What is Sandblasting?
Sandblasting — also known as abrasive blasting — is a surface preparation process that uses high-pressure compressed air to propel abrasive particles against a surface, removing rust, scale, old coatings, and contaminants.
Despite the name, actual sand is rarely used in modern abrasive blasting. Crystalline silica dust — which is produced when natural sand fractures on impact — poses serious respiratory health risks and is tightly regulated in New Zealand under workplace health and safety legislation. Professional blasting operations now use a range of engineered abrasive media that are both safer and more effective than sand ever was.
Surface preparation is widely regarded as the single most important step in any coating or painting process. No matter how good the coating material or how skilled the application, if the surface underneath is not properly prepared, the finish will eventually fail. Contaminants, rust, mill scale, and old coatings all interfere with adhesion. Abrasive blasting removes these completely, leaving a clean surface with the right profile for the new coating to grip onto.
At Coating Lab in Onehunga, sandblasting is a core part of our operation. We use it as the first step for items that require thorough surface preparation before powder coating, wet spray painting, or zinc arc wire spray application.
Media Types Used in Modern Abrasive Blasting
The term 'sandblasting' is generic — the actual abrasive media varies depending on the surface material, desired surface profile, and application.
The choice of abrasive media depends on the material being blasted, the condition of the surface, and the desired surface profile. Each media type has distinct characteristics that make it suited to particular jobs.
Steel grit and steel shot are among the most common media for heavy-duty work. Steel grit is angular and aggressive, making it effective for removing heavy rust, mill scale, and thick old coatings from steel fabrications. Steel shot is rounder and produces a smoother, peened finish. Aluminium oxide is another hard, angular media that cuts efficiently and is used when a clean, sharp surface profile is needed on steel substrates.
For softer or more delicate work, glass bead media produces a smooth, satin-like finish and is commonly used on stainless steel and aluminium where a less aggressive profile is required. Garnet is a natural mineral abrasive that offers a good balance between cutting speed and surface finish, making it suitable for precision work. Softer media such as crushed walnut shell or plastic beads can be used on substrates where steel abrasives would cause damage.
The right media selection is a key decision that affects both the quality of the surface preparation and the performance of the subsequent coating. Our team selects the appropriate media based on each job's requirements.
Applications and Common Uses
Sandblasting is used across a wide range of industries wherever surface preparation or cleaning is required.
Rust and corrosion removal is the most common reason items are sandblasted. Steel structures, fabrications, and fittings that have been exposed to the elements — particularly in Auckland's humid, coastal environment — often develop significant surface corrosion that needs to be fully removed before any new coating can be applied.
Removing old paint and failing coatings is another frequent application. When an existing coating has broken down, peeled, or failed, blasting strips it back to bare metal so the new coating system can be applied to a clean, properly prepared surface. This is far more thorough than sanding or wire brushing, which can leave contaminants behind.
Sandblasting is also used to prepare bare steel that has never been coated. New fabricated steel typically has mill scale — a hard, flaky oxide layer from the manufacturing process — that must be removed for coating adhesion. Beyond these core uses, we regularly blast castings, architectural metalwork for restoration projects, and automotive and motorcycle components being rebuilt or refinished.
When is Sandblasting Required?
Not every item that comes in for coating needs to be sandblasted, but there are situations where it's the only appropriate method.
Heavily rusted items almost always need to be blasted. When corrosion has progressed beyond light surface rust into pitting and scale, chemical cleaning alone cannot reach deep enough to remove it all. Blasting gets into every pit and crevice, giving you a genuinely clean surface to work with.
Items with existing coatings that need complete removal are also candidates for blasting. If the old coating is thick, multi-layered, or has failed in multiple areas, blasting is the most efficient way to strip it back to bare metal. Similarly, new fabricated steel with mill scale must be blasted if the coating specification requires it — many industrial and protective coating systems specify a blast standard such as Sa 2.5 (near-white metal) as a minimum requirement for adhesion.
