Introduction
Ceramic tiles have been used for wall decoration and cladding since Ancient Egyptian times. Current trends are for terracotta rainscreen cladding and brick slip systems, as well as the more traditional applied tiles and vertical clay tile hangings.
Ceramic rainscreen cladding
Terracotta and ceramic tiles are common rainscreen cladding options. For certainty of performance, specify systems meeting the Standard for systemised building envelopes produced by the Centre for Window and Cladding Technology. Systems produced to Continental standards should be verified for their applicability to specific UK conditions.
The performance of the cladding units is related to exposure rather than weathertightness as rainscreen cladding is designed to accommodate some moisture penetration. To prevent moisture penetration to the inner leaf, it is critical that the detailing around openings and fire barriers to maintains drainage, ventilation and integrity of the system. This may be achieved with purpose-made profiles and dampproof trays.
Support structures typically comprise aluminium brackets and bearers with non–corrosive fixings, specialist adhesives or clips. The deflection tolerances of the building and cladding system should be compatible.
Damaged tiles may be costly to replace where extensive sections of the cladding have to be removed to gain access. Impact damage is a common at pedestrian levels. This is covered by a code of practice for the surface repair and cleaning of buildings: BS 8221 parts 1 and 2.
Brick slips
There are no specific standards for brick slips. Third party certification provides performance confirmation of the system as a whole. This includes backing (mortar, grout or adhesive), resistance to wind-driven rain, wind pressure, cyclic freeze-thaw, hard body impact and fire.
Where brick slips are attached to foam insulation, special precautions may be required to limit spread of fire. BRE’s report on fire performance of external thermal insulation for walls of multistorey buildings gives generic guidance on assessing external fire performance.
Applied ceramic tiles
The long-term performance of applied ceramic tiles relies on correct component selection, design and installation. Replacing detached tiles is often expensive.
Ceramic tiles should be to BS EN 14411 for confirmation of properties such as frost resistance and crazing resistance:
• Up to first-floor level, use extruded or pressed ceramic tiles of group AI, BIa or BIb, with water absorption of less than 3%.
• Above first-floor height use Group BIa dry pressed ceramic tiles water absorption of less than 0.5%.
Adhesives should be to BS EN 12004. Ceramic tiles larger than 300 x 300mm (0.1m2) should be mechanically fixed. The background must be capable of supporting and receiving the tiling system. Joint sealant selection and application must meet BS 6213. Grouts must meet BS EN 13888 for modified cement or epoxide resin mixes. Metal reinforcement and fixings, if used, should be austenitic stainless steel.
BS 5385 is the code of practice for the design and installation of external ceramic and mosaic wall tiling. Adhesive bedding is the preferred method of applying tiles. Sand and cement mortar bedding is limited to mosaics and tiles with a back designed to lock to the mortar.
Further guidance on installation is offered by BS 8000–11.1, which should be considered in conjunction with the maker’s recommendations.
Vertical clay tile hanging
Clay tiles to BS EN 1304 give assurance of performance, particularly frost resistance and impermeability. BS 5534 is the code of practice for design and installation. As with other forms of cladding the complete system must be designed for a given location and environment including pull-out resistance, especially at corners; junctions with dissimilar materials, flashings; use of corrosion resistant fixings; support battens and underlay.
Specification options
| Ceramic external wall claddings | Capital cost £/m² |
Net present value for 60 years£/m² |
| Terracotta rainscreen cladding to CWCT standard on aluminium support system | 230 - 280 | 300 |
| Brick slip system on insulant backing with third party approval | 120 - 140 | 160 |
| Brick slip system on galvanized steel backing with third party approval | 150 - 180 | 200 |
| Ceramic tiles to BS EN 14411Group BIa fixed with adhesive | 160 - 200 | 220 |
| Vertically hung plain clay tiles to BS EN 1304. Flexural strength 600N minimum. Frost resistance: pass frost test D to BS EN 539–2; 265 x 165mm | 100 - 120 | 130 |
Table notes
• Design service lives for all components is 60 years, in practice service lives greatly in excess of this are achievable; shorter lives have been the result of not following good practice guidance in design and installation.
• Capital costs are based on the average and include the cladding; breather membrane and support system if required. A nominal allowance for detailing, junctions and movement joints is included. Insulation and wall structure are excluded.
• In use costs include nominal amounts for cleaning, re-pointing or regrouting where applicable and minor repairs.
• A discount rate of 3.5% is used to calculate net present values.
• A cost analysis based on project specific information is essential for a realistic best value appraisal.
First published in Building 2007
Further information
BLP provides latent defect warranties for buildings www.blpinsurance.com
Further information contact peter.mayer@blpinsurance.com or telephone: 020 7204 2450.