MIL-HDBK-1110
degree of cleanliness obtained in abrasive blasting depends on
the type of abrasive, the force with which the abrasive particles
hits the surface, and the dwell time.
6.7.1.1
Types of Abrasive Blasting
a) Air (Conventional). In conventional abrasive
blasting (Figure 1), dry abrasive is propelled against the
surface to be cleaned so that rust, contaminates, and old paint
are removed by the impact of the abrasive particles. The surface
must be cleaned of blasting residue before painting. This is
usually done by blowing clean air across the surfaces. Special
care must be taken to ensure that horizontal or other obstructed
areas are thoroughly cleaned. Uncontrolled abrasive blasting is
restricted in most locations because of environmental
regulations. Consult the local industrial hygiene or
environmental office for regulations governing local actions.
Procedures for containment of blasting debris are being used for
paint removal from industrial and other structures. The SSPC has
developed a guide (SSPC Guide 6I) for selecting containment
procedures depending upon the degree of containment desired. The
amount of debris generated can be reduced by recycling the
abrasive. Recycling systems separate the paint waste from the
abrasive.
b) Wet. Wet-abrasive blasting is used to control the
amount of airborne dust. There are two general types of wet
abrasive blasting. In one, water is injected near the nozzle
exit into the stream of abrasive (Figure 2). In the other, water
is added to the abrasive at the control unit upstream of the
nozzle and the mixture of air, water, and sand is propelled
through the hose to the nozzle. For both types of wet-blasting,
the water may contain a corrosion inhibitor. Inhibitors are
generally sodium, potassium, or ammonium nitrites, phosphates or
dichromates. Inhibitors must be chosen to be compatible with the
primer that will be used. After wet blasting, the surface must
be rinsed free of spent abrasive. (The rinse water should also
contain a rust inhibitor when the blasting water does.) Rinsing
can be a problem if the structure contains a large number of
ledges formed by upturned angles or horizontal girders since
water, abrasives, and debris tend to collect in these areas. The
surface must be completely dry before coating. When leaded paint
is present, the water and other debris must be contained and
disposed of properly. This waste may be classified as a
hazardous waste under Federal and local regulations, and must be
handled properly.
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