Abrasive Blasting: Striking the Balance Between Effectiveness and Erosion

Discovering Steam Abrasive Blasting and Cleaning

Renovating moulds and fire-damaged wood, concrete and brick using chemicals or steam is not always the lowest-cost method for managing damaged areas. Abrasive blasting can be highly efficient because it is generally more economical than restorations that require traditional soda blasting or dry ice blasting equipment. These methods lag behind abrasive blasting in terms of efficiency but offer an important advantage in not damaging the underlying structure. Dry abrasive blasting is often too dusty and sometimes too aggressive for certain renovation and improvement applications. How do renovation specialists effectively clean large surface areas such as schools, hospitals, public buildings or commercial or industrial structures without dry abrasive blasting and without causing further damage?

First, let us look at methods that will not work:

Organic abrasives such as ground corn cobs and crushed walnut shells are non-toxic and are suitable, environmentally friendly and soft abrasives for stripping paint and contamination from wood substrates. They produce minimal dust but their efficiency on large surface areas can be low. Dry ice is an important mould remediation method. The distinguishing characteristic of dry ice is its sublimation (transition from solid to gas state), so it leaves no abrasive material behind for cleaning and removal. This method is advantageous if you are working in attics or other confined spaces, particularly if you are spraying overhead and upwards. However, the sublimation of the abrasive does not mean there is no residue to clean - waste from the substrate must be swept or vacuumed. The amount of material to be disposed of is reduced but does not provide significant time or labour savings. In addition, logistical challenges arise, particularly on large projects when dry ice is used: the abrasive comes in large containers (200 kg), its efficiency decreases over time and eventually disappears. Inorganic abrasives such as glass beads, fine crushed glass or fine slag stone can be used in certain renovation applications. Glass beads are the softest of the three abrasives mentioned above. The three types of abrasive can be used for efflorescence removal, brick, stone or concrete cleaning and various types of renovation. The most important factors in deciding which abrasive to use are the spray pressure at the nozzle and the type, properties and age of the substrate being cleaned. Carbonate is a commonly used blasting abrasive in fire damage renovation.

Its angular shape provides good cutting power for such a soft abrasive (2.5 Mohs) and disinfects the surfaces it contacts. Carbonate is soluble in nature but kills vegetation; therefore dust containment is required during outdoor blasting operations.

Indoors, carbonate creates heavy dust that can cause visibility problems in confined spaces and requires complete dust containment, negative air pressure and ventilation, particularly when working with mould and loose spores must not spread to unaffected areas. These disadvantages can be mitigated to a certain extent by suppressing the dust and controlling airborne mould and isin with water. This can be accomplished by using a water spray nozzle or a halo ring that directs water into the air stream. The disadvantage of this approach is that large amounts of water are required to suppress significant amounts of dust and it creates a slurry that must be controlled and disposed of. Let us move on to methods that are likely to produce better results in areas with more damage, dust and dirt: Steam abrasive blasting or cleaning offers an alternative to carbonate blasting using less water. Steam abrasive blasting is a unique wet abrasive sprayer that uses a combination of abrasive, air and minimum water for maximum dust containment, compared to conventional wet abrasive blasting using less water.With steam abrasive blasting, the abrasive material and water are stored in a pressurised tank and then mixed into the air stream.

Abrasive particles are encapsulated in a water cell but there is no excessive free water. When particles are broken down into dust upon impact, the fine particles that would normally be dispersed into the air are trapped in the water cell and collected on the ground. The most important feature of steam abrasive blasting is the ability to use hard abrasives at low pressures. Moist abrasive carries more mass and when it strikes a surface, high-pressure water strikes waste from below, stripping and removing it from the layer.

More force is applied to a larger area and in addition to providing high production rates, minimises surface profile. Blasting with glass beads, crushed glass and fine slag stone at 1.7–3.7 bar pressure is suitable for wood, brick cleaning, monuments and other finished concrete, soft stone and aluminium surfaces. Steam abrasive blasting at 3.8–6 bar pressure is suitable for unfinished concrete cleaning or light surface preparation. The most important advantage of steam abrasive blasting is its versatility. New-generation equipment such as the Graco EcoQuip 2 steam abrasive blaster (steam abrasive) allows you to clean sensitive substrates with soft abrasives at pressures as low as 1.7 bar and then switch to thick slag stone or coal slag for white metal blasting cleaning of severely worn and heavily coated steel at pressures up to 11.7 bar at the nozzle. No other tool enables you to cope with such diverse renovation and surface preparation challenges.The new EcoQuip 2 Portable (EQp) is lightweight (99 kg) and can therefore be easily moved from one surface preparation job to another. Powerful enough for small and medium-sized jobs. It can spray up to 10.5 bar and can provide you with much of what a 10.5 m³/min compressor offers.

In addition, it is optimised to work well with a 5.2 m³/min compressor and can spray for up to 90 minutes between refills.

• Portability: It weighs only 99.8 kg and can be easily transported on a trolley with lifting handles. • Low water consumption (only 0.5–1 l/min) means less residue accumulation. • Works with thick, fine or non-destructive abrasives. • Fast removal rates compared to other cleaning methods: spray pressure up to 10.5 bar. • Sprays for up to 90 minutes between refills and holds approximately (4) 25 kg of abrasive. Steam abrasive blasting is the best way to effectively clean large surface areas. When damage to the surface is not permitted, soft abrasives such as soda, dry ice and organic materials are usually used. The highest production rates are achieved with steam abrasive blasting equipment using hard, fast-cutting abrasives that can be effectively used at low pressures without damaging the substrate, provide dust containment advantages and thereby reduce dust containment and cleaning costs.

EcoQuip 2 Application

Founded in 1924 as a ship engineering company, Malakoff Limited is today a leading engineering and manufacturing contractor located on the semi-arctic archipelago of Shetland Island within Scotland's borders. Based in Lerwick, Shetland, Malakoff provides comprehensive services for the oil and gas, auxiliary facilities and renewable products sectors. Malakoff recently carried out blasting and painting operations on the hull both above and below water for the whitefish trawler FV Devotion. This 22.85 metre long and 7.00 metre beam vessel was built from Scots pine on oak in 1993. The application of traditional sand blasting was not possible due to the wooden structural materials. However, thanks to the steam blasting process offered by EcoQuip 2, the entire hull was stripped back to bare wood without any damage. The Graco EcoQuip 2 steam blaster was purchased from Fluid Technologies Ltd at the end of 2016 and proved to add considerable value to Malakoff's blasting services. It enabled Malakoff to add a new service to its capabilities: Complete dirt removal from wooden-hulled vessels, a difficult and costly operation in its traditional form. The flexibility of the EcoQuip 2 also allowed it to be used for steel coating blasting on all final layers. Stephan Rindfleisch Product Marketing Manager AFTD Graco BVBA