Brick/block walling should be specified under Section F10 – Brick/Block Walling, of the CAWS (Common Arrangement for Work Sections) and the CSI Uniclass System for Classification of Work/Trade Sections. Likewise, requirements for insulation and all necessary accessories should be specified under Section F30 – Accessories/Sundry Items for Brick/Block/Stone Walling, as appropriate for the project.
In normal circumstances, where the architect is responsible for the detailed design of the masonry, the specification should be prescriptive – that is, with fully detailed materials and workmanship clauses.
In more bespoke circumstances, where the design dictates that the responsibility for the detailed design lies with the contractor, the specification should state specific performance requirements in respect of:
- Structural movements and deflections
- Specific dead and live loads
- Wind loads (including wind post design)
- Acoustic requirements
- Fire resistance
- Thermal performance requirements.
For each type of brick required, the specification should include clauses on:
- Durability: State grade according to frost resistance and soluble salts content (to BS 3921 and BS 5628)
- Compressive strength: In no case less than 5N/mm2
- Water absorption: Normally only for clay damp-proof course bricks tested to BS EN 772-7
- Size: Working sizes to BS 3921 and as manufacturers' standard range
- Form: Solid, perforated, frogged, hollow or cellular
- Joints: For example flush, struck, bucket handle, recessed, tucked, weather struck and so on
- Bond: Stretcher, English, Flemish, stack and so on
- Special shapes: As required to BS 4729
- Mortar: Specify required mortar mix group in accordance with BS 5628: Part 3, Table 13.
For each type of block required, the specification should include clauses on:
- Form/type: Load bearing/non-load bearing, solid, cellular or hollow in construction
- Compressive strength: Specify minimum compressive strength dependent upon project loading requirements
- Durability: Concrete blocks are not normally suitable for use below ground level, but should be specified with all necessary damp-proof protection in accordance with BS 5628: Part 3, Table 13
- Size: Nominal face dimensions of blocks should be specified and appropriate thickness stated, particularly to meet acoustic and fire rating requirements
- Density: Specify minimum density in kg/m³. (Note: Concrete blocks in excess of 1550 kg/m³ may not meet the CDM weight requirements; they should not exceed 20 kg (44 lb) for a single person handling. Where a heavier block is essential, a risk assessment should be undertaken to comply with the CDM regulations)
- Drying shrinkage: Specify maximum percentage
- Special shapes: For bond beams, lintels, corners and so on
- Finish: Specify fair-faced finish as required
- Bond: Stretcher, stack and so on
- Joints: Flush, bucket handle, recessed, and so on
- Mortar: In accordance with BS 5628: Part 3, Table 13.
- Section F30 of the specification should specify the requirements for insulation within masonry construction, including full fill cavity insulation using mineral fibre batts and partial fill cavity insulation using expanded or foamed plastic boards or mineral fibre slabs.
- The design and construction of the masonry insulation should be specified to lessen the risk of defects through damp penetration and interstitial condensation and to comply with Part 2 of the Building Regulations.
- Installation: Specify installation requirements to meet the relevant category of BS 5628: Part 1
- Tolerances: Specify tolerances, as a minimum to meet BS 8000: Part 3, or better, as required by specific project
- Samples, benchmarks, testing and so on: Specify requirements for samples of bricks, blocks and insulation as required, including all insulation and accessories, of a minimum size 1800 mm x 1800 mm, and to include all interfacing junctions with concrete/steel columns or slabs or adjacent elements of importance. Ensure that test certificates or appropriate literature is provided for all materials, including bricks, blocks, mortar and insulation before commencement of the works on site.