Professor Tanaka discusses areas of research in joint sealing materials

Kyoji Tanaka, professor emeritus at Tokyo Institute of Technology, taught materials science for 40 years, mainly focusing on sealing materials and sealing technology. He chaired a working group on the development of Japanese industry standards for sealing materials and is overseeing the group’s revision of these standards this year in the same capacity.

Why is the durability of sealants and adhesives so hugely important in buildings?

Prof. Tanaka: There are several reasons. Unless high-grade sealants and adhesives are used, it is no longer possible to satisfy the increasingly stringent technical, commercial and ecological requirements that are placed on buildings. As a consequence, the main challenge today is to adapt their durability to the service life of the building as a whole. Subsequent secondary sealing work is difficult and, particularly with high-rise buildings, involves a significant investment of time and money. This alone makes the durability of sealants and adhesives a key economic factor for building contractors and property owners.

Another reason is the reduction in environmental pollution. Although joint sealing materials are produced with relatively little raw material and energy compared with other building materials (e.g. concrete or glass), they make a disproportionately high contribution to improving a building’s overall energy balance. The more durable the sealants and adhesives, the less frequently they have to be renewed and the lower the material consumptions. Durability reduces maintenance costs and improves the carbon footprint at the same time.

What are the key areas of research?

The critical point is always the joint between the sealing material and the construction component. The priority, therefore, is to develop sealants and primers with good adhesive properties on a variety of surfaces.

Another area is single-component technology. Many Japanese architects and engineers still believe that two-component sealants are superior to single-component sealants as regards joint expansion capability and weather resistance, but they are gradually beginning to rethink their attitude. The single-component products can be used immediately, require less specialized knowledge and are much easier to handle. This is an important quality criterion not least because the construction industry is employing fewer and fewer fully trained experts.

What is driving this development?

The demand for energy efficiency, cost pressures, technological progress as regards building materials and the life-cycle approach. For some time now, the climate footprint of buildings has been not just an ecological but, above all, an economic management tool.

What are the most important measures in this context?

Enhancing durability, improving long-term adhesion on a variety of surfaces and faster procedures for testing long-term properties. These are “accelerated aging” test procedures which deliver reliable results, not after years but within weeks. This is particularly important because new innovative building materials and building technologies are constantly coming onto the market and sealants and adhesives need to take account of them.

You live in Japan, where the buildings are regularly subjected to earthquakes and typhoons. What role do sealants and adhesives play under such extreme conditions?

The joints between building components are exposed to huge forces. This applies especially to rain-screen cladding. Consequently, the joint sealing materials need to withstand varying movements for the longest-possible time while suffering the least-possible damage.

Earthquakes cause short-term but intense movements. Heat and cold, day and night cause constant alternation between slow expansion and contraction. During typhoons, the joint seals also have to be able to withstand extreme external influences such as storm-force winds and heavy rain. Optimum adhesion, flexibility, tear and weather resistance over a long time are the main criteria which the sealants and adhesives need to satisfy.

But there is something else as well: the design of the joint also has a role to play. Architects prefer narrow, inconspicuous joints and this requires sealants with special mechanical properties, i.e. preferably those with a particularly high movement absorption capability, such as +100/-50%.

When investigating joint seals after the Hanshinn-awaji earthquake in 1995, we repeatedly found that although the adhesive seals had been partly destroyed, they were still able to retain their hold on smaller parts of buildings, such as glass roof panels or ceramic tiles, and prevent them from falling. This revealed a hitherto hidden characteristic of sealants and adhesives: they have a safety function and act as a sort of back up.

You were involved in developing industry standards for tall buildings. How much did your investigations contribute to the new standards for sealants and adhesives?

The results of my investigations into the weather resistance of synthetic polymer-based materials have been incorporated into a number of standards for the test methods for classifying durability. My investigations into the long-term behavior of sealants in moving joints also acted as the basis for discussion about test methods and was of some help in devising Japanese industry standard JIS A 5758 for building seals and glazing.

Thank you for taking the time to talk to us.