After 18 months of work, the façades of the iconic Torre Velasca, a design by BBPR in Brutalist style dating back to the post-war era, are once again bringing colour to the skyline of Milan with their authentic shimmering colour that changes throughout the day, thanks to this particular render containing Velasca Binder, developed by Mapei Research, and a mix of aggregates in various particle sizes and colours.
Torre Velasca was the object of attentive restoration and redevelopment work, developed by Hines as development manager, which also included the façades, exposed for more than 60 years to pollution and atmospheric agents without ever undergoing any maintenance work. And Mapei was in the front line, along with the Milan Research and Development laboratories and the Technical Services team on site, constantly coordinating with Hines, the Archaeology, Fine Arts and Landscape Authority, Asti Architetti and CEAS design studios and the main contractor ARS Aedificandi.
The restoration work on Torre Velasca is just part of a more extensive redevelopment programme covering not only the exterior of the tower, but also the interior.
Preparation and restoration of concrete surfaces
The first phase of the work included preparation of the surfaces and removal of the damaged, carbonated concrete to leave a rough, compact surface free of dust. After hydro-scarifying the rusty exposed rebar, it was treated with Mapefer 1K anti-corrosion cementitious mortar, which is used to protect reinforcement rods and, in this case, improve adhesion of the Mapegrout 430 mortar used to repair the concrete. This fibre-reinforced, compensated-shrinkage, thixotropic mortar was used to reintegrate the areas where the concrete had been removed and was applied in layers at least 10 mm thick according to the depths indicated by a series of check-dowels mapping out the form and geometry of the original concrete. Mapegrout 430 was chosen because its mechanical characteristics are compatible with those of the substrate, and also thanks to its excellent characteristics of workability and pumpability using both separate and continuous-feed mortar pumps.
Velasca Binder to restore the original shade
After repairing and reintegrating the concrete, Mapei stepped in to return the façades to their original colour. This part of the work required both scientific and materic analyses, a series of laboratory test, identification of the most suitable aggregates, choosing the right particle size and the right colours and the development of a specific, bespoke binder for Torre Velasca, from which it takes its name.
This product is a decorative, white, cement-based formulate with specific polymers so that it can be mixed with the aggregates, which were recreated to match the type and particle size of the original render of that era to create a formula as close as possible to the authentic colour of the render used for the façades of the tower. Velasca Binder, which is made using aggregates from the Bellamoli quarries and Ferrari, is the result of various tests performed both in situ and in the laboratory aimed at complying with the requirements of the Local Heritage Authority, in terms of colour and texture, and to achieve the best results possible from a conservative restoration perspective.
Velasca Binder is formulated using a mixture of light coloured binders, special additives and fine, mineral fillers to create a highly adhesive, water-repellent product with no cracks that guarantees the maximum durability possible for surfaces exposed to aggressive atmospheric agents and the urban environment in general, and also maximum compatibility with the substrate it is applied to while, at the same time, complying with the aesthetic requirements of the project.
In order to ensure the new finishing render adhered firmly, Planitop HDM Maxi fibre-reinforced, highly ductile, Pozzolan-reaction cementitious mortar had to be applied over the whole surface in a layer at least 5 mm thick using a notched trowel.
Water-repellent treatment for the rendered surfaces
The cycle was completed by treating the façades with Planiseal WR 100, a protective waterproofing product which, thanks to its particular composition, penetrates deep down into concrete to prevent degradation phenomenon without affecting its aesthetic characteristics or colour. Thanks to a considerable reduction in their absorbency after being treated with Planiseal WR 100, surfaces are prevented from being damaged by the action of freeze-thaw cycles and, as a result, are much more durable.