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Frequently Asked Questions

CBA members receive hundreds of calls from specifiers and users of their products. Enquiries are often of a similar nature and the CBA have compiled answers to the most common questions.

The manufacturing Standard is BS EN 771-3 ‘Specification for masonry units. Aggregate concrete masonry units (Dense and lightweight aggregates)’.

Other relevant masonry standards include:-

  1. PD 6697: Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2
  2. BS EN 1996-1-1: Eurocode 6. Design of masonry structures. General rules for reinforced and unreinforced masonry structures

This is to be read with the National Annex: NA to BS EN 1996-1-1: Design of masonry structures. General rules for reinforced and unreinforced masonry structures

  • BS EN 1996-2: Eurocode 6. Design of masonry structures. Design considerations, selection of materials and execution of masonry

This to be read with the National Annex to BS EN 1996-1-2:  Design of masonry structures. General rules. Structural fire design

  1. BS 8103-3: Structural design of low-rise buildings. Code of practice for masonry walls for housing
  2. BS 6073-2: Precast concrete masonry units. Guide for specifying precast concrete masonry units
  3. BS EN 1996-1-2: Eurocode 6. Design of masonry structures. General rules. Structural fire design

This depends on the type and thickness of materials used to construct the wall, including all airspaces. For convenience, a simple U-value calculator is available to use on the CBA Web site and CBA members can provide product specific U-value calculations.

Careful selection of mortar is essential. Guidance is given in a number of publications including PD 6697: Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2 as well as BS EN 998-2 Specification for mortar for masonry. Masonry mortar

The location of the blockwork is an important consideration, and as a guide stronger mortars will be required in high exposure situations. Similarly the design of walls employing high strength blocks, typically 10.4N/mm2 or greater, will result in enhanced loadbearing capacity when mortar strength Class M6 or M12 mortar mixes are used. However, for the construction of most internal walls including the inner leaves of cavity walls above ground, it is common practice to specify mortars no stronger than Class M4 strength e.g. a 1:1:6  cement, lime, sand composition or similar designation (iii) mix.

Aggregate blocks can be used to construct solid and cavity separating walls with plaster or drylined finishes. For solid walls, dense solid blocks are advocated to construct 215mm walls (100mm blocks laid flat). For cavity walls, 100mm thickness lightweight or dense aggregate blocks can be used depending on cavity width and type of surface finish.

There is an extensive number of Robust Detail specifications available that feature both generic and manufacturer specific aggregate blocks. Use of Robust Detail constructions will allow Part E, or in Scotland Section 5, of the Building Regulations to be met without the need to undertake pre-completion testing.

Vertical movement joints should be considered at about 6 to 9 metre intervals, depending on block type, but their inclusion is not normally required in internal walls in dwellings. Special attention should be given to low height panels and areas of high stress concentration. Guidance is given in CBA datasheet – Guide to Movement control or consult CBA member’s literature.

When properly constructed, masonry wall construction requires little maintenance compared to other wall systems.

Aggregate concrete blocks themselves will require no maintenance. The service life of masonry is typically in excess of 100 years. maintenance  issues for walls will normally include replacement of sealant in movement joints and at junctions / openings

The service life of masonry can be 100 years or more. Maintenance issues will normally include the replacement of sealant in movement joints, and at junctions / openings and repointing of external walls.

Most CBA members can provide a close textured/paint grade aggregate block suitable for direct painting. These products are very robust and provide good resistance to impact damage

All types of aggregate block are suitable for use to the inner leaf of external cavity walls, or internal walls below ground. For the external leaf of external cavity walls, or solid external walls, dense or lightweight 7.3N/mm2 blocks or aggregate blocks with a density of at least 1500kg/m3 are all suitable. Where unusual ground conditions exist, or for more information, please contact CBA members for advice or see CBA Datasheet – Use in Sulphate Soil Conditions

A number of products can be used depending on design requirements. These include dense and lightweight aggregate blocks 7.3N/mm2 (solid & cellular), or 3.6N/mm2 blocks which have been transverse load tested. Generally 100mm thickness blocks are used.

This will depend on the length and height of the wall and what restraint is to be provided to the wall. Restraint could be provided to the ends of the wall, to the top of the wall or a combination of both. Limiting wall dimensions can be obtained from BS EN 1996-1-1: Eurocode 6.  Design of masonry structures. General rules for reinforced and unreinforced masonry structures. CBA members can provide simple to use tables of acceptable block panel sizes based on BS EN 1996-1-1 recommendations.