An introduction to blast cleaning

Blast Cleaning is the process of treating a surface by propelling particles at high velocity towards it. This can have a range of applications from patio cleaning to artificially ageing stonework. Small power washers can be purchased or hired relatively cheaply for small jobs such as cleaning walls or stonework, although they may not be suitable for some types of organic staining.

This will require blasting with grit or a similar substance, although this is likely to remove layers of the material you are trying to clean as well as the dirt. If it is important for the surface to be preserved a chemical treatment may be more suitable.

Different Techniques

The two main factors that can be varied in blast cleaning are the type of particle that is “blasted” and the pressure at which this is done.

Pressure: The pressure can normally be adjusted during the job to ensure that only the desired layers of material are removed. Using a overly high pressure is inefficient in that more energy is used than is necessary and more particles will be used increasing cost and the amount of waste.

A small test area, ideally somewhere discrete, is chosen and used to find the exact pressure required for the job. If the surface that is to be cleaned or treated is not uniform, the pressure may need to be adjusted as the work is carried out. This is a difficult task and requires a highly skilled and experienced person.

Particle size and type: grit, water, co2 etc. – also have implications on cleanup.

  • Grit is the most traditional substrate used for blast cleaning. There are a wide range of different types however, each with different applications. The cheapest standard grit is suitable for cleaning heavily corroded steel, marine growth and cement build-up. It would also be used before a metal media is used to treat a surface. More expensive grits create a finer etch on the surface and give a more efficient clean in terms of time and amount of substrate required. More coarse grits with higher content of stone particles are used to remove thick layers of grime and oil from stone surfaces. A coarse grit will also leave an authentic aged effect on older stone once cleaned. A finer media would give an uncharacteristic effect to the stone and probably remove any charm and aesthetic value of old walling. A finer grit would normally be employed for use upon surfaces with a special finish such as stainless steel or aluminium.
  • Calcium Carbonate is normally used at low pressure to remove grime from delicate surfaces such as fabric or wood. Interior beams that needed revitalising, for example, could be treated in this way. Any work that is to be carried out inside will not be a small operation owing to the clean up costs and so it may be advisable to carry this out when other decoration work is taking place. Ask the company about the best order to carry out work as doing things in the wrong order could lead to repeating tasks and increasing costs. The effectiveness can be increased at low pressures by using a vortex pressure system. The most common use is to strip paint from aluminium surfaces.
  • Dry ice is becoming an increasingly popular choice for blast cleaning owing to the fact that it evaporates and therefore the cleanup costs are massively reduced. Much of the effectiveness of using dry ice is down to the sudden cooling effect on the surface that can be used to separate a coat of resin from metal for example. The particles of dry ice expand as they sublime from solid to gas. This means that any cracks in the surface will be forced open by this action. Carbon dioxide is non-conductive and can be used without any risk of interference with electrical equipment or safety risk to the user.
  • Air or water – Non contact cleaning using air or water is not “blast cleaning” as such, but employs the same principle to remove debris or waste or to clean surfaces. Small air blowing guns can be very useful for intricate cleaning jobs such as removing mould from tiling grout in bathrooms.
  • Specialist – There are some more unusual substances that can be used for particular processes to create effects. Walnut shells are used for polishing and mould removal and are particularly effective because of their decarbonising action. Ferro silicon is a very aggressive choice and can also be used to harden surfaces or making them non slip as a residue of silicon remains on the surface.


Graffiti Removal

Graffiti is a criminal activity and is often seen as a symptom of urban decay and inner city crime. Although various councils are trying to legitimise it by providing legitimate areas and presenting it in a more positive light, no one is going to be impressed by a property that appears to have been vandalised.

Depending on the size of the piece that is to be removed and the paint used, it may be possible to completely remove any signs of it using grit blasting or pressure washing alone or in conjunction with some type of chemical treatment.


When building an extension directly onto a property that is more than ten years old, one of the most difficult tasks is matching the texture and colour of the new brickwork with that of the old. If done poorly the new building can look almost unsightly and even lower the value of the house. With very old stone that has been severely weathered and may have come from a unique source, this process of matching becomes even more difficult.

Grit blasting can be used very cleverly to create an artificially weathered or aged look to the new stone and when done in direct comparison to the original building, can mask the evidence that the property has recently been extended. The most successful results are achieved when the old brick is treated at the same time so that both surfaces can be brought to the same shade and hue.


Work on small items such as light fittings or metalwork can be done in blast cabinets. These contain the debris created by the cleaning and used more expensive media (such as glass bead, alumina or chilled iron) to blast the surface. A filtering system can be put in place to separate the particles so the blast media can be reused to reduce cost.

Such machines are extremely expensive pieces of equipment and require training and practice to achieve good results and so are not usually available for hire. A workshop will more commonly carry out the work for you.

Before embarking on a large cleaning job, it is worth exploring the alternatives (chemical methods etc) to ensure that this method is the most suitable. Small aluminium units can be hired, although without the correct training these are likely to cause more harm than good. They usually weigh around 15 kilograms without substrate and are worn on the back, so require a good level of physical strength for their operation.

Companies which hire equipment should be able to offer training and advice themselves or recommend a training company.

Interior work must be carried out with proper ventilation and ideally some sort of extractor fan to remove any circulating particles that may cause potential harm. Full face masks and protective clothing should be worn and the area should be assessed to ensure that it is in a safe and habitable state.

Some important questions to ask

Is a prior visit required before the work can be carried out?

A company that says no may not be entirely reliable. If it is a small job that can easily be described on the phone or by emailing a few pictures only one visit may be required, but larger jobs need to be properly assessed before they are undertaken.

The surface type, nature of material that is to be removed and extent of cleaning all need to be carefully assessed before work is undertaken and any company that is prepared to just turn up and have a go without the correct preparation are not likely to carry out work to the highest standard.

Issues of access and surrounding surfaces and conditions also need to be considered so the work can be carried out safely and in a contained manner and to carry out the associated risk assessment.

The available power sources also need to be looked at, as a source of compressed air will also be needed but this is unlikely to be available at most residential addresses. If the required power supply is not available a generator or converter may also need to be used. Are all employees competent at using the equipment?

It is very important that the people who you are paying to carry out any work are fully trained, and a good company will be able to provide training certificates or diplomas to prove this fact.

What is the company history and background?

Before parting with any deposit money you should have gained enough information about the company to be fully confident in the service you will require. Details about how long they have been in business, the location of the office or primary business address and the size and nature of the business are good pieces of information to acquire.

Some details regarding the size and type of previous work they have carried out is also very important. A good company should be able to provide details and pictures (a very good one may even show you the site and work itself) and references.

In addition, hire companies who you have not previously dealt with should ask you for several forms of identification and company letterhead in order to protect themselves. Failure to do this could be a sign of inexperience or unprofessional manner. Either way they may not be the best people to entrust a large job or sum of money to.

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