A Commentary On Paint Specifications

A Commentary On Paint Specifications

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SSPC-Paint COM November 1, 2004 – SSPC: The Society for Protective Coatings

1. Description
Since 1955, the SSPC has issued specifications for coat­ings that have performed well in actual use on steel structures. When these paint specifications are used in conjunction with the SSPC standards for surface preparation, paint application, and thickness measurement, they provide complete paint systems for most steel structures and environments. Tables 1 and 2 summarize the SSPC paint specifications. Each paint specification contains a scope and a description of the paint. The composition specifications also contain directions for use. Performance specifications provide wide latitude on composi­tion but require minimum performance levels that the coating must meet.

2. Approaches to Procuring Paint
Procurement of paint by specification represents an attempt by the purchaser to exercise a degree of control over the quality of the product. That degree of control may range from tight, as when one of the SSPC paints with composition specification is cited, to virtually nil, as when a minimally de­scriptive, generic designation is used, e.g., a zinc-rich primer, a shop coat, a urethane. In addition to purchaser control, specifications make competitive procurement practical.

Another approach to the purchase of paint is represented by the naming of a specific proprietary product, the composi­tion of which may be described in a label analysis. Usually, the citation of a proprietary product denotes a high degree of confidence in that product’s performance record. It also implies confidence in the manufacturer’s reputation for quality and integrity – in other words, in the likelihood that the manufacturer will continue to maintain the quality for which the product has become known.

Unfortunately, in a vain attempt to promote competition, faith in the performance expected of a known proprietary product is often undermined by addition of the bland phrase “or equal.” Adding an “or equal” provision to a procurement specification without specifying the criteria that characterize equality of performance is a meaningless exercise.

Composition specifications offer the assurance of a desired measure of quality, but they also have the disadvantage of “locking in” a product to the level of quality or value prevailing during a specific period in the history of an evolving technol­ogy. One of the important objectives of SSPC is to focus on the expertise of its highly qualified, voluntary collaborators on critical evaluations of the products of new technology, so that those products may be assimilated into the spectrum of reliable materials with deliberate speed.

While no organization deliberating by consensus can operate at a rapid pace, the background of information gen­erated by a mature organization such as SSPC presents the user with enough choices of time-tested paints, both old and new, to justify deferral of judgment on commercial products that are not as yet backed by documented history of proven performance in the field.

If a paint is procured through a pure composition specifi­cation, SSPC-Paint 16 for example, the purchaser knows the physical, chemical, and performance properties of the product. The manufacturer follows the formula to produce the paint.

If paints are not being supplied to a composition specifica­tion, the purchaser is entitled, without transgressing into the area of proprietary information, to request a statement of the product’s principal composition and performance parameters, such as the following:

  • Case histories of field performance
  • Performance in standard salt fog, combination cyclic salt fog/UV condensation tests, and condensing cabinet tests
  • Non-volatile content by weight and volume
  • Volatile organic compound (VOC) content
  • Viscosity range at a specified temperature
  • Viscosity reduction resulting from specifi cation dilution ratios with thinners
  • Spreading rate for complete hiding
  • Specific resistance properties where resistance to unusual chemical exposures is required
  • Special or unusual drying time requirements
  • Suitability for one or another type of application, such as brushing, airless spray, etc.
  • Lightfastness rating of the color pigments
  • Chalk resistance and gloss retention rating (for top­coats) under specified conditions of test at named exposure locations for indicated periods of time

While not all of these criteria may be important in specific circumstances, they are indicative of the kind of questions that any discriminating purchaser is entitled to ask any manufacturer who is supplying paint for exterior exposure.If purchasers believe that there are no specification paints available that exactly fit requirements, or if they feels that they would like to have a better paint than can be obtained from among the available specification paints, they may engage qualified professional consultanta to secure informed and objective guidance.

3. Current SSPC Specification Trends
3.1 COMPOSITION AND PERFORMANCE: In many of the current SSPC specifications, an attempt is made to combine the advantage of composition requirements, perfor­mance criteria, and availability from proprietary sources.

TABLE 1 SSPC PAINTS

PRIMER

DESCRIPTION

PIGMENT

APPROX. Wt. % PIGMENT

VEHICLE SOLIDS

APPROX. SET TO TOUCH (h)

DRY THROUGH (h)

MINIMUM SURFACE PREP. RECOMMENDED

% VOLUME SOLIDS

SSPC- Paint 8

A vinyl-aluminum primer; may be used over bare steel, or wash primer, or over other vinyls. Suitable for very severe neutral exposures and immersion.

