An Evaluation of MoDOT's Current Coatings Programs Final ... - TSP2

Hazardous Metals
The presence of lead or other toxic metals in paint can significantly increase the cost of
repairing an existing coating if special provisions for containment and worker protection
are required. A cost multiplier of 2 is typically used when lead or other hazardous
metals are present, although this multiplier can be adjusted. The presence of
hazardous metals in the paint is established based on discussions or research about
the structure history, through use of field Lead Check swabs, and/or through paint chip
sampling and laboratory analysis.
Phase 2 – Physical Tests of Coating Integrity
Physical tests of coating thickness and adhesion are generally made on structures
which are in the B or better condition. On these structures, overcoating may be an
option. These tests are necessary in order to determine whether the existing coating is
of sufficient integrity to be overcoated (i.e., whether it can support additional coats).
While this testing can be done anytime, on large projects, it is better to delay it until the
specific areas that will be overcoated are identified. In this way, the amount of
destructive testing is limited to those surfaces where it is applicable, and the testing is
current. For example, adhesion tests today on coatings that will not be overcoated for
two years are not relevant. To be accurate, the testing should be repeated at that time.
Further, MODOT may wish to overcoat certain surfaces for aesthetics only, rather than
to arrest corrosion. If those items exhibited only a limited amount of visible corrosion
during the initial survey, testing would not have been triggered.
When the testing is performed, coating thickness is measured using non-destructive,
magnetic dry film thickness gages calibrated on National Institute of Standards and
Technology (NIST) calibration plates. Typically, a PosiTector® 6000 is used. This
assessment provides the thickness of all coats combined.
Adhesion tests are conducted at random locations in accordance with Method A of
ASTM D3359, “Measuring Adhesion by Tape Test.” Method A requires scribing an “X”
through the coating with a sharp knife followed by the application and removal of a
pressure sensitive tape. The amount of coating removed in the test area is evaluated
using an ASTM rating scale. Ratings of 0A and 1A typically represent poor adhesion,
2A and 3A moderate adhesion, and 4A and 5A good adhesion.
Risk of Overcoating
The physical test results from the field investigation are factored into the decision
considerations to determine the risk of applying additional coats to the existing system.
The risks can be calculated and defined as follows:
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