All about Shotblasting
Do you want to know how Shotblasting works? What are the benefits & limitations and when should it be specified? Below is a short guide that will help you get an understanding of shotblasting.
Shotblasting is a process of blast cleaning concrete or steel surfaces. The shot is thrown at high velocity at the surface by a Blast Wheel which is spinning at high revs. The shot hits the surface hard enough to do two things:
- Hit hard enough to break of concrete and anything weak enough including contaminates away from the surface.
- To bounce back up after hitting the floor, up the curved rebound chamber, through the shot separation chamber then fall down to the shot hopper ready for use again.
Apart from using the best brand of shotblaster, the most critical to success on these is the Dust Collector.
If the vac does not have the ability to consistently provide enough flow, the shot will get dirty in a minute or two and then the shotblaster has NO hope of running smoothly. Plus dirty shot wears out the machine liners and blast wheel faster.
The basic principles of shot blasters are.
- Shot does not get sucked up by the dust collector. it rebounds off the floor up the rebound chamber.
- The dust collector is there to clean the shot as it falls as a curtain from the top separation chamber down to the shot hopper. Therefore, the dust collector must have enough airflow to pull the contaminates and the dust from the shot but not too much flow. Too much air flow will cause the shot to also be pulled out of the separation chamber and into the dust collector rather than continue to fall into the shot hopper of the shot blaster
- Always run the machine at full rated load this is normally indicated by an amp gauge. The rated load is normally written beside this gauge.
- Change the travel speed to adjust the blast intensity.
- Shot Blasters are only able to throw a certain about of KG per minute. Larger shot has a lot less balls per kg than smaller shot. increasing shot size will not necessarily increase speed. in fact, often the opposite. S330 is a great starting point for most blasters. try one size larger if the shot won’t rebound (bounce) properly.
Anyone using a shotblaster should have training in the use of a shotblaster. Floorex offers this along with every sale which includes:
- Training on how to set the correct flow of shot onto the blast wheel
- Training on how to replace and set-up the blast wheel and control cage.
- Training on how to be able to check and replace the wear liners.
- Training on how to correct issues that can arise.
Shotblasting is a highly effective way of preparing most floor surfaces, very efficient, very fast.
ShotBlasting – What are the benefits?
Shotblasting is highly beneficial to any contractor who needs to prepare floors to give the ultimate anchor pattern for floor coatings, screeds and indeed, smart polished concrete contractors who want to massively reduce the time taken to grind down to the aggregate.
The secret is to have had right training so you understand what the right preparation for the given job is.
Golden Rule: Use the smallest shot that will get the job done!
The reason for this is:
- Smaller shot will blast faster, much faster. You will do more square metres per hour, because there is a lot more pieces of shot per kilogram.
- You won’t take out un-necessary depth of concrete, which only wears out the blast wheel and wear liners un-necessarily, and means more coating or screed to fill it.
- In the case of a coating; a beautiful fine blasted finish will cover nicely, but an over blasted surface will increase costs to fill the profile with epoxy if you use the wrong shot.
- Obviously, if you need to create a bigger profile for any reason then bigger shot is the way to go. But still, the same rule applies; use the smallest shot that will give you the profile in the best time.
Shotblasting has the advantage that it is far faster and less cost per square metre to prepare floors and give excellent adhesion. Many coatings contractors will shot blast lightly, then diamond grind lightly, to get excellent finish and give your customer the ultimate adhesion on the job. It’s faster, quicker and less cost.
ShotBlasting – What are the limitations?
There are very few limitations that apply to shotblasting; that is why it is the ultimate preparation method – when it is done properly
- in low traffc areas such as pedestrian areas where a thin coating is to be applied,shotblasting may leave too much profile (roughness) show-through, e.g. in a car showroom, especially if the concrete is weak.
- won’t level up a floor; it will remove just as much off a high area as a low area.
- can’t remove many coatings, especially thick elastomerics and glues etc. Can work very well on many thin coatings. Thick epoxies may cause deep profling of the floor.
ShotBlasting – When should it be specified?
Sadly many projects today that ought to be shotblasted are prepared by other means; This is usually because:
- The benefits are not entirely understood.
- Shotblasting to the same depth of removal is cheaper than diamond grinding
- Shot Blasting delivers better profile and adhesion
- Shotblasting assures you of removal of all surface contaminates.
- The specifier has had a bad experience because a previous project was damaged by over blasting, or similar problem.
- The specifier received advice from a contractor who, while he may know a lot; he has learnt his trade by default, or has only got other machines such as diamond grinders and can’t offer shotblasting.
ShotBlasting – Floor surfaces that ought to be ShotBlasted and Why!
Here is a brief list of floor surfaces that ought to be ShotBlasted and why.
- Food Factories
- Abattoirs
- Bakeries
- Fruit Juice & Dairy Product Factories
- Chemical/Oil Bunds
Many of these factories use trolleys & pallet trucks that have hard wheels; such as cast iron or hard nylon. These wheels pound the surface as they are rolled. Any weak concrete is likely to be pulverised. Naturally, coatings bonded to pulverised concrete is going to lift.
Shotblasting removes weak concrete, because it blasts all the surface indiscriminately. Diamond grinding can leave weak areas because it only works in a flattening action – below the level you have ground down to, there can be more weak areas not removed by the Diamond Grinding.
Contamination in food factories is a major problem. Food acids, animal or vegetable fats/oils must be removed. Diamond grinding has the disadvantage that contaminates are rubbed back into the surface after they are ground off. If you grind long enough, and preferably in several layers, it is possible to grind deep enough to have a reasonable assurance that contaminates are sufficiently removed, but this invariably costs a lot more.
Shotblasting breaks the top surface away and contaminants are actually removed and extracted. The shot is usually very close to contaminate free before it is reused.
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