Aluminum 100%

6.7

Vinyl

0.25

1

Near-white blast or pickling

14

SSPC-Paint 9

Vinyl primer similar to above. Recommended for alkaline or acidic exposure.

Titanium dioxide 95% min., tint 5% max.

12

Vinyl

0.25

0.5

Near-white blast or pickling

17

SSPC-Paint 15

Fast-drying shop paints for temporary protection of steel joists; performance based.

Not specified

Not Specified

Hand cleaning

SSPC-Paint 16

Two-component coal tar epoxy self-priming paint for water immersion, chemical, and underground.

Magnesium silicate or iron oxide

31

Coal tar pitch and polyamide and epoxy resins

Commercial blast

75

SSPC- Paint 17

Chlorinated rubber inhibitive primer for non-submerged surfaces and most sub­merged surfaces.

Rust inhibitor 65%, extender 35%

29-49

Chlorinated rubber 66%, chlorinated plasticizer 34%

0.25

1

Commercial blast

32

SSPC- Paint 18

Chlorinated rubber intermediate paint (or topcoat) in white or tints.

Titanium dioxide 75%*, magnesium silicate 15%, mica 10%

16-30

Chlorinated rubber 75%, chlorinated plasticizer 25%

0.25

1

Commercial blast

35

SSPC- Paint 19

Chlorinated rubber topcoat in white or tints.

Various

18-28

Chlorinated rubber 72% chlorinated plasticizer 28%

0.25

1

Commercial blast

35

SSPC-Paint 20 Type I Type II

Inorganic zinc-rich primer Organic zinc-rich primer

Zn Level 1 ≥85% Zn Level 2 77 to 85% Zn Level 3 65 to 77%

Varies

Not Specified

Commercial blast

SSPC-Paint 21 Type I high gloss Type II med. gloss

Highly weather resistant white or colored silicone-alkyd paint suitable for finish coat.

Various

Type I, 11-37 Type II, 29-48

Silicone alkyd

2

8

Commercial blast

60-67

SSPC-Paint 22**

Primer–Two-component polyamide epoxy primer for industrial exposure marine environment and some chemical exposure.

Red iron oxide, magnesium oxide, mica

46

Epoxy/poly­amide 65/35

2

8

Commercial blast

65

Intermediate–Two-com­ponent polyamide epoxy intermediate coat.

Red iron oxide, magnesium oxide, mica

40

Epoxy/poly­amide 65/35

2

8

Commercial blast

65

Topcoat–Two-component polyamide epoxy topcoat.

Titanium dioxide, chromium oxide, magnesium silicate, mica, lampblack

36

Epoxy/poly­amide 65/35

2

8

Commercial blast

60

SSPC- Paint 23

Air drying latex primer and intermediate coat for blast cleaned steel.

Not Specified

Not Specifi ed

Latex

4

24

Commercial blast

36

SSPC Paint 24

Air drying semi-gloss latex topcoat.

Not Specified

Not Specifi ed

Latex

4

24

Commercial blast

27

SSPC-Paint 25 Zinc oxide oil and alkyd primer for Zinc oxide Type I, 52 50/50 raw 20 36 Hand cleaning Type I, 65 hand cleaned steel. (French process), Type II, 54 linseed Type II, 70 Type I Type II has lower VOC content than red iron oxide, oil/long oil Type II Type I. magnesium alkyd silicate, mica

SSPC-Paint 25 Zinc oxide oil and alkyd primer for Zinc oxide Type I, 52 Type I, 34/66 6 18 Commercial blast Type I, 82 BCS blast cleaned steel. (French process), Type II, 54 raw linseed Type II, 86 Type I Type II has lower VOC content than red iron oxide, oil/alkyd; Type II Type I. magnesium Type II, silicate, mica 33/67 raw linseed oil/alkyd

SSPC-Paint 26 Very slow drying black one-coat Zinc oxide (French 54 80/20 raw 24 168 Hand cleaning 87 maintenance primer process) 16%, linseed basic lanolate 4%, oil/long oil magnesium silicate alkyd 75%, lampblack 5% SSPC Paint Wash primer for clean steel free of Basic zinc chro-— Vinyl butyral 0.5 4 Commercial blast 10 27*** rust and scale or for clean galva-mate nized metal.

