220
Fundamentals of Corrosion
has occurred to such a degree that undercutting, flaking, and delamination
of the substrate take place. As the small hole develops, the electrolyte has
access to the reverse side and corrosion now takes place on both sides of
the substrate.
7.5.6 Final Stage of Corrosion
Corrosion is now taking place at its most rapid and aggressive rate. Large
gaping holes are formed, causing severe structural damage.
7.6 Surface Preparation
Surface preparation, which includes cleaning and pretreatment, is the most
important step in any coating operation. For coatings to adhere, surfaces
must be free from oily soils, corrosion products, and loose particles. While
new wood surfaces may be coated without cleaning, old wood surfaces must
be cleaned to remove any loose, flaky coatings and oily soils. Chemicals are
used to remove mold release from plastics. Metals are cleaned using solvents, or aqueous chemicals, or by media blasting, sanding, and brushing.
The choice of cleaning method depends on the substrate and the size and
shape of the object.
To remove coating adhesion, pretreatments are applied after cleaning. In
the case of metals, these pretreatments also provide some corrosion resistance. Wood surfaces may require the priming of knots and the filling of
nail holes. Acids are used to remove loosely adhering contaminants and to
passivate cementitious and masonry surfaces. Some plastic surfaces may be
painted after cleaning to remove mold release, but others may require additional pretreatments to ensure coating adhesion.
A detailed discussion of the cleaning and pretreatment of various substances follows.
7.6.1 Metal Substrate Preparation
Initially, a “pre-surface-preparation inspection” should be made. This
inspection is to determine if additional work should be done by other
crafts before the start of surface preparation for painting. Such other work
might include grinding and rounding of edges and welds; removal of
weld spatter, heavy deposits of oil, grease, cement spatter, or other contaminants; moving equipment out of the work area; masking or otherwise
protecting equipment or items not to be painted in the work area; and
other such preliminary activities. Only after this is done can the painters
begin to work effectively.
Fundamentals of Corrosion
has occurred to such a degree that undercutting, flaking, and delamination
of the substrate take place. As the small hole develops, the electrolyte has
access to the reverse side and corrosion now takes place on both sides of
the substrate.
7.5.6 Final Stage of Corrosion
Corrosion is now taking place at its most rapid and aggressive rate. Large
gaping holes are formed, causing severe structural damage.
7.6 Surface Preparation
Surface preparation, which includes cleaning and pretreatment, is the most
important step in any coating operation. For coatings to adhere, surfaces
must be free from oily soils, corrosion products, and loose particles. While
new wood surfaces may be coated without cleaning, old wood surfaces must
be cleaned to remove any loose, flaky coatings and oily soils. Chemicals are
used to remove mold release from plastics. Metals are cleaned using solvents, or aqueous chemicals, or by media blasting, sanding, and brushing.
The choice of cleaning method depends on the substrate and the size and
shape of the object.
To remove coating adhesion, pretreatments are applied after cleaning. In
the case of metals, these pretreatments also provide some corrosion resistance. Wood surfaces may require the priming of knots and the filling of
nail holes. Acids are used to remove loosely adhering contaminants and to
passivate cementitious and masonry surfaces. Some plastic surfaces may be
painted after cleaning to remove mold release, but others may require additional pretreatments to ensure coating adhesion.
A detailed discussion of the cleaning and pretreatment of various substances follows.
7.6.1 Metal Substrate Preparation
Initially, a “pre-surface-preparation inspection” should be made. This
inspection is to determine if additional work should be done by other
crafts before the start of surface preparation for painting. Such other work
might include grinding and rounding of edges and welds; removal of
weld spatter, heavy deposits of oil, grease, cement spatter, or other contaminants; moving equipment out of the work area; masking or otherwise
protecting equipment or items not to be painted in the work area; and
other such preliminary activities. Only after this is done can the painters
begin to work effectively.