If you’re here, you’re probably curious about what goes into blast cleaning.
Where did the concept of blast cleaning come from? When is blast cleaning generally required? What materials are used in the blast cleaning process? It’s all really quite interesting – well, we think so anyway!
So let’s strip it all back to basics – it’s kind of what we do…
What is blast cleaning and how does it work?
Blast cleaning is a process that is used to clean coatings or dirt by propelling a crystalline, sand-like material (such as soda crystals or crushed glass, called the “blast media”) onto a surface at high pressure – generally using compressed air. This pressurised application causes friction on a miniscule scale, causing just enough of an impact that the unwanted coating comes away, whilst leaving minimal to no damage to the substrate underneath.
Blast cleaning is particularly useful in vehicle restoration and property maintenance. Its automotive uses involve removing paintwork, dirt, filler and grease from both internal and external components. In terms of property management, blast cleaning can be used to remove paintwork, varnish, environmental staining, and graffiti from stonework, brickwork, and wooden or metal beams.
Blast cleaning is sometimes also called “abrasive cleaning”.
What is the history of blast cleaning?
The concept of blast cleaning has been around for a surprisingly long time. The first blast cleaning machine was patented in the USA by Benjamin Tilghman in 1870; it used a mixture of sand and water propelled at a surface to remove rust or paint. The invention was developed further in 1904 by Thomas Pangborn who incorporated compressed air to make it more compatible with metal surfaces.
Since then, the machinery and techniques have become more and more sophisticated. Blast media has also changed over the years; using sand in abrasive cleaning was outlawed in the 1980s due to the silica in sand presenting a risk of silicosis to blast cleaning operatives.
Soda started to be used as an abrasive blasting medium during the 1980s; the 1984-86 restoration of the Statue of Liberty included an early, notable use of soda blasting.
What are the most common blast cleaning media in use today?
Here at SBL, we use all of the most common blast cleaning media, including bicarbonate of soda, crushed glass, and vapour blasting. We also use two less common medias now and again too – aluminium oxide and crushed garnet. We also use a pressurised steam cleaning system called ThermaTech® for property restoration.
Soda blasting is by far our most commonly used abrasive cleaning method. Bicarbonate of soda crystals are propelled at a surface at high speeds using compressed air, impacting the surface and removing unwanted coatings.
Soda provides the gentlest clean out of all of the methods listed below. Firstly, it causes little to no noticeable damage to the substrate underneath, making it perfect for cleaning graffiti from brickwork, stonework, and wooden beams – even those that are Grade II listed.
Soda is also particularly useful in automotive restoration; because soda blasting generates absolutely no heat, it makes light work of more delicate metal components and those that are prone to warping. Soda blasting is particularly useful when it comes to cleaning aluminium components (which may otherwise be prone to heat damage) and fibreglass panels (as it won’t disturb the gel coating encapsulating the fibreglass moulding).
However there is one drawback to using soda blasting for automotive purposes. It leaves a rather dull finish on metal, so it’s only really used when the surface is being repainted or otherwise covered up.
Glass blasting is probably our second-most used method. Crushed glass particles are blasted at the surface using compressed air. Glass is a much hardier blast media than soda, so the friction present can cause heat to accumulate. This limits its potential for automotive uses as large flat components like bonnets, roofs, and doors may warp under high temperatures. However, this harshness does provide a slight benefit for property development – when used on hardwood beams or brickwork, glass blasting does provide a rougher, more rustic appearance that some clients prefer.
Vapour blasting – also called “aqua blasting” – involves blasting the item in question with a slurry of crushed glass and water. As well as removing dirt or coatings, the process also leaves a soft, satin-like sheen to most metals.
Vapour blasting is a popular process, but it does have a couple of drawbacks. Firstly, ferrous metals can’t be cleaned using aqua blasting or they’ll rust. Secondly, vapour blasting takes place within a specially designed safety/recycling cabinet that both protects the operative and recycles usable spent media. Vapour blasting cabinets are around 1m3 in size, so anything larger will need to be cleaned using another method.
ThermaTech® (Pressurised Steam)
ThermaTech® is a specialist masonry and stonework cleaning system, developed by Restorative Techniques Ltd. Rather than propelling a crystalline blast media at the surface, this system applies pressurised, superheated steam to remove paint, graffiti, environmental staining, mould, and mildew. Think of it like a household pressure washer but one that uses intense heat and operates at a higher pressure.
One downside of ThermaTech® is that we’ll occasionally have to use potentially harmful chemical primers and strippers beforehand to assist with the cleaning process. These are generally applied and cleaned away the same day to minimise any risk to people or to wildlife; we always collect any potentially hazardous detritus and dispose of it at our facility. We do our utmost to only use these primers only where absolutely necessary.
Aluminium oxide is a durable grit that generally provides a very similar finish to soda blasting. Like vapour blasting, the media can be reused a number of times before needing to be discarded, so we generally use it within our safety/recycling cabinet so it can be recycled. Therefore, we only use aluminium oxide on smaller items that fit in the cabinet. We don’t use aluminium oxide very frequently, but under some circumstances it can be the best option.
We know what you may be thinking – yes, we’re talking about the precious gemstone garnet. Garnet is an incredibly hardy material, much tougher than crushed glass. Crushed garnet (usually derived from Almandite or Andradite deposits) is often used in industrial cleaning projects where metal surfaces need the toughest battering we can provide. It’s so abrasive that we would never use it on thinner metal items such as automotive parts and bodywork – that’s a surefire recipe for heat warping!
We hope that this has been an interesting read! Join us in a forthcoming blog post where we’ll examine the practicalities of blast cleaning – including what the process looks like, health and safety considerations, as well as how we generally set up for work and tear down when we’re done.
And of course if you need blast cleaning services, we’re your crew!