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There is sometimes confusion over the terms
VOC of coating and
VOC of material. The VOC of coating is the same as the
term “regulatory VOC”, which is equivalent to the term "VOC, less water and
exempts". The VOC of material is the same as the term "actual VOC ", which
is equivalent to the term "VOC, including water and exempts".
| The VOC of coating calculates the VOC less exempts and water, which is a
more complicated calculation than the VOC of material, in that it subtracts
the volume of water and the volume of exempt compounds
from
the volume of material, in the denominator. The calculation was derived to express the VOC emitted per
volume of coating solids to eliminate the effect of dilution. Dilution with
water or exempt solvents would reduce the VOC-to-paint-volume ratio while
maintaining a constant VOC-to-paint-solids ratio. This is important because
coatings are applied at a certain film thickness so dilution would result in
a larger volume of the coating being applied to achieve the same film thickness. |
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For conventional solvent based coatings with no exempt compounds, the two
values are always the same. For waterborne coatings and coatings containing
exempt compounds, the VOC of coating is always the higher of the two values.
The VOC limits listed in the Table of Standards refer to the VOC of coating.
The only exception is for low solids coatings where the purpose of the
coating is not to build film thickness.
Low solids coatings, which are
defined as coatings containing less than one pound of solids per gallon of
coating, are regulated by the VOC of material. VOC emissions, including the
emissions fee in Rule 314, are also calculated based on the VOC of material.
The link below is
to a spreadsheet that will calculate the both
VOC values based on the solids, water content
and density of the coating.
VOC
Calculator (xls-90k)
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