Contractor Balfour Beatty has made substantial savings on a £6.4m Child Development Centre in Hackney, East London by using the Celcon Thin-Joint System from H+H UK.
The project comprised two L-shaped buildings in a ‘69’ layout with a central courtyard. One building is two stories high with glass curtain walling, the other is four stories with solid, Thin-Jointed aircrete walls using Celcon Plus blocks 200mm thick. The two buildings take up the whole of the site.
The original specification for the four-storey building was dense block externally with a render finish. Internal lining was to have been a Metsec frame system with a dry-lined, plasterboard finish. However, while the Metsec frame is quick to erect, lead times are lengthy and overall construction time would have been slow, due to the time required to build the dense block wall for the outer leaf. Balfour Beatty project manager Steve Penwill had used Celcon blocks with Thin-Joint technology on an extension to his home and had been pleased with the results, so he decided to look at the system for this project.
A solid aircrete wall solution negated the need for the Metsec frame and Thin-Joint technology, using quick-setting Celfix mortar, ensured that the wall was built in a much quicker time than a dense aggregate wall with conventional mortar would have been. Masonry blockwork was also more flexible in use than the Metsec frame system. The solid wall was finished with insulated render on the exterior and dry-lined on the inside.
This was the first major project that Balfour Beatty had used the Thin-Joint System on. H+H helped with the development of the design, advised on acoustic solutions and produced U-value calculations. An excellent U-value of 0.30 W/m²K was achieved. Detailed advice was given on the use of bed joint reinforcement which both reduced the amount of reinforcement needed and enabled the number of windposts to be reduced, resulting in a significant reduction in costs. H+H also provided advice on waste minimisation and the recycling of aircrete block off cuts.
Project manager Steve Penwill commented: “It’s a very good system and we will certainly be using it again. Overall, we reckon that aircrete blockwork saved us something between £60,000 and £80,000 compared to a Metsec frame system and including the savings from fewer wind posts and bed reinforcement joints. The reduced amount of waste using aircrete and being able to recycle it is also a major benefit, especially for public sector projects.”
By accepting that buildings settle and move and concrete constructions such as blockwork can create their own movement joints which are not critical structurally, the engineers’ design of the blockwork allowed any movement to be hidden behind internal and external finishes. This also enabled the structural engineers to ‘value engineer’ the wall – to save costs without compromising performance.
Bed joint reinforcement was used in certain areas, such as above and below windows. Despite the expense of this reinforcement, if used correctly, it reduces the need for windposts and so cuts costs significantly. The use of an insulated render also allowed the structural engineers to design out a significant number of wind posts that would otherwise have been necessary to provide lateral support
The Celcon Thin-Joint System enabled the building to be built faster and to a better quality, allowing follow-on trades to start work sooner in a weatherproof environment, while retaining the flexibility of on-site construction.