Glass blocks

Glass blocks for non-load-bearing walls and partitions are manufactured by casting two half blocks at 1050°C, joining them together at 800°C, followed by annealing at 560°C. The void space is partially evacuated, giving a U-value of 2.5 W/m2 K. The standard blocks (Fig. 7.4) are 115,190, 240 and 300 mm square with thicknesses of 80 and 100 mm, although rectangular and circular blocks are also available. Walls may be curved as illustrated in Figure 7.5. The variety of patterns offering differing degrees of privacy, include clear, frosted, Flemish, reeded, and crystal designs with colours from blue, green and grey to pink and gold. Blocks with solar reflective glass or incorporating white glass fibres offer additional solar control; colour may be added either to the edge coating or the glass itself. Special blocks are also available to form corners and ends, also for ventilation.

For exterior and fire-retarding applications natural or coloured mortar (2 parts Portland cement, 1 part lime, 8 parts sand) is used for the jointing. Walls may be straight or curved; in the latter case, the minimum radius varies according to the block size and manufacturer's specification. Vandal- and bullet-proof blocks are available for situations requiring higher security. For interior use, blocks may be laid with sealant rather than mortar. Glass blocks are now available in preformed panels for speedier installation.

Glass blocks jointed with mortar give a fire resistance of 30 or 60 minutes with respect to stability and integrity but not insulation, according to the BS 476: Part 22: 1987 or BS EN 1364-1: 1999. Fire stop blocks (F-30) manufactured from 26 mm rather than 8 mm glass offer the increased fire protection of two hours' integrity and 30 minutes' thermal insulation. Sound reduction over the 100-3150 Hz range is typically 40-2 dB for standard blocks, but up to 45-9 dB for the

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Fig. 7.5 Glass Blocks. Photograph: Courtesy of Glass Block Technology-(www.glassblocks.co.uk)

F-30 blocks. Visible light transmission ranges downwards from 85 to 77% depending upon the pattern and block size, but this is reduced to 60% for coloured glass.

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