This two layer construction is considered later in this section. The photographs above show an exposed aggregate concrete that has been constructed using the surface dressing method, with a rounded 'golden' gravel, which is popular in SE Britain. Further details on this project are available on request . FAQ - Is a concrete base better than a sub-base beneath block paving? Selected pebbles and larger flattish cobbles set into a reddy-brown mortar matrix were used to create the look of a dry river bed in the outback of Australia in a garden exhibited at the RHS Chelsea Flower Show in 2011 . This process is where exposed aggregate gets its … As a finish they can appear utilitarian or luxurious depending very much upon the chosen materials and installation techniques. Drainage-Channel - Drainage - Linear Drains, Drainage - Manholes and Inspection Chambers, Drainage - Foul or Storm? Only the top layer of stones is exposed, whereas, others remain embedded in the concrete. Also, great care is needed to ensure that the amount of deco-agg that is removed is kept to a minimum, and only the matrix is washed off. Construction follows the principles described on the Concrete Hardstanding page, in that a sub-base is prepared, a damp proof membrane laid and the concrete placed. “Wearing screeds” (formerly known as “high strength concrete toppings”) are usually installed once the space is enclosed, unlike a structural floor slab. Appropriate specification of the concrete mix is essential for a high-quality exposed aggregate finish, since “normal” concrete is unlikely to contain sufficient aggregate at the surface once compacted. The slab is then covered with a temporary damp proof membrane to maintain humidity and left overnight or for a period of 12-18 hours. Exposed concrete floors are suitable for various applications is used for warehouses, galleries etc. Use 2x4s in order to obtain 4 inch thick concrete. Surface retardants offer a more controlled method of exposing the aggregate. The degree to which the deco-agg is forced into the concrete depends on the expertise of the operative, the size of the aggregate itself, the condition of the concrete, the desired finish and the planned use. The material that is washed off contains cement powders, and so should be disposed of carefully. The most common method is installing a pre mixed aggregate concrete. The concrete was first developed and tested to allow us to see how the aggregate behaved during mixing, during transit to the site and during placement. It will eventually set, so should not be allowed to settle onto other paving, which would result in permanent staining, nor should it be left to ssettle on bare earth, but should be collected up and disposed of properly. The depth of mortar removed, and therefore amount of aggregate revealed, is determined by the choice of retardant. This prevents the mix water being drained from the fresh concrete and helps ensure even curing of the slab. Our Privacy Policy / Use of this website and its content implies acceptance and agreement to abide by the Terms & Conditions All information, specification and drawings used on this site are intended for guidance only. The Concrete Centre provides material, design and construction guidance. There are many fine examples of patterns created using stencils with this technique. The top millimetres of the concrete are mechanically ground away to expose the aggregate, often using diamond grinders. The cost can be further controlled by limiting the use of the decorative aggregate, which is commonly the most expensive constituent of the concrete… Shot or grit blasting s a simple technique for mechanically removing the top layer of hard concrete to create a stippled surface, often used to improve adhesion for supplementary finishing layers. This is most commonly achieved using power tools but it is also feasible to trowel small spaces by hand. The Retarder penetrates the top 3-6mm of the concrete and prevents the cement content setting, therefore it is essential that the application of the retarding liquid is even, otherwise the penetration will vary, resulting in a variable surface finish. A water hose with good pressure is the preferred method for washing exposed aggregate. The concrete, which is typically a C20-C35 mix depending on planned use, is tamped to a level approximately 4-9mm below finished paving level. Make sure before you use any chemical driveway cleaning solution that you carefully read the instructions and safety warnings. It is essential to remove all unset matrix, to fully expose the deco-aggregate. The general rule of thumb is to remove the surface mortar to a depth no more than one-third the diameter of the aggregate particle. It can take on the appearance of terrazzo depending upon the colour of cement, pigments and type of aggregates used – specialist suppliers and installers offer a huge range of colours and aggregate combinations. Exposed aggregate also is a great alternative for homeowners who want a decorative finish at an economical cost. Guidelines for Exposed Aggregate Finishes. The next morning, wash off anything that will wash off. Hereafter the aggregate is incorporated into concrete surface through a coarse-mesh. A highly decorative and aesthetically appealling finish with limitless possibilities. Use 2x6s in order to obtain 6 inch thick concrete. Once the freshly-placed concrete has been tamped, the decorative aggregate is introduced and spread evenly over the entire surface. Many include a surface hardener to improve the durability of the floor finish, but they can also provide abrasion resistance and are often used to improve the surface finish of large pours when steel fibres are included. 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