Dowsil Sealant Selected for Refurbishment of Iconic Office Building

Multiseal Services Ltd., a contractor specialising in the application of silicone sealants and mastics, recently utilised Dowsil’s 791T low modulus weatherproof sealant during the demanding refurbishment of an iconic office building in Ipswich. The Dowsil product was selected due to Multiseal’s previous experience working with Dowsil High Performance Building solutions and its good working relationship with The Sherwin Williams Company, which manufactures and distributes Dowsil products in the UK.

Originally completed in 1975, The Willis Building was designed by the internationally renowned architect, Sir Norman Foster, and is considered to be the forerunner for High Tech office design.  Still occupied by the insurance company now known as Willis Towers Watson, the structure is currently undergoing a programme of renovations and improvements led by contractor Novum Structures; while Multiseal is carrying out the glazing repairs and replacing all of the old joint seals.

Novum was first awarded the contract for the maintenance of the glazing for The Wills Building in May 2019. This involved a complete re-seal of all the mastic to the glass joint. Following these works Novum then became responsible for replacing broken units caused by a number of factors, from stones thrown up by passing traffic to bird strikes.

The Managing Director of Multiseal, Damian Corner, commented: “We have been carrying out work with Novum for more than a decade, on a number of new and maintenance projects. The famous Willis Building in Ipswich came about because of Novum’s continued and growing reputation within the glass industry. The glazing is old – though a number of the plate glass panels have been replaced due to breakages – and the high-modulus mastic previously used was generally in a poor condition. We were asked to carry out a preliminary survey on the glazing, and there were a lot of places where you could just pull the mastic out of the joints.

“I have been using Dowsil sealants since my father brought me into the business, and have a very good working relationship with The Sherwin Williams Company, which manufactures and distributes Dowsil High Performance Construction products in the UK, and its local Area Manager, Clive Ely.  He came in and looked at the glazing with us after the survey, confirming my decision to use the Dowsil 791T Weatherproofing Silicone Sealant – it is a premium product which you can always rely on for high performance in demanding conditions. Clive then returned following the initial phase to conduct pull tests and pressure tests, which confirmed the adhesion to the films, which had previously been applied to the glass inside and out.”

Since the start of the work early last year, a full five pallets of the product have been used by Multiseal, along with ancillary Dowsil products.  Despite the dark tinted glass giving the building its distinctive appearance, the translucent (T) version of Dowsil 791 was selected to respect the transparency of the view from within the occupied space.

Damian went on to explain: “By using the clear version of the Dowsil 791 you just get a free-floating appearance against the structural fins, as the glazing appears clear from inside the offices or the roof top canteen, which was the last area we addressed. Then in addition to the 791T, we also made use of Dowsil R40 cleaner to remove any residue on the surfaces; it has been a very successful project despite the interruption caused by the coronavirus lockdown.”

Novum is an international specialist contractor well known for the design, manufacture and supply of innovative architectural structures as well as their enclosures.  The company also undertakes facilities management across both the UK and Europe.

Dowsil 791 is a premium quality low modulus, weatherproof silicone sealant developed for glass-to-glass assemblies, which gives excellent adhesion to both porous and non-porous construction materials.  It does not require the use of a primer and it can also be used for frame sealing and joints.  The sealant can be utilised in temperatures from -20o to +50o C and is tack free in just two hours.  Dowsil 791 is available in a range of nine colours, remaining resistant to UV radiation, ozone and extreme weather conditions.

For more information on the Dowsil High Performance Construction Sealant range, please visit