May 2019 DIY: HOW TO GET AN EXPOSED AGGREGATE FINISH ON CONCRETE
Course, textured and offering a one of a kind expression, Sephaku Cement explains more about an exposed aggregate finish and how this can be achieved.
Although it may take an experienced contractor to pull off the desired look, an exposed aggregate finish is responsible for creating some of the most unique and one of a kind appeals in concrete construction. Making use of carefully selected aggregate, an exposed aggregate finish adds depth, texture and a unique feel to an otherwise smooth and flat concrete finish. Over and above the appearance that exposed aggregate accomplishes, when used in sidewalk paving, garden pathways or even poolside decking, exposed aggregate concrete is extremely effective in achieving a non-slip solution to outdoor areas that can become slippery when wet.
While a standard concrete mix can be used, for best results special aggregates are incorporated to influence the texture and colour of the exposed aggregate finish. Achieving an exposed aggregate appearance takes experience, specialised skill and patience. Although a seemingly rudimentary process, it is in fact an intricate installation that requires care and attention during each phase.
Where the biggest challenge is accomplishing the correct depth when installing exposed aggregate paving, because the process is somewhat of a manual application, expert attention needs to be paid in order to achieve a uniform and even appearance.
With two methods used to achieve exposed aggregate, one way is to pour wet concrete mixed with course aggregate stones and then to wash the surface of the concrete installation before the concrete reached final set in other words strong enough to withstand the washing operation but not set too hard to not be able to wash out some small amount of paste from the surface of the concrete. Using either water or spraying the wet concrete with a retarding agent, in doing so will reveal the exposed aggregate stone a day after the concrete has been allowed to cure.
The second method used is achieved by surfacing placed concrete by applying course aggregate stone to pre-poured wet concrete mix. This method sees contractors adding carefully the pre-washed aggregate to already poured and still wet concrete in converse to exposing incorporated aggregate by means of “washing the surface”, as described above.
Carefully agitating and smoothing out the surface of the applied aggregate, by pressing the stone into the surface of the wet concrete your contractors will take extra care not to trowel the stones too deep into the concrete leaving just the right ratio of stone aggregate exposed. This method is extremely effective in controlling the depth of the installation while also allowing for and maintaining a secure bond between the aggregate and the concrete as the concrete cures.
Another important consideration to factor in, although not unique to the installation of exposed aggregate cement fitting, is the effect of freeze thaw and shrinkage of concrete. As you may well already know freeze thaw and shrinkage is the leading contributor to blemished and cracked concrete fittings, regardless of whether you are installing an exposed concrete or smoothed out finish. As is the case with all cement based applications, careful attention needs to be paid in taking into account the expansion and contraction of concrete and installing supportive measures (mesh and or joints) that will allow for this inevitable occurrence.