Busting The Myths of
Wet Abrasive Blasting
Bill Eliason, Graco
Origins of Wet/ Vapor Abrasive Blasting
• Wet Abrasive Blasting was first introduced to counter
the dust created by dry blasting.
• Water usage in blasting was first tried in 1941
• Process was never perfected
• Negative perceptions exist
What Is Wet Abrasive Blasting?
– Water is mixed with abrasive and air and propelled by air
pressure
What Is Wet Abrasive Blasting?
– Abrasive is suspended in a water projected at high velocity by
a forceful flow of compressed air
Problems With Wet Blasting
• Each wet system… although eliminating dust has had
many drawbacks and problems
• Over time these drawbacks and problems from older
wet blast technologies have lead to many myths about
anything wet abrasive
Improving Wet / Vapor Blasting
• New developments in Wet and Vapor Abrasive Blast
technologies
– Increased production rates to decreased water consumption
– Optimized air, water and media ratio for optimal performance
– Able to achieve same profile compared to
traditional blasting methods
– Mixes water with media inside the pot
• Adds weight to each particle (weight X speed = momentum)
• Reduces friction which causes production to remain high
• Makes the transportation of the media more efficient because of
the lubrication factor
Busting or Confirming the Myths
• Myth # 1
– The New Wet and/or Vapor Abrasive Blast
Technology isn’t as fast as Dry Blasting
• Fact
– These new technologies are comparable to dry
abrasive productions rates, and in some cases
even faster
Myth Busting: Not as fast
Myth Busting: Not as fast
• That was over 40 mils (1.016 mm) of a thick lining at a
waste treatment plant – in real time.
• When timed and compared to dry blasting on this job
vapor abrasive blasting was 3 x faster
Myth Busting: Wet and Messy
• Myth # 2
– The New Wet and/or Vapor Abrasive Blast
Technology is too Wet and Messy
• Fact
– The new Vapor Abrasive Blast technology is using
far less water than older systems
• Uses 10 to 12 gallons an hour with 80 grit garnet
Myth Busting: Wet and Messy
Myth Busting: Won’t Meet Specs
• Myth # 3
– Using the New Wet and/or Vapor Abrasive Blast
Technology won’t meet SSPC SP10 specification
for near white metal
• Fact
– Does meet spec according to Joint Surface
Preparation Standard NACE No. 2/SSPC-SP 10
Near-White Metal Blast Cleaning
– Section 5: Blast Cleaning Methods and
Operation
– Sub Section 5.3
Myth Busting: Won’t Meet Specs
• Other methods of surface preparation (such as wet
abrasive blast cleaning) may be used to achieve a
near-white metal blast cleaned surface by mutual
agreement between those responsible for establishing
the requirements and those responsible for performing
the work. Information on the use of inhibitors to prevent
the formation of rust immediately after wet abrasive
blast cleaning is in Paragraph A5
Breaking The Myths
• Myth # 4
– The New Wet and/or Vapor Abrasive Blast
Technology won’t cut/remove hard coatings and
linings or pitted rust
• Fact
– Far more efficient at cutting hard coatings and
linings as well as mill scale and pitted rust because
of the way water and or vapor is utilized in the
system.
Breaking The Myths
Myth Busting: Steel Profile
• Myth # 5
– The New Wet and/or Vapor Abrasive Blast
Technology can’t achieve a deep profile on steel
substrates
• Fact
– These new wet technologies can achieve a full range
of profiles on carbon steel from .5 to 6.5 based on grit
size and hardness
Myth Busting: Steel Profile
• Additional advantages from Vapor and Wet Blast
technologies regarding profiles
– The profile has more peaks and valleys per cubic ft. creating better
coating adhesion
– This is possible because the technology uses smaller grit sizes due to
the additional weight (mass) added from water… creating the same
effect as if it was larger grit
Myth Busting: Steel Profile
• Dry Blast Systems use 16~20 grit to achieve deep
profiles
– 16 grit averages 0.043 inches (1.1mm)
– 20 grit averages 0.037 inches (0.94mm)
• Wet Abrasive Systems use 80~100 grit for a good
profile
– 80 grit averages 0.0065 inches (0.17mm)
– 100 grit averages 0.0048 inches (0.12mm)
• 100 grit is about 1/9 the size of 16 grit
Myth Busting: Steel Profile
• 9x more peaks and valleys in the same
area compared to dry blasting!!
• Giving greater coating or lining surface
adhesion
Understanding the Power of Water
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Why It Works
•
Momentum = Mass x Velocity
•
Water weighs 8.33 lbs. / gallon
•
By encapsulating each particle, you are adding from 60 to 120 lbs. to the weight of
the media per hour.
– Conventional blasters only have the weight of the media. Therefore, they try
to blast with larger particles in order to blast more aggressively.
•
Water assists flow of media through the blast hose, thereby reducing any loss of
speed caused by friction (drag). This keeps the momentum factor high.
•
Water acts to reduce splash-back by trapping the dust caused by both the media
and the coating being removed.
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Water Encapsulated Media
• Due to water’s surface tension, the media is encapsulated, which
adds weight and “lubricates” each particle.
• The added weight increases momentum. The lubrication is one of
the reasons why EQ’s hoses and nozzles last 3 to 5 times longer
than dry-blasting hoses and nozzles.
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Media and Water at Point of Impact
• When the encapsulated particle hits the surface, the “water-jacket”
is shed.
• This action traps any dust created by the media and the removed
surface material.
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The Hydraulic Effect
• The inertia of the water drives the droplet into the impact area,
and the force of the particle hitting the area is made far more
effective by this hydraulic reaction.
• Water cannot be compressed and will erupt out of the impact
area, causing additional removal of the coating being blasted.
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The “Feathered” Impact Zone
• The hydraulic reaction greatly improves efficiency (less media and
time required to do the same job).
• This aids in producing a “feathered” edge with the desired profile
to meet many different types of applications.
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Questions?
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