RestoPrep Australia
Automotive Restoration Preparation Specialists
Blasting - Coating - Restoration supplies

Blasting Media

There are many other blast medias available and we have tried virtually all of them. As a basic rule, anything softer than steel will not remove rust, so it's a bit pointless on old cars, anything harded then steel will remove all paint and rust, but the harder the material the more risk of damage.

ANY media harder than steel carrys the risk of panel warpage, this can only be avoided by training and skill of the operator. It's not an issue in industrial work as the steel is often 3-10mm+ thick and you would really have to be a fool to damage something that heavy. However car panels are generally .7 - 1.2mm (depending on the make, model and age of the vehicle). Panels of this gauge are very light and easy to damage if you don't know what your doing. You can't expect someone who just blasted a box trailer to blast your roof skin without damaging it, to most industrial blasters it's just another chunk of steel, they don't care.

No mater where in the country you are, make sure your blaster loves cars. It doesn't mater if they say they have blasted heaps of cars before. Many blasters out there will tell you they have 5, 10, 20 years of experience, you have to question what that experience is on? Do they blast 1 or 2 cars a month and the rest of the time box trailers, out door furniture, bobcat buckets, steel frames and fence panels? At RestoPrep we ONLY blast cars (also motorbikes and small alloy boats upto 18'), each of our workshops can do up to 15 cars a month, plus hundreds of panels, wheels and other parts.

There are quite a few different blast medias out there, each have there own pros/cons. Below you will find an accurate description of each. You may well have read magazine articles, website tech articles, other blasters websites, or general comments on facebook that suggest infomation different to what you will read below, however we can assure you the following info is true and correct from our experience when it comes to blasting cars. Often magazine tech features are actually paid presentations and not unbaised info as they may seem. So without further ado:

Firstly what is the difference between abrasive and none abrasive blast media?

It seams that most blasters do not understand what these terms mean, as many businesses make statments about certin blast medias being abrasive or none abrasive. Well in short this term is only relevant in relation to the object your talking about blasting. E.g garnet is abrasive to steel, but it's not abrasive to diamond as diamond is harder. So soda blasting is none abrasive to steel, but it is abrasive to paint.

So to make sure the infomation we are giving you is understood in the correct terms, for our purposes we are talking about automotive blasting, so at this point we consider an abrasive media to be any blast media that is harder than steel and therefor when propelled by air (blasted) at a car panel it will remove paint, body filler and RUST, leaving the steel with a profiled or etched finish. A none abrasive media is anything softer than steel. It's safe to presume that any "none" abrasive media is still harder than paint and therefor abrasive to paint and body filler.
none abrasive blast media are effectively just like chemical paint stripper, they remove paint but not rust (so generally pretty pointless for most older vehicles).

How is the hardness of blast media rated?
As with any mineral the MOHs scale of hardness is one of the main international standard units of measurement.
Talc - 1 Diamond - 10, everything else fits somewhere in between. Vehicle panel steel is generally around 6, paint around 2.
The most common blast medias are as follows - inc their most common uses.

Garnet - The most commonly used media used for industrial blasting, steel frames, trailers, outdoor furniture and also commonly used on cars. Available in a variety of particle sizes from quite large down to a very fine grade suitable for glass etching. It is a good all round blast media as it is reasonably hard and heavy it is re-usable and cost effective. However most blasters who don't really care about your vehicle and don't realise that because of these properties it will also harden the steel of your panels. This hardening makes the panels harder to work, sends body files blunt quickly and generally make panel work harder than it needs to be, which costs you more at the panel shop.
(Rating on the MOHs scale - 7.5-8)

Steel shot - Possibly the most common blast media used by industrial blasters. Steel shot although softer than garnet on the MOHs scale of hardness, it is a much larger particle (similar to what you would find in a shot gun shell) and carries even more velocity. The finish left can be quite heavily pitted and highly likely to cause panel distortion, to the point where it will write off your car. (MOHs - 7)
Crushed glass - Our media of choice. Available in a range of grit sizes, crushed glass is ideal for automotive blasting. The particles are relatively light weight compared to all other abrasive blast medias. It is also only slightly harder than panel steel on the MOHs scale of hardness (6.5 vs 6). Combind these 2 key properties and you have a blast media that does not harden panel steel like garnet, the fine particle size leaves a very mild profile and ultimately dramatically reduces the risk of panel distortion when compared to all other abrasive medias. The glass has quite sharp edges and can quickly remove rubbery coatings and underbody sealers.
The glass leaves no residue on the panels. This of course is our preferred blast media for almost all the blasting we do. (MOHs - 6.5)

We started calling this "fine abrasive blasting" when we first started back in 2007 and it seams to have grown into a common term across the country (and even internationally). However we don't agree with businesses using that term when they use garnet or other heavy abrasives, even if they are using the finer grades. To us fine abrasive refers to both the particle size and the physical weight of the blast media.

