ASTM D6386-99
(Practice)Standard Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting
Standard Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting
SCOPE
1.1 This practice describes methods of preparing surfaces of new and weathered hot-dip galvanized steel for painting. Hot-dip galvanized steel is produced by the immersion of fabricated or unfabricated products in a bath of molten zinc, as specified in Specifications A 123 or A153/A153M. This practice covers surface preparation on iron and steel products and hardware that have not been painted previously. Galvanized surfaces may have been treated with protective coatings to prevent the occurrence of wet storage stain. This practice does not apply to sheet galvanized steel products nor to the coil coating or continuous roller coating processes.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D6386–99
Standard Practice for
Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and
Steel Product and Hardware Surfaces for Painting
This standard is issued under the fixed designation D 6386; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 Society for Protective Coatings Specifications:
Surface Preparation Specification No. 1 Solvent Cleaning
1.1 This practice describes methods of preparing surfaces of
Surface Preparation Specification No. 2 Hand Tool Clean-
new and weathered hot-dip galvanized steel for painting.
ing
Hot-dip galvanized steel is produced by the immersion of
Surface Preparation Specification No. 3 Power Tool Clean-
fabricated or unfabricated products in a bath of molten zinc, as
ing
specified in Specifications A 123 or A 153/A 153M. This
Surface Preparation Specification No. 7 Brush-Off Blast
practice covers surface preparation on iron and steel products
Cleaning
and hardware that have not been painted previously. Galva-
Paint Specification No. 27 Basic Zinc Chromate-Vinyl
nized surfaces may have been treated with protective coatings
Butyral Wash Primer
to prevent the occurrence of wet storage stain. This practice
doesnotapplytosheetgalvanizedsteelproductsnortothecoil
3. Summary of Practice
coating or continuous roller coating processes.
3.1 This practice describes the preparation methods that
1.2 The values stated in SI units are to be regarded as the
provide clean and suitable galvanized surfaces for painting,
standard. The values given in parentheses are for information
specifically so that an applied coating system can develop the
only.
adhesion necessary for a satisfactory service life.
1.3 This standard does not purport to address all of the
3.2 The zinc coating is constantly in a state of change. From
safety concerns, if any, associated with its use. It is the
the time the steel part is removed from the galvanizing kettle,
responsibility of the user of this standard to establish appro-
the exposed zinc coating interacts with the environment to
priate safety and health practices and to determine the
form, first zinc oxides, next zinc hydroxides, and then zinc
application of regulatory limitations prior to use.
carbonates. The process of complete conversion of the outer
2. Referenced Documents layer of zinc carbonates can take up to two years of exposure
to the environment, depending on the local climatological
2.1 ASTM Standards:
conditions. During the first stage, known as newly galvanized
A 123 Specification for Zinc (Hot-Dip Galvanized) Coat-
steel, the exposed surface consists mainly of zinc metal with a
ings on Iron and Steel Products
small amount of zinc oxide. During the second stage, known as
A 153/A 153M Specification for Zinc Coating (Hot-Dip) on
partially weathered galvanized steel, the exposed surface
Iron and Steel Hardware
consists mainly of zinc oxides and zinc hydroxides with some
A 780 Practice for Repair of Damaged and UncoatedAreas
zinc carbonates. At the final stage, known as weathered
of Hot-Dip Galvanized Coatings
galvanized steel, the exposed surface consists mainly of
B 201 Practice for Testing Chromate Coatings on Zinc and
water-insoluble zinc carbonates, some zinc oxides, and rarely,
Cadmium Surfaces
zinc hydroxides. The surface preparation for each of these
E 376 Practice for Measuring Coating Thickness by
stages must be treated separately.
Magnetic-Field or Eddy-Current (Electromagnetic) Test
3.3 Variationsinsurfacepreparationproduceendconditions
Methods
that differ, hence they do not necessarily yield identical results
when paints are subsequently applied. Service conditions will
This practice is under the jurisdiction ofASTM Committee D-01 on Paint and
Related Coatings, Materials, and Applications, and is the direct responsibility of
Subcommittee D01.46 on Industrial Protective Clothing. Available from the Society for Protective Coatings, 40 24th St., 6th Floor,
Current edition approved Feb. 10, 1999. Published April 1999. Pittsburgh, PA 15222–4623.
