When Sydney builder Paul Meehan wanted to create a chessboard pattern on the floor of his games room, his first inclination was to go for tiles. But after talking to a concrete supplier, he opted instead for a polished concrete finish. And the unique and attractive result is, he says, well worth the effort. “It’s superb. Everyone who sees it is very impressed,” he says.
The chessboard pattern was achieved by inlaying 235 x 235mm jarrah timber squares into a concrete topping layer over the top of the existing slab, then grinding and polishing the top surface to expose the aggregate in the concrete.
The jarrah squares alternate with polished concrete squares to create the chessboard effect. Elsewhere throughout the 8 x 7m gamesroom, the concrete floor has been machine ground to continue the polished, exposed aggregate effect. Meehan also used the opportunity of laying the unbonded concrete topping to integrate in-floor heating.
According to the Cement and Concrete Association of Australia (C&CAA), more designers and builders like Paul Meehan are experimenting with exposed concrete as a flooring finish.
The C&CAA’s Eric Lume says the variety of creative finishes that can be achieved is virtually limitless – from simple trowelled ‘grey’ concrete finishes to sophisticated patterned and coloured effects. But aside from aesthetics, he says there are significant practical advantages in exposed concrete flooring, particularly in residential applications.
“It’s low-cost, durable, energy efficient, easy to maintain and - from an environmental perspective – doesn’t harbour dust and mites to the extent of more traditional floorings,” Lume says.“In terms of energy efficiency, concrete slabs are cool during the summer, and with the addition of in-floor heating running from off-peak power, provide a cost-efficient and highly effective heating system.”
Lume says there has also been “huge growth” in exposed concrete flooring in cafes and restaurants. “Because there are no tile joints, it’s easy to keep clean and free of bacteria. And, of course, it’s very hard-wearing.”
Concrete floor finishes have come a long way in recent years with the development of new techniques and treatments. Modern finishes include liquid polishes, latex coatings, chemical sealers, grinding to expose the aggregates, colours, stains and the use of special aggregates to achieve ‘rock’ or ‘marble’ appearances.
Some polished and/or coloured concrete finishes are achieved with an additional layer of concrete over the slab. This layer – or screed – can be added either when the slab is still ‘plastic’, or after it has hardened.
The simplest finish effect is achieved by steel trowelling the concrete surface, either by hand or using a powered trowelling machine known in the industry as a ‘helicopter.’ For smoother surfaces free of trowelling marks (often referred to as burnished finishes) power trowelling is required.
Exposing the aggregate in the concrete creates an unusual textured surface pattern. This is done by progressively grinding the surface, using finer and finer grinding pads, to bring out the aggregate. At the same time, this process results in a highly polished surface finish. In some instances, special decorative aggregates are used in the concrete mix, such as marble, plastic and glass.
Some ready-mixed concrete companies are taking advantage of the growing market for exposed aggregate concrete flooring by marketing a range of mixes that give the customer the flexibility to choose different colours and aggregates to achieve distinctive and unique concrete floors.
“One of the big advantages of concrete flooring is the flexibility it allows in expressing a truly unique design or pattern,” says Lume.“A whole range of materials can be cast into the concrete, from brass or zinc border strips and timber inlays, to cut pipe, natural stones, shells, tiles and artistic works.”
There are also a variety of ways of introducing colour into the finish. Colour additives can be used in the concrete mix, or alternately the surface of the finished slab can be treated independently. One method of doing the latter is by applying a dry shake topping, whereby colour pigments or pre-bagged mixtures are sprinkled onto the still wet concrete surface.
For existing slabs with a porous surface texture, another method is to apply a pigment to the surface. Yet another technique is chemical staining. Stains consist of metallic salts in a slightly acidic, water-based solution. The salts react with the hydrated lime in the concrete to form insoluble coloured compounds.
Once the desired coloured, patterned or polished surface texture is achieved, it is finished off with a sealer. Again, there is a range of options, from wax-based to chemical sealers. However, it is important to ensure that the sealer is appropriate for the floor and its application. For example, sealers used on paved driveways are not recommended for polished concrete floors because they may not readily absorb into the polished surface.
Lume says that when investigating different surface finishes, it’s important to discuss your requirements and desired outcomes in depth with your concreter.“Factors like flatness, level and texture can be critical in determining the quality of the finish,” he says.
For more information on polished concrete floors, contact the Cement and Concrete Association of Australia (C&CAA), or visit the website, www. concrete.net.au
Source: Building Products News.