Paint
Coverage
Paint
coverage is determined by both the "Transfer
Efficiency" of the spray equipment and
the "Solids
Content by Volume" of the paint.
Transfer
Efficiency also varies with subjective issues
such as the painter or the way he adjusts the spray
equipment. Air movement or wind can also negatively
impact transfer efficiency.
The
attached chart outlines typical Transfer
Efficiency for generic equipment but it is best
to consult your spray equipment supplier for more precise
values. Paint "bounce back" from the work piece
and "over spray" account for the paint loss,
which as you can see from the table, is significant.
More importantly, there may be significant opportunity
to reduce your paint costs by improving the transfer
efficiency of your equipment.
Solids
Content by Volume is the volume of the nonvolatile
portion of a coating composition divided by the total
volume of the liquid coating, expressed as a percent.
Paint
with 35 % volume solids applied at 3 mils will dry to a film
of approx. 1.0 mil DFT (Dry Film Thickness). The shrinkage
is due primarily to the volatile solvents evaporating.
Adding
solvent to paint decreases the volume solids. Therefore,
higher wet film builds would be required to achieve the
same dry film thickness.
The
attached chart outlines the Theoretical
Coverage (sq.ft. per US gallon) of a paint for
various dry mil thickness at various solids content by
volume.
Paint
Coverage can also be strongly influenced by the
texture and porosity of the substrate. Theoretical
coverage assumes a reasonably smooth non-porous surface.
Anything else requires either more paint or a sealer
and only experience can determine the correct amount.
Lastly,
some paints and colors do not hide as well as others.
Increased film build and even additional coats of paint
may be required to achieve the true colour on a repeatable
basis.
Tristar
Coatings for the most part, uses an "in-house grind" of
powdered pigment in its formulations rather than adding
a colorant to a bulk produced tint base. In certain conditions,
this can reduce paint consumption by as much as 50 %
plus.
Determining
Quantity of Paint Required
(Sq. Ft. Coverage per U.S. Gallon)
A)
Calculate practical sq. ft. coverage per US gallon.
The Theoretical
Coverage table shows the sq. ft. coverage
per U.S. gallon at various total film builds (DFT).
Alternatively, most paint manufacturers will provide
the Theoretical Coverage at 1 mil DFT. That coverage
must be divided by the desired total dry film thickness
to be applied to obtain the theoretical coverage
at the desired mil thickness. For rough and/or porous
surfaces, the Theoretical Coverage must be reduced
accordingly.
Establish
the Transfer Efficiency of
Application Method
Practical
Coverage = Theoretical
Coverage X Transfer
Efficiency
B)
Calculate paint required
Determine
the sq. ft. area
U.S. Gallons required = (Area/Practical Coverage)+ 10 % for contingency.
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