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Decorative Finish | Sweep Blasting | Thicker Galvanized Coatings | Galvanized Steel in contact with Timber | Steel Detailing | Safe Buildings | Imported Steel Products | Advantages of After Fabrication Galvanizing | Standards Update | Materials Handling & Conveyors | Lintels and Shelf Angles | Zinc for Human Health | Atmospheric Corrosion Resistance | Paint over Galvanizing | Abrasion Resistance | Use of Galvanized Reinforcement | Repair of Field Welds | Wet Storage Stain | Distortion | Thickness on Flame-Cut Edges | Coastal Construction
Sweep Blasting
Hot Dip Galvanizing
Advisory Note
GEN/1/1
June 2001
This method of
surface preparation is appropriate before applying, good
top quality paint topcoats over galvanizing.
Particularly in
circumstances where good wet adhesion or semi immersion
of the combined system is intended light sweep blasting
can provide maximum topcoat adhesion over galvanizing.
To achieve a successful
result it must be understood that blast standards for preparing
steel are totally inappropriate for galvanizing where the
outer free zinc layer requires very little impact or scouring
action to promote adequate surface roughness.
The following
criteria should be observed.
- Blast pressure 40 p.s.i maximum
- Abrasive Grade 0.2 - 0.5mm (clean ilmenite)
- Angle of blasting to surface 45° angle
- Distance from surface 300-400 mm
- Nozzle type min 10mm of venturi type
These controls
will ensure that the severity of blasting does not damage
the galvanized surface and should remove only 10 µm
of surface zinc.
If operators with
good experience in sweep blasting are unavailable, it is
wise to begin with a greater distance between the nozzle
and the surface to be sweep blasted until standards for
the work have been established.
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