Blasting Guide

Abrasive Blast cleaning is the most cost effective process for preparation of a surface prior to painting and is usually used where long-term protection is required. Anchor patterns are produced by abrasive particles propelled at high force onto the steel surface in either the wet or dry condition. Such processes use a wide variety of blasting media, either applied by a closed recirculating system or by open blasting.

A few things to remember prior to having an item or items abrasive blasted.

  • 1. All surfaces should be clean and free of oil and grease.
  • 2. Make sure the item you are having blasted is at least 3mm thick for hardened steel/alloys or at least 5mm thick for soft/mild steel. Any less than these measurements and you risk warping the surface or worse still, completely disintegrating it from the heat and friction caused by the blasting process - we can offer advice on these issues.
  • 3. For engine/machinery parts make sure the item is not too corroded so as to make it useless. It may still be repairable through resurfacing/machining after the blast process - we can offer advice on those issues.
  • 4. When having an item blast cleaned make sure it is free of any 'at-risk' parts such as wiring, bearings/seals, rubber/plastic items, gaskets, sheaths and tires, all of which can be damaged by the blasting process. We can remove and reattach these for you but it will incur an additional cost.
  • 5. Blast-cleaned surfaces are very reactive and begin to rust in a very short space of time, especially after wet blasting. Decide on the type of protection the surface requires prior to having it blast cleaned. We can help you decide on the best protection for your item.

Rust Grades on Steel

  • The level of rust typically determines the blasting required by a surface. The following is the industry standard for rust measurement.
  • Grade A : Steel completely covered in mill scale and little, if any, rust.
  • Grade B : Steel surface has begun to rust and the mill scale has begun to flake.
  • Grade C : Steel surface has the mill scale rusted away or is removable by scraping, little pitting is visible to the naked eye.
  • Grade D : A steel surface has the mill scale rusted away and has considerable pitting visible to the naked eye.

The Four Classes of Blasting

  • The following is an industry guideline of the levels of blast cleaning and the results expected.
  • 1) C1 Light blast cleaning, which removed loose mill scale, rust and foreign matter.
  • 2) C2 Medium blast cleaning (sometimes called 'commercial' or 'thorough' blast cleaning), which substantially removes mill scale, rust and foreign matter particles such that grey metal is visible.
  • 3) C2 1/2 This is referred to as 'near white' blast cleaning, which removes mill scale, rust and foreign particles to the extent that only traces remain in the form of spots or stripes and the cleaned surface shows varying shades of grey.
  • 4) C3 this is known as 'white metal' blast cleaning, by which visible mill scale, rust and foreign particles are entirely removed and the cleaned surface has a uniform metallic colour, but may show varying shades of grey when viewed from different angles.