2 6
Annual Book of ASTM Standards, Vol 01.06. This interaction is described in “Duplex Systems,” van Eijnsbergen, J.F.H.,
Annual Book of ASTM Standards, Vol 02.05. Elsevier Science, New York, NY 1994, and in Zinc Handbook, Porter, F., Marcel
Annual Book of ASTM Standards, Vol 03.03. Dekker, Inc., New York, NY 1991.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6386
dictate the type of surface preparation to be selected, although thereof. This solution can be applied through immersion in a
the quality produced by any individual process may vary with tank filled with the solution, sprayed, or brushed with a soft
different compositions of the zinc surface. bristle brush, usually nylon and not steel or copper. When
dipping or spraying, the solution works best in the temperature
4. Significance and Use
range from 60 to 85°C.After cleaning, rinse thoroughly in hot
4.1 This practice describes the procedures that can be used water or water under pressure.Allow to dry completely before
proceeding. Whenever galvanized steel is rinsed, it is desirable
to prepare new and weathered zinc-coated surfaces on after-
fabricationsteelproductsforpainting,andthatcanimprovethe to use heated drying to accelerate the complete removal of
water from the surface.
bond of paint to the zinc surface.
5.3.2 Solvent Cleaning—Typical cleaning solvents, such as
5. Processes for Newly Galvanized Steel
mineral spirits or high-flash naphtha, can be used to remove oil
5.1 Newly Galvanized Steel—The category of newly galva- and grease. The procedure to be used is as specified in SSPC
nized steel refers to zinc-coated steel that has no surface Surface Preparation Specification 1. Proper rags or brushes
treatment after galvanizing, such as water quenching or chro-
should be used to wipe the galvanized parts.
mate conversion coating, and has been galvanized within the
NOTE 1—Caution: Theseragsorbrushesshouldbecleanedorrecycled
previous 48 h. There also should be no visible signs of zinc
often since oil can accumulate on their surfaces and be transferred back to
oxide or zinc hydroxide, which first appear as a fine white
the galvanized part. Small parts may be dipped or cleaned in ultrasonic
powder.
baths of solvents. After cleaning, rinse thoroughly in hot water or water
5.2 Surface Smoothing—Hot-dip galvanized surfaces gen- under pressure. Allow to dry completely before proceeding.
erally are relatively smooth after galvanizing. There may be
5.3.3 Hand or Power Tool Cleaning—Hand or power tool
some thick edges due to excess liquid zinc run-off during the
cleaningmaybeusedtocleanlightdepositsofzincreactionby
galvanizing, or high spots in the coating due to included
products, such as wet-storage stain, as specified in SSPC
iron-zinc intermetallics (dross) or zinc oxide particles. These
Surface Preparation Specification 2 or 3.
high spots and rough edges, such as the metal drip line, must
5.4 Surface Preparation—Hot-dip galvanized surfaces have
be smoothed to avoid paint film gaps in the areas of the high
a layer of zinc oxide and zinc hydroxide that must be removed
spots.
before paint will adhere to the zinc coating. Zinc coatings
5.2.1 Zinchighspots,thosethatwouldcausepaintfilmgaps
generally are relatively smooth and may be slightly roughened
suchasthemetaldripline,shouldberemovedbycleaningwith
prior to painting. The following four methods may be used to
hand or power tools as described in SSPC Surface Preparation
prepare the galvanized surface for painting.
Specification 2 or 3. The zinc should be removed until it is
5.4.1 Sweep Blasting—Abrasive sweep or brush blasting,
level with the surrounding area, taking care that the base
which uses a rapid nozzle movement will roughen the galva-
coating is not removed by the cleaning methods. After clean-
nized surface profile. The abrasive material must be chosen
ing, the surface shall be inspected for conformance to the
withcaretoprovideastrippingactionwithoutremovingexcess
required zinc thickness in accordance with Specifications
zinc layers. One of the materials that has been used success-
A 123 or A 153/A 153M utilizing a magnetic thickness instru-
fully is aluminum/magnesium silicate. Particle size should be
ment in accordance with Practice E 376. Any item falling
in the range of 200 to 500 µm (8 to 20 mils). Other materials
below the required zinc thickness, before or after removal of
that can be used are soft mineral sands with a Mhos hardness
any high spots, shall be repaired in accordance with Practice
of five or less, organic media, such as corn cobs or walnut
A 780.
shells, corundum, and limestone. Depending on the value of
5.3 Surface Cleaning—Hot-dipgalvanizedsurfacesmustbe
hardness for the abrasive medium, blasting pressure may need
clean and free of oil and grease before they are painted.
to be determined for the appropriate nozzle to work-piece
Adhesion problems have been experienced with newly galva-
distance, geometry of the component, and blasting medium.
nized articles that have been water quenched or treated with
For some all-alloy coatings, even the relatively low-pressure
chromate conversion coatings. These two post-galvanizing
blast of 0.15 to 0.25 MPa (20 to 40 psi) can be too great,
treatmentsarenotrecommendedforgalvanizedarticlesthatare
causing cohesion problems. Oil contamination of the com-
to be painted.
