to clients on remedial options for repairs and for ongoing long-term maintenance. This results in better building and better lives for building occupants.

Let Hampton Jones help you give your building brilliant performance and let you live better lives.