Flooring Solution Exposed Concrete Floors
One of the fastest-growing segments of the flooring industry is concrete floors and recently the hottest flooring trends are exposed to concrete floors. While concrete has been around since the time of the Romans, it has traditionally been used as a core building material, an unfinished floor, or as a substrate for another flooring system.
Not only do they embody the industrial look and are highly appealing, exposed concrete floors are durable, hard-wearing, and ideal for many applications - including warehouses, retail spaces, restaurants, breweries, art galleries, garages, and so much more. They are particularly useful for heavy loads or traffic.
Generally, the upper face of the exposed floor is flat and unformed, unlike other faces which are formed due to formworks. So, the upper face needs to be formed using proper techniques to achieve the required texture and shape. Frequently, polished finishes are considered for exposed concrete floors. A requirement for greater slip resistance is often a driver to explore other options, such as the inclusion of retardants or shot-blasting. Some of the techniques more commonly used for external surfaces, such as imprinting or brushing, can also be used to good aesthetic effect inside.
Polished Concrete Floors
There are two ways to create a smooth, polished patina to concrete floors, but each achieves quite a different visual appearance.
Diamond Ground and Polished Concrete
Polished concrete floors are installed by grinding a concrete slab multiple times with progressively finer diamond grinding tools. The first several steps are called ‘cutting’ and utilize aggressive grinding tools to remove imperfections, flatten and homogenize the surface of the floor. The number of cutting steps is a function of the desired finish and the quality of the concrete mix and pour. It's during this stage that stone aggregate in the concrete can be exposed. The final ‘polishing’ steps utilize less aggressive diamond tools and progressively increase the reflectivity of the concrete surface. The number of polishing steps is dependent on the desired level of reflectivity.
Power Floated and Trowelled Finish
Power floated method is carried prior to the full curing and hardening of concrete, so the success of power floated technique is considerably dependent on the time at which the process is started. Initially, the pan floater is applied to cut the surface of the partially cured concrete and then trowelling is used to smoothen the surface. Commonly, suitable powered tools are used to achieve a designated floor finish, but the application of hand trowelling is also acceptable at small spaces. If it is necessary, a higher degree of polishing can be achieved using various sealants. The colour of the polished surface is governed by fine components of concrete mixture such as cement, sand and pigments if present.
Texture and Pattern
Exposing the aggregate in concrete can also create grain, texture and pattern in floor surfaces, which is particularly useful for areas requiring greater slip resistance, especially when wet. The uppermost layer of concrete, or surface mortar, can be removed in a number of ways, each with subtly different results.
A key consideration is the practicality of application and the degree of control required for the specific project. 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. A range of proprietary mixes is available with different combinations of coloured aggregates and binder. Common techniques include: exposure by washing or brushing, the use of surface retardants or abrasive or shot blasting.
Exposure by Washing or Brushing
This is the oldest method and the simplest because it doesn't require chemical retarders or special tools. It needs to just wash away the thin layer of surface mortar covering the aggregate by spraying with water and scrubbing with a broom until the aggregate is exposed to the desired depth. The timing of the operation is critical, however, so this method is often better suited for small jobs. The work should begin as soon as the surface mortar can be removed without overexposing or dislodging the aggregate.
Use of Surface Retardants
Surface retardants offer a more controlled method of exposing the aggregate. Liquid surface retardant is sprayed onto the surface of the wet concrete, preventing the uppermost layer (known as mortar) from setting and allowing it to be washed or brushed away. The depth of mortar removed, and therefore the amount of aggregate revealed is determined by the choice of retardant.
Texture patterns can be created in the floor surface by using stencils to mask areas of the concrete before the retardant is applied. The protected areas remain smooth alongside the more grainy texture that is left where the aggregate is exposed. The effect is intensified when the pigment and/or cement colour contrasts with the sands and aggregates. As with all techniques, timing and skill are important for effective execution.
Shot or Grit Blasting
Shot or grit blastings 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. If intended to be a final finish, careful control is required to ensure consistency. A test patch is recommended so that the degree of the shot blast can be agreed. As with depth of polish, the heavier the abrasion, the larger the pieces of aggregate that will appear.
Imprinting Wet Concrete
Imprinting wet concrete is a common technique for creating texture in external concrete and can be a cost-effective way of improving slip resistance. A tamping beam is progressively lowered and raised along the face of the floor to imprint freshly placed and levelled concrete. This creates a surface with ridges, with their frequency and width depending on the size of the beam. It can be specified as light, medium or heavy tamp but these descriptions are not clearly defined and a benchmark or test panel is advised.
Brushed or Dragged Concrete
Brushed or dragged concrete is a similarly cost-effective finish for adding slip resistance and is useful for utilitarian areas where aesthetics are less important, due to the difficulty of obtaining a uniform finish. It does offer opportunities for pattern and variety depending on the direction of drag and the material used. Stiff bristled brooms give a coarser texture than those with soft bristles, for example. While actual sweeping brooms can be used, a purpose-made brush with steel bristles or tines is more appropriate for commercial applications. Other dragged surface finishes include ‘Turf drag’, ‘Hessian drag’ or ‘tine finish’ using different materials to create the texture as their name suggests.
An alternative method for adding texture to wet concrete is stamped or pattern imprinting using mats or rollers. Most commonly used externally, standard systems are most likely to be in the form of patterns with stone, cobbles or herringbone for paths and patios, but the technique offers opportunities for unique textures and patterns through the creation of bespoke mats.
The use of tamped, brushed and imprinted concrete on internal spaces may be restricted by the ability to gain access to create the finish in the wet concrete. This, therefore, requires consideration of sequencing early on.
Colour
The colour of a concrete floor will be determined by the through the colour of the mix, which will itself vary in appearance depending on the surface texture employed and how much of the aggregate is exposed. It is also possible to add different and permanent colour to the upper surface only of the concrete.
Dry Shake Toppings
Dry shake toppings are powder or granules broadcast onto the surface of the concrete before trowelling. Once trowelled into the floor, this results in a hard, durable surface. There is a wide range of coloured pigments available, including grey, and toppings can be selected to suit the specific performance requirements of the floor. 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.
Colour Stains
Colour stains can be applied to either trowelled or diamond-ground polished floors and offer the advantage of colour variety and a controlled application to create pattern, allowing the natural tonal variation of the concrete surface to show through.
