Since to err is human, we’d like to dedicate this blog post to some common mistakes made during the shotcreting process. Have any of these blunders ever caught your eye? Let us know in the comments.
1. Adding water in excess
A little while back we looked at the ultra-delicate water-cement ratio. You may remember that when this fragile relationship is altered, the quality of the concrete is compromised, resulting in reduced compressive strength and durability.
Was your concrete delivered with a faulty slump? This could be due to movement during transportation, or an erroneous mix design. The important thing to grasp here is that adding water is never the way to go, as this will alter the water-cement ratio, and not in a good way.
2. Dosing the accelerator uncontrollably
This goes without saying: additives play an essential role in giving concrete the properties that make it the most widely used material on the planet. While additives are typically added during the mixing process, accelerators are, in contrast, integrated immediately before spraying. But what happens when you fail to follow the recommended guidelines for additive dosage? It turns out that the concrete’s final resistance is altered, resulting in layers that don’t quite adhere to the surface.
Are you or someone you know the kind of person who likes add a little extra accelerator to achieve thicker layers, and then call it a day? Do think twice next time. The uninformed use of accelerators generates unnecessary costs, as they are the single-most expensive element consumed by the machine during the shotcreting process.
3. Forgetting to clean the surface
As is the case in many aspects of life, a clean surface is vital to ensuring an optimal application of shotcrete, for two key reasons: for starters, it helps to eliminate residue, which will boost shotcrete’s capacity to adhere to the surface; and secondly, it removes any loose materials, so that the support work you’re doing is on a stable structure (the principle of hydroscaling).
For a good overview of an optimal application of shotcrete, have a look at our blog post 9 rules for the art of shotcreting.
4. Thinking that you need added pressure
The pressure gauge has been known to throw off the odd operator.
Many shut off the collector valve in an attempt to get the compressor flow rate and pressure at a level they deem adequate for the job.
It turns out that, as a rule, compressors come with a fixed flow rate and not a variable flow rate, which means that all they’re achieving by shutting the valve is that the compressor work less efficiently and with a greater load. Takeaway: don’t touch the valve.
5. Thinking that your compressor doesn’t provide enough kinetic energy
What do you we mean by this? Well, that by thinking that your compressor isn’t powerful enough to carry out your spraying job, and by changing it for a larger one, you could be asking for trouble.
One of the main issues arising from this switch is increased rebound. By spraying the concrete at a speed greater than that which is needed, rebound is bound to happen. But worry not, we’ve got you covered with a series of tips for controlling your rebound rate.
Also, bear in mind that, nowadays, concrete spraying equipment is designed to come through in the kinetic energy department. The compressor itself comes with a predetermined flow rate while the machines come with a nozzle that’s apt for the job. If you’re spraying at a correct distance, there’s no reason why your shotcrete job should disappoint.
Do you know of any other common mistakes made when applying shotcrete? Let us know!