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Concrete

• Visual concrete
• Reference sources

Visual concrete

Visual concrete generally

It is important to appreciate that an acceptable appearance for visual concrete cannot be achieved through a written specification alone. It should be established as early as possible that the required finishes are achievable within the cost constraints and then a written specification can be discussed and adapted if necessary so that it is achievable and affordable. Clear communication is required between members of this team so that the results do not fall short of expectations.

This sobering comment, quoted verbatim, is extracted from an excellent brief commentary on specifying visual concrete included in Concrete Structures 10, published by the Concrete Centre in September 2010. The full article is available from this link.

• How to specify in-situ visual concrete - CS10 pages 10 to 12

National Structural Concrete Specification

The specification of visual concrete has been a topical issue since the publication of the 4th Edition of the National Structural Concrete Specification in April 2010. The previous specifications found in BS 8110 have been replaced by four different classes of formed finish: basic, ordinary, plain and special. The relevant clauses are in Section 8.6 of the NSCS Standard Specification and in Section P 1.9 of the NSCS Project Specification. The Guidance notes are in Section 8.6 of the NSCS Guidance. These three documents are contained in the single PDF download of the National Structural Concrete Specification (see Reference sources - Construct below).

Reference panels showing acceptable examples of the Ordinary and Plain finishes have been constructed at six locations across the UK - see [www.construct.org.uk] - and these can be referred to in the project specification. The reference panels do not replace project-specific control samples for Plain finishes - see NSCS Guidance 8.6.1.3.

	NSCS Standard	NSCS Project	NSCS Guidance	Reference Panels	Sample Panels	NBS 2010-1	Notes
Basic	8.6.2.1	-	8.6.1.1	No	N/A	(E20/610)	NBS to be updated in 2010-3.
Ordinary	8.6.2.2	P1.9.1	8.6.1.2	Yes	N/A	(E20/635)	NBS to be updated in 2010-3.
Plain	8.6.2.3	P1.9.1	8.6.1.3	Yes	Desirable	(E20/620)	NBS to be updated in 2010-3.
Special	8.6.2.4	P1.9.2	8.6.1.4	No	Essential	(E20/630)	NBS to be updated in 2010-3.

Key points

• An Ordinary finish is the default formed finish unless specified otherwise.
• Only Plain and Special finishes can be considered as "visual concrete".
• A Plain finish is generally acceptable in areas where appearance is not important, and may be acceptable in areas to be painted.
• A Special finish should always be specified as the basis for a worked finish (such as sand-blasting or bush-hammering) or where the formwork is not a standard sheet material (such as where rough boarded or ribbed finishes are required).
• A Special finish should always be specified where colour is important (such as for white concrete).
• A Special finish will always require a project-specific specification covering, as a minimum, the criteria listed in NSCS Guidance 8.6.1.4.
• A Special finish may justify the construction of a sample panel before the project is tendered or before the cost of the formed concrete is agreed.
• A Special finish cannot be achieved by a written specification alone - see quotation at top of page.

White concrete

White concrete is notoriously difficult to specify and achieve - see the notes on Colour in NSCS Guidance 8.6.1.4. Extensive research, and project-specific samples, at the earliest possible stage are essential. Specifying white cement is only the most basic starting point, selecting appropriate sands and aggregates are essential. The extract from Concrete Quarterly, and the website of Aalborg Portland, provide basic information to get you started.

• Getting it white - and counting the cost - CQ188 - page 14
• Publications from Aalborg Portland

Specifiers should be aware that some well-known buildings, which you may believe to be high-quality white concrete, are actually finished with one of the specialist paints, such as Keim Concretal Lasur, formulated specifically to retain the appearance of a natural concrete finish whilst improving the colour consistency.

Reference sources

Architectural Cladding Association

• www.architectural-cladding-association.org.uk
• "The Architectural Cladding Association's principal objectives are to increase awareness of architectural precast cladding and provide technical advice to specifiers and users. Members of the Association are required to meet strict criteria including a proven track record in design, manufacture and site erection."
• The ACA is the trade organisation for the UK precast cladding industry. There are currently (November 2010) just three members: Decomo, The Marble Mosaic Company, and Techcrete. With Decomo based in Belgium, and Techcrete based in Ireland (although with a UK manufacturing facility and design office), that leaves Marble Mosaic as the only truly UK-based manufacturer of precast concrete cladding.

The Concrete Centre

• www.concretecentre.com
• www.thisisconcrete.co.uk
• "The Concrete Centre is the central development organisation for the UK concrete industry with the aim to enable all those involved in the design, use and performance of concrete to realise the full potential of concrete and make it the material of choice, by providing a connection between producers and manufacturers, designers and engineers, contractors and clients."
• The Concrete Centre publishes a large amount of technical material. Some publications are available as free downloads from the Online Services page.
• The Concrete Centre publishes the well-respected Concrete Quarterly magazine. The complete archive, going right back to Number One (July 1947), is available online from the Concrete Quarterly page.

The Concrete Society

• www.concrete.org.uk
• "The activities of The Society's advisory, technical development, professional/business networking, CPD and information services provide the construction industry with a major focal point for information and a proactive forum for debate and action. We play a vital role in encouraging the use and development of concrete as a uniquely versatile and competitive material."
• The Concrete Society provides products and services available to members only.

Construct (Concrete structures group)

• www.construct.org.uk
• "CONSTRUCT is an association of member companies dedicated to the task of improving the efficiency of building in-situ concrete frames and associated structures."
• Construct publishes the National Structural Concrete Specification available as a free PDF download from the Publications page of the Construct website.

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