Vacuum Blasting

Vacuum blasting, also called closed-loop or dustless recovery blasting, is a form of abrasive blasting in which the nozzle is enclosed in a blast head with a brush or seal that rests against the surface. A vacuum draws spent abrasive, removed coating and dust back through a hose to a recovery unit, where reusable abrasive is separated and returned to the blast pot. Because emissions are captured at the point of work, vacuum blasting is used where open blasting would spread dust, lead or debris into occupied areas or sensitive environments.

How vacuum blasting works

A typical system has four parts:

1. Blast pot and compressor. Supply abrasive and compressed air, as in ordinary pressure blasting.
2. Blast head. A nozzle surrounded by a shroud with replaceable brushes or seals. Heads come in shapes for flat surfaces, inside and outside corners, pipe and beams.
3. Vacuum and recovery unit. A powerful vacuum draws material through a recovery hose to a separator.
4. Separation and dust collection. Cyclones and screens separate reusable abrasive from fines and debris. Fines go to a dust collector with filters.

The operator keeps the head in contact with the surface. If the seal is lifted or poorly matched to the surface shape, abrasive escapes.

Abrasives

Vacuum blasting usually uses recyclable abrasives that survive multiple passes:

• Steel grit and steel shot. Durable and recyclable many times. Grit gives an angular profile.
• Aluminum oxide. Hard and recyclable, useful on harder coatings and non-ferrous metals.
• Garnet. Sometimes used, with fewer recycles.

Expendable mineral abrasives are less suitable because they break down quickly. See abrasive media selection.

Where it is used

• Lead paint removal on bridges, buildings and industrial structures, where containment and worker protection are critical (see lead paint removal).
• Spot repair of coated steel in operating plants, refineries and power stations.
• Interiors of buildings, food plants and hospitals where open blasting dust is unacceptable.
• Concrete surface preparation in occupied areas, as an alternative to shot blasting concrete where machines cannot fit.
• Near sensitive equipment, such as electrical gear and rotating machinery.
• Ship and tank repair in limited areas.

Advantages

• Reduced dust and emissions at the point of work.
• Abrasive recovery, lowering waste volume.
• Less cleanup of spent abrasive from surrounding areas.
• Work near other trades with fewer disruptions.
• Lower containment requirements compared with open blasting in some situations. Containment is still evaluated per project; see blast containment.

Limitations

• Slower production. Coverage rates are much lower than open blasting because the head must stay sealed and the nozzle is small.
• Geometry. Complex shapes, bolts, edges and tight corners are hard to seal against. Some open blasting or power tool cleaning may still be needed.
• Visibility. The operator cannot see the surface under the head and must lift it to inspect progress.
• Equipment cost and maintenance. Recovery units, hoses and filters need regular service.
• Not truly dust-free. Some leakage occurs. Air monitoring and respiratory protection are still required where hazardous materials are present.

Surface quality

Vacuum blasting can achieve the same cleanliness grades as open blasting, such as SSPC-SP 10 / ISO Sa 2½ or SSPC-SP 5 / Sa 3, though at slower rates (see SSPC/NACE surface prep standards and ISO 8501-1 visual cleanliness grades). Profile depends on abrasive type and size. Measure it with replica tape or a profile gauge (see surface profile measurement).

Because the head captures dust, surfaces are often cleaner of loose dust than after open blasting, but dust contamination testing is still recommended before coating.

Safety considerations

• Assess hazardous materials in the existing coating before work begins, including lead, chromium and other metals.
• Use respiratory protection appropriate to measured exposures (see respiratory protection).
• Ground equipment to control static buildup in recovery hoses.
• Manage collected waste according to its classification (see coating waste disposal).
• Use dead-man controls at the nozzle, as with all pressure blasting.

Comparison with other low-emission methods

Key terms

• Recirculating blaster. A machine that blasts, recovers and cleans the abrasive in one closed loop.
• Blast head or nozzle shroud. The part that seals against the surface; heads are shaped for flat surfaces, corners and pipe.
• Reclaim separator. A cyclone or screen that separates reusable abrasive from dust and fines.
• Dust collector. The filter unit that captures fine dust before air is discharged.
• Steel grit. A recyclable abrasive commonly used in vacuum blasting because it survives many cycles (see abrasive media selection).

Frequently asked questions

Is vacuum blasting the same as wet “dustless” blasting?

No. Vacuum blasting captures dry abrasive by suction. Wet blasting uses water to suppress dust. Both are sometimes marketed as “dustless.”

Can vacuum blasting meet near-white blast?

Yes, with suitable abrasive and enough dwell time, though production is slower.

Do I still need containment?

Often some level of containment is still required, especially for lead removal. The project’s environmental and worker protection plan sets the requirement.

Related entries

• Abrasive blasting
• Blast containment
• Lead paint removal
• Abrasive media selection
• ISO 8501-1 visual cleanliness grades (new)
• Concrete surface profile (CSP) (new)