How to blast softer substrates
Restoring fire-damaged wood, concrete and brick by hand is only cost-effective for small surface areas. Media blasting is so much more productive that it makes economic sense to tackle residential restorations and mould remediation projects with soda blasting and dry-ice blasting. In turn, these methods pale in comparison to abrasive blast cleaning in terms of productivity, but have the critical advantage of not damaging the underlying substrate. With dry blasting out of the question, how does the restoration professional efficiently clean vast surface areas – schools, hospitals, government facilities, or any large commercial or industrial building – without compounding the damage?
Blasting With Organic Materials
Organic material like ground corn cob and crushed nut shells are non-toxic and environmentally-friendly soft media that are good for stripping paint and contamination from wood substrates. They produce a low amount of dust, but don’t cut as effectively as harder, more angular media and are relatively expensive, making them a less-than-ideal choice for large projects, especially when the media can’t be recycled.
Dry Ice Blasting
Dry ice leaves nothing to clean up except dislodged contaminants.
Dry ice is a go-to mould remediation method. The distinctive feature of dry ice is that it sublimates – passes from a solid to gaseous state – so it doesn’t leave spent abrasive for clean-up and removal. This is advantageous when working in attics or other tight spaces, especially if you are on your back, blasting overhead.
However, the fact that the media sublimates doesn’t mean that there no residue to clean up – whatever contaminant comes off the substrate still has to be swept up or vacuum cleaned afterwards, so the amount of material to dispose of is reduced but not eliminated, and doesn’t translate into significant savings of time or labour. In addition, using dry ice presents logistic challenges, especially on large projects: the media comes in large bins (500 lbs), suffers degrading productivity over time, and ultimately perishes.
Baking soda is a blast media widely used for fire damage restoration. Its angular shape gives it good cutting power for such a soft media (2.5 Mohs) and it deodorizes surfaces on contact. Baking soda is biodegradable, but it kills vegetation, so it requires containment when blasting outdoors. Indoors, soda produces a heavy dust which can cause visibility problems in enclosed spaces and necessitates full containment, negative air pressure and ventilation, especially when dealing with mould, where it is critical that dislodged spores don’t circulate to unaffected areas.
These drawbacks can be negated to a degree by suppressing the dust and knocking down airborne mould and soot with water. This can be accomplished by using a water injection nozzle or halo ring which introduces water to the air stream. The disadvantage to this approach is that copious amounts of water are required for significant dust suppression, resulting in a slurry that needs to be contained and disposed of.
Soda blasting is a great option when surface damage must be avoided.
Vapour cleaning removes contaminants at rates that rival sandblasting, using a fraction of the water and abrasive.
Vapour cleaning presents a middle way for soda blasting. In the vapour cleaning process, soda media and water are stored in a pressurised pot, then pushed into the air stream. Soda particles are encapsulated in a water jacket, but there is no excessive free water. When the particle pulverises on impact, fine particles that would normally become airborne are sequestered in the water jacket and end up on the floor, where they can be swept up or vacuum cleaned away. Soda vapour cleaning yields comparable results to dry soda blasting, while drastically reducing dust.
For maximum productivity, nothing beats using a hard media. Organics, dry ice and soda just don’t have the same cutting power as crushed glass, glass bead or fine garnet. However, dry blasting equipment cannot blast effectively at pressures low enough to clean contaminants without damaging the substrate.
Unlike dry blasting, vapour cleaning can blast hard media at low pressures. Moistened media carries more mass, and when it strikes a surface, high-velocity water undercuts contaminants, prying and peeling them off the substrate. More force is delivered on impact but over a wider area, minimizing surface profile while delivering high production rates.
With glass bead, crushed glass and fine garnet, vapour cleaning at 25-55 psi is suitable for cleaning wood, brick, restoring monuments and other finished concrete surfaces, soft stone, and aluminium. At 56-90 psi, vapour cleaning is suitable for cleaning unfinished concrete.
The ultimate advantage of vapour cleaning is versatility. Next-generation vapour cleaning equipment like the Ecoquip 2 allows you to clean delicate substrates with soft abrasives at pressures as low as 25 psi, then switch to a coarse garnet or coal slag to blast heavily corroded and thickly coated steel to white metal blast cleaning at pressures up to 170 psi at the nozzle. No other tool enables you to meet such a wide range of restoration and surface preparation challenges.
Dispersing water jacket from a wet particle amplifies blasting effect.
Media blasting is the best way to efficiently clean large surface areas. When it is imperative to not damage the substrate, soft media like soda, dry ice and organic material are commonly used. The highest production rates are achieved with hard, fast cutting abrasives, which can be used effectively at low pressures without damaging the substrate with vapour cleaning equipment, which provides the added benefit of suppressing dust, which in turn substantially reduces containment and clean-up costs.