What is sandblasting?
The technique of sandblasting is relatively simple in principle: by means of pressurized air, an abrasive granulate is thrown against a surface. This has the effect of cleaning or stripping it. The practice is called “sandblasting”.
Either fixed or mobile, the sandblaster is connected to an air compressor. Thanks to the pressurized air, the granulate is sucked in and then sprayed onto the work surface with a gun similar to a paint gun. The blasting gun can be equipped with different nozzles, larger or smaller, depending on how precise the work you are doing needs to be.
Historically, this technique was used industrially or by professionals. Today, with the evolution of products and materials, it is possible to safely sandblast at home and still obtain very good results.
There are several sandblasting processes depending on the type of surface you’re working with and the amount of material to be removed.
Sandblasting is mainly used for stripping and therefore operates at high pressure. On the other hand, when you simply want to clean and preserve a surface or to work with more precision, you simply work with a lower air pressure.
What are the different types of blasters?
There are three types of sandblasters: vacuum sandblasting, pressure blasting, and sandblasting cabins.
The vacuum sand blaster is ideal for small projects or spot cleaning. The advantage of such a machine is mainly that it operates with a low airflow of about 250 l/min (litres per minute). It can, therefore, be connected to and used with a "small" air compressor. These are not particularly complicated machines.
At their most basic they are a bucket with a hose attached. They consist of a tank, known as a hopper, mounted on a wheeled chassis, a hose, and a sandblasting gun. The aggregate is pulled through the hose by the Venturi effect when the gun trigger is pulled and is projected in whatever direction you point the gun.
In order to work correctly, the hose must be relatively short, which means that it can’t work very far from the hopper. In turn, treating a large surface can be long and tedious and would require you to frequently stop and move the hopper.
The pressure sander is the professional model. It operates on a completely different principle. Rather than being drawn from an open hopper, the aggregate is held under pressure in a sealed tank. Pressing the trigger of the gun releases this pressure which carries the aggregate out with it.
The pressure and the output flow of the gun are regulated and constant allowing for powerful and intensive stripping. High-end pressure sandblasters allow for a number of adjustments, which of course make both high and low-pressure techniques possible as long as you make sure you have the appropriate nozzle attached.
The length of the hose is no longer a concern, which allows for greater mobility. However, the pressure sander requires significant air flow (minimum 3000 l/min) to operate properly, which means equipping (and having access to) a high-power compressor.
The sandblasting cabin is a home workshop sander. For indoor scraping or smaller projects, this is ideal. In the majority of cases, the sandblasting cabin is actually a vacuum or air-gun sandblaster enclosed in a "sleeve box". To operate it, you slip hands into the gloves fixed to the chassis of the cabin and watch your work through the window above them.
The sandblasting cabin, which is widely used in mechanics or glass work, has the advantage of being able to work precisely without making a big mess and of operating with a lower power compressor (250 l/min minimum). Some cabins offer the option of connecting a vacuum cleaner and have interior lighting for better visibility.
Choosing the perfect nozzle for the job
The nozzles are to sandblasting what brushes are to painting. Depending on the work you want to do, you have to choose the right one. Whether for high pressure or low pressure, the nozzles differ in the following characteristics.
The profile (Venturi or cylindrical) can be covered quickly since cylindrical nozzles, which are much less efficient, is rarely used since the appearance of Venturi nozzles.
The length of the nozzles can be chosen in a simple way. Shorter nozzles require a much higher airflow rate than longer ones of the same diameter, which necessarily means having a larger air compressor to achieve the same level of efficiency.
The internal diameter (expressed in mm) of the nozzles is important. If you plan to do a lower pressure project on a small surface with some precision, you will need a very fine abrasive granulate, starters. Your gun should be equipped with a nozzle with a diameter ranging from 2 to 3.5 mm.
If on the other hand, you are considering high pressure sandblasting, your abrasive granulate will need to be adapted to the work you are doing and therefore your nozzle should adjust to accommodate it, ranging from 4 to 12 mm. As a general rule, the larger the diameter of the nozzle, the greater the air flow required.
Where a vacuum blaster equipped with a 3 mm nozzle consumes about 250 l/min, a pressure blaster equipped with a 12 mm nozzle consumes 9500 l/min. When choosing your nozzle, make sure they work with your choice of air consumption.
The material also has its role in the quality of the nozzle. Tungsten carbide is actually the standard material used in blasting nozzles, its strength is fairly good but it is heavy and its lifespan doesn’t usually exceed 300 hours of use.
On the other hand, there are now different types of ceramic, silicon nitride and boron carbide, which have the advantage of being much lighter, solid, and having a much longer lifespan - between 500 and 700 hours.
How to choose aggregates
There is a multitude of abrasive aggregates of different sizes, densities, shapes. Let’s take a closer look at the three most common types.
The metal shot is ideal for scouring, rust removal, or surface preparation - before painting, for example. Its main advantage is its high abrasive power. This is also its main disadvantage because the shot does not allow for precise work and is not recommended for finishing. It is reserved for heavy stripping works. The shot is not recyclable, which is another major disadvantage.
Corundum is an excellent abrasive for surface preparation, it can also be used to remove rust or strip wood. Its particle size varies from 0.1 to 2 mm.
One of its advantages is its very high hardness which makes it release very little dust. It can be used with any type of blasting machine, low or high pressure. Corundum is recyclable, which is a major perk.
Glass bead is geared more towards cleaning, deburring, or surface finishing because it is a soft abrasive. Its particle size is very low, between 0.05 and 0.6 mm. Glass beads are ideal for use at low pressure. Their low particle size makes them ideal for low pressure work. Glass beads are also recyclable.
What other characteristics are there?
Just to help you in your comparison, a little reminder:
- The dehumidifier filter is provided to prevent clogging when using your blaster
- The pressure gauge allows you to know the outlet pressure for your aggregate
- The safety valve is designed to prevent any accident due to overpressure
- The volume of the tank determines the time of use. However, this is relative to the size of the nozzle. For a tank of 50 litres, for example, if you sand with a 4 mm nozzle, you will have a time X. Using an 8mm nozzle, on the other hand, will cut your amount of time you can work in half.
- The thread seal strip is similar to the Teflon used to seal plumbing screw connections except that there is nozzle mounting on a nozzle holder - in the gun. If you want to sand properly, every time you change nozzle you are supposed to put tape on the thread before you mount it so that everything is tight. In reality, and in bodywork in particular, if you have a strip in place that’s good, but if you don’t, you can do without and it works anyway. The only risk is that you lose a little bit of air pressure around the nozzle.
- The funnel is provided for filling the granulate vessel
- The gun generally resembles an improved valve and it is on this that the nozzle is mounted;
Final advice on use and maintenance
A sandblaster can be hazardous in many ways if misused. When you go to work, think about your health.
Today there are sandblasting helmets that will protect your head (your eyes, your airways, your skull). So, is there really a reason not to use one?
An apron and a pair of gloves are also welcome.
Same rules apply any time you use a compressor. For the noise, protect your ears with noise-cancelling headphones
would be perfect under your sandblasting helmet.
To avoid any accidents, it is strongly recommended to make sure that you are well informed about the pressures of use of your various pneumatic tools,
especially if you use a pressure blaster.
In addition, some compressors are subject to special regulations that require periodic inspection, as often as every 40 months. Many accidents occur due to rusty tanks or faulty pressure controllers or regulators.
Think about your safety.
For DIY enthusiasts interested in knowing how to choose the accessories related to air blasting machines, follow the advice of our editors and discover their Guides:
And to work safely: