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Glass blocks look for support

A revival of interest in glass blocks is being hampered by the lack of an agreed standard and clear technical information

Equated with '60s and '70s kitsch, glass blocks became relatively marginal to the construction industry due to changing fashions. In the past few years they have made a strong comeback, with high-profile use on Terry Farrell's Centre for Life in Newcastle upon Tyne among others.However, there is no UK industry standard nor regulatory guidance on the manufacture, supply and installation of the system, and getting relevant fixing and construction details is often incredibly tiresome.

The historical development of different national practices has mitigated against an agreed international standard and the British market is predominantly served by European manufacturers reliant on DIN 18175 for their manufactured quality. Existing literature - commonly translated from the French - tends to be directed towards the contractor, rather than the designer. DIN standards do not cover installation or workmanship and therefore the UK is reliant on tested, best practice and - to a certain extent - rule of thumb.

Roger Barnes of Glass Block Technology confirms that all technical information about glass blocks is based on tested methodology and calculation. The lack of accessible information means that he spends much of his time dealing with installation queries on the phone and on site. The most frequently asked questions concern relatively straightforward construction details.

It is recommended that glass block walls are installed into prepared openings - as they tend to be self-supporting rather than loadbearing - although this means that there should be restraint to jambs and head. Specifiers should be aware that the opening sizes should be premised on the need for 190 x 190 x 80mm thick grid.

Glass blocks cannot be cut to fit an opening that is too small, but additional grouting can feasibly take up space if the opening is oversized. Therefore, to calculate the opening size one should use the same principle that one would use to calculate brick opening sizes - allow for a 200mm grid plus 10mm.

Reinforcement bars are set into the jambs (grouted into pre-drilled holes in masonry, for example), set out to suit the grid size of the glass blocks. Rebates are recommended to aid lateral restraint. Set the first row of glass blocks on a bedding layer of mortar reinforced with one, two or three steel bars. Place the vertical steel bars at grid centres and dry grout between glass blocks. Repeat the process, using single reinforcement at every horizontal joint. On completion, the joints should be sealed with polysulphide pointing or struck off as required. It tends to be as simple as that, although the size, placement and tying in details of the reinforcement, edge restraint and mortar strength information is where the expertise is needed.

Free-standing walls can be created provided some end of wall restraint is used. It is normally recommended that steel channels (or angles, depending on the likely direction of applied force) be fixed to capture the sides of the glass walling. In this scenario, the horizontal reinforcing bars should be secured to the vertical channels to ensure rigidity.Head fixings for low-level walls are also recommended, although until technical literature is available expert opinion should be sought on each case.

Glass block features are designated as waterproof, depending on the pointing characteristics. Indeed, glass blocks recently appeared on a 'designer gardening' programme as the ubiquitous 'water feature'with water flowing over the face.

The European Centre Scientifique des technique du batiment (CSTB) has certified the standard construction to be one hour fire resistant using 100mm thick blocks.However, further details should be sought about the exact method of construction because of the differences between the French standard's definition of 'integrity' and 'stability'. In general, though, the CSTB designation and fire certification can be used to satisfy Part B of the Building Regulations Approved Documentation.

It would seem that glass walling has come of age.Used internally or externally, glass blocks create a self-supporting decorative surface which can rise to considerable heights, allowing good light transfer between spaces.

Roger Barnes notes that 'the European market has led the way, but now a new generation of British architects is becoming aware of the possibilities of the materials'.With a range of sizes, strengths and colours available, all we need now are some coherent standards and some rigorous technical information.

For more information contact Roger Barnes on 01746 780026

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