There are situations where blasting is not required. New, clean metal that is free of rust, scale, and contaminants may only need a chemical degrease and pre-treatment before coating. Our team assesses every item that comes in and recommends the appropriate preparation method. The goal is always to achieve the best possible coating adhesion and longevity for the specific item and its intended use.
Safety Considerations
Abrasive blasting involves high-pressure equipment and fine particulates, making safety a primary concern.
The primary hazard in abrasive blasting is airborne dust. When abrasive media strikes a surface at high velocity, it generates fine particulates that can include metal dust, old coating fragments, and spent media particles. Inhaling these particles is a serious health risk, particularly over repeated exposure. This is why professional blasting is carried out in contained environments with proper extraction and filtration systems, and operators wear full respiratory protection.
Noise is another significant hazard. High-pressure blast equipment generates noise levels well above safe exposure limits, making hearing protection essential for anyone in the vicinity. The combination of dust, noise, and high-pressure equipment is the main reason DIY sandblasting is impractical and hazardous for most people. Without proper containment, extraction, and personal protective equipment, the health risks are considerable.
At Coating Lab, blasting is carried out in a dedicated blast area with containment and extraction systems designed to manage dust and spent media. This ensures a safe working environment for our team while also preventing abrasive dust from contaminating other areas of the workshop or the surrounding environment.
Sandblasting as Part of the Full Coating Process
At Coating Lab, sandblasting is part of a complete surface preparation and coating service — not a standalone process.
Sandblasting is most effective when it is part of a complete surface preparation and coating workflow. Once an item has been blasted back to bare metal, it needs to be coated promptly — exposed bare steel will begin to flash rust within hours in humid conditions. Having both blasting and coating capabilities under one roof means items move directly from preparation to coating without delays or transport that could compromise the freshly prepared surface.
At Coating Lab, we offer sandblasting as part of our full coating service. Whether your item is being powder coated, wet spray painted, or receiving a zinc arc wire spray application, the blasting and coating happen in the same workshop. This reduces handling, eliminates transit risk, and ensures the coating goes onto a surface that has been prepared to the right standard moments before.
When you request a quote, let us know the size and condition of your item, the type of coating you are after, and where the finished item will be used. This helps us recommend the right combination of surface preparation and coating for your project. You can drop items off at our Onehunga workshop or give us a call on 09 218 6436 to discuss your requirements.
Frequently Asked Questions
Sandblasting, also known as abrasive blasting, is a surface preparation process where small particles of abrasive media are propelled at high pressure against a surface. This removes rust, old paint, mill scale, and other contaminants, leaving clean bare metal ready for a new coating. It is the most thorough method of surface preparation available and is essential for achieving strong coating adhesion on items that are corroded, previously coated, or covered in mill scale.
Despite the name, actual sand is rarely used today due to health regulations around silica dust. Modern abrasive blasting uses a variety of engineered media including steel grit, steel shot, aluminium oxide, glass bead, garnet, and softer options like crushed walnut shell. The media is selected based on the material being blasted, the condition of the surface, and the surface profile required for the coating system being applied. Our team chooses the right media for each job to achieve the best result.
Not always, but in many cases yes. If your item has rust, old paint, mill scale, or other surface contamination, sandblasting is typically the best way to prepare it for a new coating. Items that are clean, new, and free of contaminants may only need a chemical degrease and pre-treatment. Our team assesses every item on arrival and recommends the appropriate preparation method. Skipping necessary blasting can lead to poor coating adhesion and premature failure, so it is always worth getting the preparation right.
The time required for sandblasting varies depending on the size of the item, the severity of rust or old coatings, and the complexity of the surface geometry. A small, lightly rusted component will be much quicker than a large, heavily corroded fabrication with intricate shapes. When you contact us for a quote, we can give you a better idea of the timeframe based on the specifics of your item. Give us a call on 09 218 6436 or request a quote online.