Tremco has supplied some of the prestigious projects in the region including the Kingdom Centre.
Key to selecting correct sealants
Dubai-based Tremco (Middle East) Limited provides an insight into the key factors that must be taken into account when determining the most suitable sealant for the job.
01 October 2005
The performance of the sealant joints has even more significance in modern buildings than in traditional – a result of the greater design flexibility afforded by the use of new materials and construction techniques.
Joints and joint weatherproofing systems require detailed consideration to minimise the risk of failure, and the parameters for joint design and product selection need to be properly understood.
The behaviour of joints in buildings has been widely studied in recent years and there is now considerable knowledge of the extent and rate of movement of a variety of materials, components and their methods of assembly.
Joint design and sealant selection are, of necessity, very closely interlinked, since the movement in, and dimensions of any joint, will have a major influence on the choice of sealant.
Joints can be broadly classified into two main categories: Those which occur because of discontinuity arising from assembly of individual components – for example, a window frame into surrounding structure and those which are designed specifically to accommodate structural movement. For the purpose of specifying a sealant system, the principal considerations are identical.
Specifying sealants
A number of factors need to be taken into account in determining the most suitable sealant:
• Extent and rate of movement: Movement can occur in a joint for many reasons including thermal cycling, building settlement or wind loading, amongst others. The total amount and type of movement that is expected to occur in a joint will have a major influence on product selection. Where rapid movement occurs – such as in lightweight cladding materials – properties of elasticity in the sealant should be a high priority. In slow moving joints, sealants that exhibit stress relaxation properties may be more appropriate.
• Joint size: Some sealants exhibit better resistance than others to slump and cold flow. Care needs to be exercised to ensure that sealants are only installed into joint widths within their specified slump limits. This means attention needs to be paid to the joint design where width-to-depth ratios play a major part, again reference to manufacturers technical data will be needed.
• Priming: In certain cases, primers may be required to ensure positive adhesion of a sealant to the adjoining substrate. It is vital that the correct primer is specified and used at the correct coverage. Special or uncommon substrates should undergo a laboratory trial to prove adhesion and confirm primer type.
• Substrate preparation: Care should be taken to ensure that joint substrates are prepared properly and such preparation procedures stated within the specification. Substrates should be prepared in accordance with the sealant manufacturer’s recommendations, otherwise premature joint failure may occur. Over 90 per cent of all joint failures result from poor or inadequate preparation.
Joints where one or both faces have a weak or friable surface should be avoided, but where this is not possible, sealants with a low modulus of elasticity are preferred. Sealants with a high degree of elastic recovery will impose continuous stress on the interface and are best avoided in this situation.
• Conditions in service: The environmental conditions to which a sealant is subjected will also affect its performance. Consequently, this factor must influence initial sealant selection. For example, temperature changes in building components forming the joint are often far greater than the ambient ones. This is especially true of dark-coloured materials, which absorb radiated heat. These high temperature changes cause greater joint movement and demand extra performance from the sealant to meet both the annual and diurnal cycles. Other situations demand different properties in a sealant.
Exposure to high humidity, chemical spillage, mechanical damage, permanent submersion, high UV (ultraviolet) radiation, traffic use, bio-degradation, colour stability are a few examples contributing to the complexity of choice.
• Economics: It is important to choose the sealant that exhibits the most appropriate properties for the job – which may not necessarily be the most expensive nor the one with the highest performance properties. The key properties that are needed to allow the joint to perform long term – which may be movement, chemical resistance, aesthetics or a combination of factors – should be determined and the sealant with those key properties should be specified. Joint costs of material and labour vary dramatically – the material component usually by wastage and cross-sectional area, and the labour component by the effort per linear metre.
The manufacturer’s recommended maximum depth and pot life should be checked, together with the contractor’s installation procedures. These last two points alone will make a valuable contribution to keeping the joint design competitive and the project maintenance free.
Leading supplier
The continued trend in the region towards development of modern buildings with sophisticated curtain-walls and high-performance glazing projects. Tremco Limited - as a supplier of high-performance sealants, gaskets and tapes to all the major aluminium and glass companies – has developed a major presence throughout the Middle East.
Tremco’s sealants, tapes and gaskets have been utilised on several of the largest projects in the Middle East – namely the Kingdom Trade Centre in Saudi Arabia and Emirates Towers, Dubai Airport expansion and the Burj Al Arab Tower projects, all in Dubai.
Although most glazing work requires the use of high-performance silicone sealants, Tremco is also able to offer a vast range of other sealants, including polyurethanes, butyls, acrylics and thermoplastics. This means that the contractors can rely on one source of supply for all the ancillary sealant requirements while ensuring the all-important chemical compatibility of the various sealants used in any particular project.
Technical support
A significant benefit to customers and consultants in the industry is Tremco’s technical and practical support, which is available locally via engineers resident in the region, providing immediate access to the resources and experience accrued by Tremco over its 70 years in the sealant and waterproofing industries.
This level of service and support remains unmatched by competitors and is a large part of Tremco’s strong relationships with customers throughout the region.