pressed air will degrade paint adhesion to sweep-blasted
5.3.1 Aqueous Alkaline Cleaning—An alkaline solution, pH
hot-dip galvanized surfaces. Care is needed in averting this
in the range of 11 to 12 definitely not greater than 13, can be
type of contamination. Care must be taken to leave zinc layers
used to remove traces of oil, grease, or dirt.An alkaline cleaner
intact. The purpose of sweep blasting is to deform, not remove
is unsuitable for removal of heavy build-up of zinc oxide or
the galvanized metal.Any area falling below the required zinc
wet storage stain (see American Galvanizers Publications, Wet
thickness, before or after sweep blasting, should be repaired in
Storage Stain , for description of these conditions). See 5.4 for
accordancewithPracticeA 780.Theprocedureforthisprocess
removal of zinc oxide layer. The alkaline solution nominally is
can be found in SSPC Surface Preparation Specification 7.
2 to 5 % sodium compounds, with small additions of emulsi-
Sweep blasting of zinc should be not less than 110 m /h (1200
fying, chelating, or sequestering agents, or a combination
ft /h) using these abrasive materials. The substrate should be
maintained at a temperature greater than 3°C (5°F) above the
dew point temperature. Following abrasive blast cleaning,
AvailablefromAmericanGalvanizersAssociation,12200E.IliffAve.,No.204,
Aurora, CO 80014–5376. surfaces should be blown down with clean, compressed air. In
D6386
some atmospheric conditions, such as high humidity, or high dust, dirt, oils, grease or deposits are present, they must be
temperature, or both, the formation of zinc oxide on the blasted removed with a mild alkaline degreasing solution (pH 11.5
surface will begin very quickly, so the paint coating should be max) followed by a thorough rinse with hot water (60°C
applied immediately, within 60 min, after sweep blasting. Zinc maximum temperature) or a pressure wash, then thoroughly
dried.This treatment is applied in the galvanizing plant or later
oxide formation is not visible to the naked eye; therefore, in
any atmosphere, painting should be stated as soon as possible in the paint shop. When applied in the paint shop, the surface
must first be appropriately cleaned as just described to remove
after surface preparation.
contaminants picked up after galvanizing.
5.4.2 Zinc-Phosphate Treatment—This conversion-coating
5.4.5 Notification of Surface Treatment—The paint shop
process consists of reacting the newly galvanized zinc surface
must be notified as to how the galvanized articles have been
in an acidic zinc phosphate solution containing oxidizing
processed and which surface treatment method, if any, is used
agents and other salts for accelerating the coating action. The
to prepare the surface.
zinc surface is converted to a crystalline phosphate coating of
the proper texture to inhibit corrosion and increase the adher-
6. Processes for Partially Weathered Galvanized Steel
ence and durability of the paint film. This process may be
6.1 Before preparing the surface of partially weathered
applied by immersion, spray or soft bristle brush application.
galvanized steel, the surface must be checked for the presence
After a time period of 3 to 6 min, the surface should be washed
of chromate conversion coating. The presence of a chromate
with clean water and allowed to completely dry before appli-
conversion coating can severely impair the adhesion of some
cation of the paint system. Painting should take place soon
paint coating system. Chromate conversion coatings can be
after treatment to avoid pick up of surface contaminants.
applied at the galvanizing facility to protect the newly galva-
5.4.3 Wash Primer Treatment—This process involves the
nized surface from excessive growth of zinc oxide and zinc
use of a metal conditioner to neutralize surface oxides and
hydroxide,commonlycalledwetstoragestain.Thepresenceof
hydroxides along with etching the surface. One example of a
chromateconversioncoatingscanbedetectedbytheprocedure
wash primer is SSPC Paint Specification 27. The process is
outlined in Appendix X1. The removal of the chromate
based on three primary components: a hydroxyl-containing
conversion coating also is outlines in Appendix X1. The
resin: a pigment capable of reacting with resin and acid: and,
surface preparation method described in 5.4.4 could test
an acid capable of making the resin insoluble by reacting with
positive for the presence of chrome. The surface preparation
the resin, the pigment, and the zinc surface. The result is a film
technique described in 5.4.4 should not be removed if it tests
of approximately 8 to 13 µm (0.3 to 0.5 mils). Failures can
positive for the presence of chrome. This process is not a
occur if the film exceeds 13 µm (0.5 mils). The film usually is
chromate conversion coating. If the galvanized surface has
applied by spray but may be applied by soft bristle brush, dip,
thick edges or high spots, these should be removed, see 5.2.1.
or roller coater. Using these latter coating methods, it may be
When the high spots
...
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