Wet blasting — the finish dry blasting cannot give

In a wet blasting cabinet — vapour blasting in English — water and blasting media sit mixed as a slurry in the cabinet sump. A pump lifts the slurry to the gun, compressed air joins it at the nozzle, and the stream hits the part. Everything drains back into the sump and is used again — a closed loop, with a sedimentation filter pulling out broken-down media and loosened dirt along the way.

The decisive word is water. In dry blasting every grain strikes at full speed and hits into the surface. In the slurry each grain is wrapped in water that lubricates and cushions, so the stream cleans along the surface instead. The method grew out of the jet-engine world of the 1940s, and the principle is unchanged today.

Satin, as-new finish. Because the stream cleans along the surface, it evens the surface out rather than roughening it. Aluminium comes out looking the way it left the foundry — this is what restorers mean when they say parts look new, not freshly blasted.

No embedded grains. In dry blasting, hard grains can lodge in soft metals and later ruin paint, bonding or bearings. The water film prevents it — and as a bonus the media lives longer, since the grains are not crushed as hard.

Zero dust. All dust is bound in the water. The method was originally developed precisely to remove the dust hazard of blasting — in the workshop that means cleaner air and a cleaner shop.

Wet blasting is the gold standard where the part is worth more than the time: aluminium engine and gearbox castings, carburettors, cylinder heads, vintage parts, bicycle and motorcycle components, stainless details. Anything that should look new without losing dimensions or markings.

The typical media in the slurry is glass bead — the soft peening plus the water cushion is the combination behind the characteristic finish. Small parts go in a basket or drum; a turntable or a fixed gun holder makes even work easier on small pieces.

Degreasing — possible, but not recommended. Wet blasting can remove oil and grease as it polishes, and the part comes out clean. But do not use the cabinet as a degreaser: larger amounts of oil and grease in the water give unwanted results — an oil film on the glass and elsewhere inside the cabinet — and the life of the slurry can be cut dramatically. Degrease the parts before they go in.

Wet blasting does not replace dry blasting — it is the other half of the workshop. Heavy removal loses in water: thick paint, coarse rust and mill scale go clearly faster in a dry cabinet with a cutting media. The water that cushions the grains is exactly what makes them less aggressive.

The practical division: dry cabinet to remove, wet blasting to finish. A part with thick coating may visit both — stripped dry, polished wet. A part that is merely dirty and oxidised goes straight to wet.

Strip completely. Slurry finds its way in wherever water does. Bearings come out — not masked and hoped for; bearing seats, cylinder bores and gasket faces are shielded or kept out of the stream.

Rinse and blow out everything afterwards. Oil galleries, threaded holes and cavities are rinsed clean and blown dry — stray glass beads in an oil gallery can potentially mean enormous costs or a wrecked engine.

Protect against flash rust immediately. A freshly polished part is chemically clean, wet and completely unprotected — bare steel can start rusting within hours, and aluminium dulls down. Dry the part and apply corrosion protection or oil as the job's final step, not as tomorrow's reminder.

Maintain the slurry. The media concentration in the water is one of the most important settings — a thin slurry cleans slowly, and worn-out media gives a dull, uneven result. Follow the machine's instructions for mix ratio and replacement, and empty the sedimentation regularly.