Shotcrete, specifically the wet mix process, has been used in construction projects in Australia since the 1960’s. There are lots of applications of shotcrete, like swimming pools, basement walls, and slope stabilisation to name just a few. One of the underlying limitations of shotcrete is the aesthetic appeal of the surface finish. If left in its natural state, or ‘gun finish’, the end product can look somewhat sloppy and unattractive, particularly if used on a large scale. In addition to this, using poorly qualified shotcrete providers with low quality materials may result in an eyesore which is very costly to repair.
Leaders in the shotcrete industry are well aware of this issue and have therefore developed a range of finishes that are much higher quality than the standard gun finish. There are many levels of finishes available, generally by adding an additional step onto the previous method, at additional costs to the customer. Some of the finishes available include steel trowelled, simulated rocks, and coloured finishes, and today we’re going to take a closer look at each of these finishes and what processes are involved to achieve them on vertical walls.
The gun finish happens when the shotcrete sets naturally after being applied to a receiving surface. This undisturbed natural finish doesn’t look appealing at all and no additional costs are involved. Typically, the gun finish will produce a surface that is fairly rough (except when a highly skilled nozzleman is employed), and the results bears resemblance to a pebbledash or stipple finish.
Once all the shotcrete has been applied, guidelines are set along the face of the wall and a screed is used to level the wall to the required line. Occasionally, aggregate marks can still be seen when using this approach, however a competent screeder with appropriate tools can make this finish look somewhat respectable.
Wood Float & Sponge Finish
Once the wall has been screeded, wood floats are used to close the face of the wall. After the shotcrete has been set but is still green, a sponge is used in the final stage to yield an off-render finish.
Steel Trowel Finish
The highest quality finish and therefore the most costly, is the steel trowel finish. This type of finish is very difficult to achieve due to the high level of craftsmanship needed, and only the most experienced shotcrete contractors are capable of achieving these results. Once the wall has been screeded, the face is steel trowelled which produces a glassy smooth finish. The reason why this finish is challenging is because all the work, including the crew, materials, prepping, and weather, must be perfect to achieve the desired results.
Oxides and Pigments
One option that is commonly used in shotcrete projects is adding coloured oxides and pigments to the concrete mix which can match the colour of the surrounding environment. The best results are normally achieved when the surroundings contain sandstone, rock, or soil, as the colour of the shotcrete can blend in very well. The only disadvantage of using this method is that if more than one batch is required to complete the finish, all the sands and aggregates used to create each batch must be identical, which is obviously hard to achieve. Consequently, shotcrete providers will typically request written acceptance that this may occur before they start any work.
Simulated Rock or Block Finish
On the most interesting shotcrete finishes available is when shotcrete is mixed without using coarse aggregate. This allows contactors to cut, mould, and colour the shotcrete so it looks like rocks, shale, sandstone or blocks. The results are so impressive that the finished product doesn’t even look like shotcrete and blend in very well with the natural environment. These finishes are found extensively in landscaping work such as simulated rocks next to backyard swimming pools.
As you can see, there are many levels of shotcrete finishes besides the natural finish which are available to customers to create aesthetically pleasing results. Even though the costs for projects with extra finishes will be increased, the most essential variable to consider is the quality of the shotcrete provider. It’s integral that you ask for proof of experience and evidence of other work they’ve performed for you to assess their skills and avoid getting ‘stuck’ with a second-rate product!
If you’re interested in using any of the above finishes in your next project, reach out to Evolution Shotcrete by phoning 07 5561 8885. We have the best shotcrete equipment as well as expertly trained engineers and workers available for shotcrete projects all over Australia.