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Blasting and Surface Preparation

Preparing steel and other surfaces for new coatings often calls for abrasive blasting first to remove previous paint, mill scale, rust, or contaminants. Experts estimate that as many as three-quarters of coating failures occur because of inadequate surface preparation.

Abrasive blasting uses a controlled flow of abrasive mixed with compressed air delivered to the surface of the substrate to clean the surface and leave a profile. The type of abrasive used varies with the job but can be coal slag or other sand substitutes, steel grit, garnet, and others. Sponge media combined with one of a variety of abrasives available produces very little dust and can also be recycled. Vacuum blasting is also an option for media capture.

The profile is the angular roughness of the surface that coatings can grab onto, and, in general, the greater the surface profile—the peaks and valleys of the micro-indentions in the substrate—the better the coating will adhere to it. Following the recommended industry standards for the surface profile of the substrate and the coating system gives the best chance for a successful paint job. Here is a brief rundown of the blasting we perform:

Surface Preparation

Various methods are employed to prepare surfaces for painting, coating application, and other procedures. Whether performed chemically or mechanically, ensuring the complete removal of previously applied coatings, surface imperfections, oxidation, organic matter, residue, and other contaminants must be done to prepare substrate before coating application.

Proper surface preparation is crucial for the success of industrial painting. This may involve cleaning, sanding, or using other methods to ensure that the surface is free of contaminants and properly readied for the application of coatings.

Different methods can be utilized to ensure successful surface preparation. However, they all tend to follow the same process.

Surface Condition Assessment

Before we begin the surface preparation process, we must perform what's referred to as a surface condition assessment. A surface condition assessment tells our painters what condition the surface is in, what techniques will be required for the preparation, and if the preparation process will be successful. Standards are a tool that can be used to assist with the assessment, as they provide guidelines for rust grading and other ways to measure surface profile.

Old Coating Removal

Once the surface condition assessment has been completed, we will continue removing any old coating. Careful consideration must be given before applying a new coating over the old coating, as this can allow preexisting conditions like peeling, flaking, and bubbling to continue beneath the new and old layer. Stripping old coating goes a long way to ensure preparation success by abating an underlying issue such as corrosion and thereby extending the life of the material.

Removal of Oils, Chlorides, Acids, and Other Surface Contaminants

It's not just old coatings that require removal from a material's surface. Within industrial settings, substances like oils, grease, and lubricants regularly land on and cover the surfaces. These must be eliminated to maintain the bond strength between the substrate and the new coating.

Additionally, chlorides may accumulate on a material's surface, particularly in areas near the sea or marine environments. The presence of chlorides can accelerate the oxidation rate in metals in a condition known as chloride-induced corrosion, leading to quicker corrosion damage.

Sometimes, it's necessary to perform testing to verify the presence of these contaminants because they're undetectable to the human eye.

Removal of Loose Oxides of the Surface

We also clean the surface of the material to remove any loose oxides that may come off by flaking or crumbling. Abrasive blasting is one technique that can effectively remove loose oxides, such as mill scale and rust from the substrate surface.

Surface Profiling

After clearing away any loose materials and other substances from the surface, we follow up with the crucial step of surface profiling. Sometimes, new coatings call for a different surface profile compared to the original coatings. To enhance adhesion and mechanical bonding, a profiled surface must be properly customized to the coating process and material.

Surface Drying

Lastly, we must wait for the surface to dry before we begin coating. A dry surface is best for most coatings moisture can inhibit the curing process. There's also the issue of flash corrosion, where bare metal surfaces are exposed to moisture. If the corrosion spreads beneath the surface of the fresh coating, you've got a real problem.

Additionally, humidity and dew point can cause problems as well. It's always a good idea to check if the environment's humidity level and dew point are compatible with the coating.

Types of Abrasive Blasting

Abrasive Blasting

The abrasive blasting process combines pressurized air with an abrasive material, which is propelled onto the surface of steel to remove paint, rust, and contaminants. Abrasive blasting can also be used on concrete and iron to remove discoloration, laitance, and other marks, as well as on brick and masonry to clean it.

There is more than one kind of abrasive blasting, but they all use pressure (air pressure, water pressure, or centrifugal force) to power an abrasive stream at the blasted surface. At Vulcan Painters, we have professional experience in wet blasting, dry blasting, vacuum blasting, and centrifugal blasting, as well as knowledge of what kind of blasting is best for a specific surface or material. We safely use abrasive blasting to effectively prepare surfaces for industrial painting and other treatments.

Dry Abrasives

Dry abrasives used in surface prep include sand, coal slag, steel grit, and garnet. Dry blasting media are sometimes combined with sponge media to reduce dust at the site of the blast.

Vacuum Blasting Systems

Vacuum blasting systems, also known as dustless blasting or closed-loop abrasive blasting, capture and collect the blast media inside the machine instead of releasing it into the air. This helps minimize the amount of dust and debris emission, making it more environmentally friendly.

Similar to the traditional abrasive blasting method, vacuum blasting involves the projection of abrasive media (such as coal slag, garnet, or other suitable materials) by way of compressed air onto the surface that needs cleaning or preparation. The abrasive particles strike the surface at high speed, removing contaminants, coatings, or corrosion.

