Brick slip systems are being installed in vast areas on high rise buildings across the land, to a height of over 20 stories

Arup’s Alexis Harrison

feature large overhanging soffits. But are these systems safe, and should we be concerned about their long term robustness? There are a dozen or so proprietary brick slip systems on the market in the UK, most of which have emerged in the last five to 15 years. The majority of systems began as a means of upgrading the insulation on existing low-rise housing stock – insulation could be applied to the outside of say, a terrace of brick houses, and slips could be bonded to the insulation face to reinstate the neighbour- hood characteristic. More recently, as new-build high rise brick buildings have become increasingly popular, the system manufac- turers are keen to get in on the action, even though such systems may never have been designed for use on tall buildings, with their increased exposure and serious hazards if slips should fall.

Adhesives and testing

Almost all brick slip systems rely on the adhesive bond of bricks slips onto a rigid substrate – these vary from plastic sheets, insula- tion boards, cement particle boards and steel sheets. Some provide a robust mechanical interlock which retains the slip should the adhesive bond ever fail, via either metal fixings or by casting dovetailed slots into thin, high performance concretes. The majority of systems however, rely entirely on adhesives.

Manufacturers and their agents are quick to point out the proven performance of adhesives, backed up with data sheets and independent tests showing huge bond strengths which only ever fail with a cohesive failure of the slip (whereby the adhesive is stronger than the slip). Likewise, our attention is often drawn to adhesive technology in automotive and aeronautical applications. But the lifespan of performance cars, planes and spacecraft is relatively short, and rigorous and regular inspections are undertaken. Buildings (especially towers) are often neglected for years due to difficult access, and frequently exceed their design life by decades. Recent research by Arup has identified the potential for failure modes in adhesively bonded brick slip systems due to deterioration of the adhesive and/or its interfaces. For example, many adhesives are known to lose their ductility over time, meaning that they become brittle with age and have less capacity to accommodate movement of the system components. Most bricks are porous, allowing moisture and air to the interface between the adhesive and the slip. Hydrolysis and oxidation are just two of the mechanisms that can deteriorate adhesive bonds over time. Accommodation of movement is an essential consideration in any facade system as the materials will be subject to thermal and moisture expansion through endless cycles of day and night,



Maccreanor Lavington’s Cartwright Gardens is a student halls scheme in the heart of central London – it has a finely crafted brick facade using precast panels that “looks nothing like a unitised system”

summer and winter. Each material has a different rate of expansion, some considerably so, and the adhesives have to take up the differ- ence, leading to the potential of long-term fatigue. Additionally a facade is subjected to long term cyclical loads, such as positive and negative wind load deflections, and deflections in the primary structure under live loads.

Considering the high risk of serious injury if failure occurs, there is little evidence of adhesive-only brick slip systems being tested to verify that they avoid these known failure mechanisms. Most come with certificates from independent authorities, detailing multiple tests that have been undertaken, but there is no product standard that ensures a system will be durable. These certificates are accepted by building control officers, government departments and insurers, leading to the assumption that the systems are suitable for their application, and so adhesively-fixed brick slip systems have crept into the common language of building facades. These concerns need to be seriously considered when specifying a brick slip system which relies entirely on adhesives ,where falling slips could be hazardous. It is too soon to judge from track record alone how such systems will perform in the long term, and we are yet to see sufficient evidence from testing. Until such time, my approach is to specify brick slip systems with robust mechanical connections.

Alexis Harrison is a designer at Arup specialising in clay and ceramic materials –


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36