Also Crushed glass is only blasted at 100psi (not 400-600 psi as we've seen claimed)

Ilmenite - Although not as commonly used these days, ilmenite is a very fine media and leaves quite a smooth profile on panel steel. Giving industrial blasters a false sense of success when using it to blast cars. Ilmenite is highly prone to distort panels as its fine metallic compound creates heat quickly. Another major issue is the residue left on the surface is very hard to remove, leaving a soot like coating on the panels which is near impossible to remove before priming. (MOHs - 7)

Staurolite / Star blast - Similar to garnet except only available in 1 particle size and it's a little bit harder. Commonly used for automotive blasting by industrial blasters. It leaves a rough profile on the panel, again like garnet will harden the steel making it harder to work with. (MOHs - 8)

Bicarb Soda - Now this is one that you would no doubt have heard of over the past decade. Your best to read our full page about soda blasting here . However for a breif outline read on. Soda is great for a lot of things, but cars are NOT one of them. Soda is softer than panel steel, which means distortion is imposisble, however that also means it is NOT abrasive to steel, so it will NOT remove rust. It will also leave an alkaline residue on your car that can react with acidic paints (most of them). When blasted wet (to reduce the dust) Soda micro polishes the surface of the panels, causing delamination issues down the track if the surface hasn't been hand sanded before priming (creating even more work), plus Soda blasting costs a lot more than fine abrasive blasting. (MOHs - 2.5-3)

Plastic - often called media blasting, this is a case of misguided people (inc businesses that use plastic) refering to it by the wrong name. Media is a broad name for all materials used for blasting. E.g garnet is a blast media, soda is a blast media, plastic is a blast media. So calling plastic blasting "Media" blasting is incorrect. So please if you hear someone refer to plastic blasting as just media blasting, correct them. Ok so back to plastic blasting. Very similar in results to soda blasting, except it doesn't have the undesirable residue. It doesn't remove rust so it effectively gives the same results as chemical paint stripper but without the mess. Plastic also does not have the micro polishing issues of soda. Though in our opinion in most cases it's a pointless excersise as most cars that need blasting will have rust that needs to be removed. Plastic, like soda blasting leaves you with more work to do AND it costs a LOT more than fine abrasive blasting. Of all the none abrasive blast medias plastic is the best, and our choice for specailised jobs. So we do use it, however not often and rarely for full vehicles. (MOHs - 3.5)

Walnut shell / corn husk - Again like soda and plastic they are none abrasive to steel, so they don't remove rust, but they also can not distort panels. Expensive when compared to fine abrasive blasting, the residue that could be left in cavities will absorb moisutre and encourage rust. Was a bit of a fad 10 years ago, not very common these days. (MOHs - 3.5)

Dry Ice - Just like soda, plastic, walnut, etc. Can't distort. Not very common anymore, requires large expensive specialised equipment. Some people think that it envolves water however it is technically a dry process as the dry ice is CO2, so after impact the particles turn to gas and evaporate. Good in that it leaves no residue, but expensive, doesn't remove rust and very uncommon these days.

Dustless blasting - Whilst not technically an actual blast media, it's a process that should be mentioned here with the other types of blasting. This new fad is essentailly the same as regular wet abrasive blasting that has been around for many many years, the difference is these blast machines are designed to add the water to the blast media in the pot, signifcantly reducing air bourne dust. Yet again a great feature for the blaster, but not so good for the car owner / restorer. The media used is actually the same crushed glass as we use in all our workshops, however adding water to it removes the ability to easily blow the left over media from your car. We have done trials with this setup personally and found the blasting result to be similar to our own, the clean up was a nightmare, wet glass trapped in the sills and cavities (promoting rust later on), when the wet glass dried it was rock hard like sandstone and found to be very hard to remove. The vehicle continued to leak water for 2-3 days hindering primer application and we found many areas to start rusting during that time as the rust inhibitor product added to the water before blasting is only effective it no other contaminets or airbourne moisture contact the vehcile between blasting, drying and coating. Again we see this as a product promoted to make the operator profits but not to benefit the vehicle restorer. From our personal experience an experienced blaster in an encloused dry chamber is the ideal process to acheiving a quality start to your restoration.

There are other types of blast media, however these are the most common forms that your likely to hear of.
Hopefully you now know a lot more about the options and how each one relates to automotive blasting. Also keep in mind we are talking purely about our own extensive experience in automotive blasting on this site, the above blast medias have great uses in other industries and in the right jobs are extremely effective.