Simultaneously, while the blasting process is happening, a vacuum system is used to capture and contain the debris from the surface, dust, and spent abrasive. This system creates a closed-loop environment, preventing the release of contaminants into the surrounding air.

The vacuum system is designed to contain the abrasive media and debris, allowing for efficient removal and disposal. This containment aspect makes vacuum blasting especially advantageous in situations where minimizing environmental impact and controlling airborne dust are critical.

Some vacuum blasting systems are equipped with recycling capabilities, allowing for the separation and reuse of the abrasive media. This feature contributes to cost savings and reduces waste.

Water Blasting

Water blasting uses high-pressure water with abrasive blasting media to reduce dust and remove coatings, debris, old paint, rust, scale, and contaminants from surfaces or cut through different materials. This method is also known as water jetting or water abrasive jet cutting. This technique is often used in industrial applications where precision, cleanliness, and the ability to cut through hard materials are essential.

The process begins with injecting abrasive materials into a high-pressure water jet. The water and abrasive mixture is expelled through a specialized nozzle that can be adjusted to control the size and intensity of the water jet. Different nozzle configurations are used depending on the application, such as surface cleaning, coating removal, or precision cutting.

Compared to traditional abrasive blasting methods, abrasive water blasting is often considered more environmentally friendly because it produces less airborne dust. The water helps contain the dust, reducing the risk of contamination in the surrounding area.

This technique is versatile and can be used for various applications, including the industrial cleaning process, surface preparation, coating removal, and precision cutting in industries such as construction, manufacturing, and aerospace.

Bristle Blasting

Bristle blasting utilizes a hand-held power tool with high-tensile steel wire bristles to remove contaminants and create a surface profile. This blasting method is often used for removing corrosion, coatings, and contaminants from metal surfaces, and it can be an alternative to traditional abrasive blasting methods. Bristle blasting is known for its ability to provide a clean and textured surface without generating dust, making it suitable for various industrial applications, including spot repairs.

Compared to some traditional abrasive blasting methods that generate dust and may involve using abrasive materials, bristle blasting is considered relatively environmentally friendly. It produces minimal airborne contaminants, reducing the need for containment measures.

Another advantage is its dust-free operation, making it suitable for applications where airborne dust could be a concern. Bristle blasting can also be used on a variety of metal surfaces, including steel, iron, and aluminum.

Shot Blasting

Shot blasting is a surface preparation technique that involves the use of high-velocity particles (shot) to clean, profile, and prepare a surface. This process is commonly used in various industries for tasks such as removing paint, rust, scale, and contaminants and providing a textured surface for coatings or treatments. Shot blasting is effective for cleaning and preparing surfaces in a more controlled and efficient manner compared to manual methods.

The blasting media used in shot blasting consists of small, spherical particles typically made of steel, cast iron, or other materials. This shot is propelled at high speeds to impact the surface being treated.

The shot is propelled onto the surface by either centrifugal force in wheel blast machines or by compressed air in air blast machines. Wheel blasting is more common and uses a rotating wheel to throw a shot into the workpiece.

Types of Shot Blasting Machines

Wheel Blast Machines (wheel blasting): these machines use a rotating wheel to propel the shot.

Air Blast Machines: the shot is propelled by compressed air.

Tumble Blast Machines: workpieces are placed in a rotating drum, and the shot is propelled inside the drum.

High-Pressure Water Blasting

High-pressure water blasting uses water only, at high pressure, to clean surfaces. The water pressure is usually between 700-1700 bar. As the water comes into contact with the surface, it removes any contaminants through high kinetic energy. This blasting method is reserved for use on blasting jobs that require high force, but for coating removal, abrasive material is not required.

Other Blasting Methods

Grit Blasting

Grit blasting is the general term for cleaning a surface or creating a profile on a hard surface. The term grit refers to using angular or sub-angular abrasive media specifically.

Wet Blasting or Vapor Blasting

Wet blasting is a favored blasting method for maritime and outdoor applications because it is a low-dust blasting option. It's important to note the possibility of "flash rusting" on ferrous surfaces when utilizing wet blasting, and the surface needs to be treated with a rust preventative.

Blasting Equipment

There are multiple pieces of blasting equipment used in the blasting process, whether it be wet blasting, soda blasting, dry blasting, dry ice blasting, bead blasting, or sandblasting.

Blast Pots

A blast pot or blasting pot is a pneumatic machine filled with types of abrasive that is fed high-pressure air by an air compressor. The pot functions as an abrasive container, holding the abrasive until it is expelled through a blast hose that the operator controls.

Vulcan Painters has the trained craftworkers and the equipment to complete your abrasive blasting job correctly and professionally. With dozens of trained blast operators to blast to customer specifications as established by AMPP and NACE, our staff has the know-how to transform a surface into one that is ready for coating application. Our Protective Coatings Specialists (PCS) are experts at helping select the best combination of blast specification and coating system for your project.

Contact Vulcan Painters for all your industrial painting and abrasive blasting needs, big or small. To get started, simply fill out the form on our website, call us (205.428.0556), or request a quote.