SSPC-Paint 28 Water-borne epoxy primer for steel Not specified — — — — — — surfaces.

SSPC Paint 29 Zinc dust sacrificial primer, Min. 65% zinc in — — — — — — performance-based. dry film

SSPC-Paint 30 Weld-through inorganic zinc primer Zinc dust min. 65% — Water or — — — —

by wt of total solids solvent-reducible, self-curing

SSPC- Paint 31 Single-package, water-borne alkyd — — Ambient dry-8 24 — — primer, performance-based. ing, single-package

SSPC-Paint 32 Coal-tar emulsion coating. — — — — — — 40

SSPC-Paint 33 Coal-tar mastic, cold applied. — — — — — — 70

SSPC-Paint 34 Water-borne epoxy topcoat. Not specified — — — — — —

SSPC-Paint 35 Zinc oxide and medium oil alkyd Zinc oxide (French Type I, 41 Medium oil 7 (air dry) 18 (air dry) Commercial blast Type I, 37 primer for blast cleaned steel (air dry process), red iron Type II, 55 alkyd 0.75 (bake) Type II, 66 or low bake). oxide, magnesium Type I Type II has lower VOC content than silicate, mica Type II Type I.

SPPC- Paint 36 Two-component weatherable — — Min. 17% — — — — aliphatic polyurethane topcoat, polyisocya­performance-based nate by wt.

SSPC-Paint 37 Water-borne epoxy coating for — — Epoxy resin — — concrete — cementitious substrates, with curing performance based agent min. 40% by weight of total solids

SSPC-Paint 38 Single-component moisture-cure — — Polyisocya-— — — — weatherable aliphatic polyurethane nate product topcoat, performance-based that cures through a reaction with atmospheric moisture

SSPC-Paint 39 Two-component aliphatic polyurea — — Hindered, 30 min to — — — topcoat, fast or moderate drying, non-2 h performance-based hindered, or hybrid aliphatic polyurea

*These pigment compositions are from a control formula. **These pigments listed are for use in reference (or control) paint. A lead- and chromate-free pigment may be used provided it meets performance requirements. ***These paints include chromate-containing pigments. Users are urged to follow all health, safety, and environmental requirements in applying, handling, or disposing of these materials. Note: Alkyd and vinyl topcoats are summarized in Table 2.

TABLE 2

SSPC ALKYD AND VINYL INTERMEDIATE AND FINISH PAINTS

FINISH PAINT

PIGMENT

APPROX. Wt. % PIGMENT

VEHICLE SOLIDS

DENSITY (lb/gal)

DENSITY (kg/L)

APPROX. SET TO TOUCH (h)

APPROX DRY TO TOUCH (h)

REMARKS

SSPC-Paint 101 Type I, Leafing Type II, Non-Leafing

Aluminum 100%

13.3

Alkyd varnish (long oil)

8.4

1.0

4

10

For atmospheric use. Used as aluminum top coat over oil paints or alkyds. Used as barrier coat on bitu­mens. Type I is usually supplied ready to mix. Type II is supplied ready-mixed.

SSPC-Paint 102

Carbon black 100%

5.5

Alkyd varnish (long oil)

7.7

0.9

6

18

Very durable black finish coat for oil or alkyd paints. For atmospheric exposure, particularly severe industrial or railroad.

SSPC-Paint 104 Type I, White

Titanium dioxide 67%, extender 33%

47.5

Alkyd varnish (long oil)

11.6

1.4

6

18

White, inert pigmented, alkyd finish paint for use over oil or alkyd paints.

Type II, Medium to Light Gray or Tan

Titanium dioxide 26%, extender, tint 74%

42.4

Alkyd varnish (long oil)

10.7

1.3

6

18

Color to be specified. For use over oil or alkyd paint. Colorfast.

Type III, Light or Gray Green

Titanium dioxide 25%, extender, tint 75%

44.8

Alkyd varnish (long oil)

11.6

1.4

6

18

Color to be specified. For use over oil or alkyd paint. Colorfastness good, but depends upon tinting pigments used.

Type IV, Dark or Forest Green

Chrome green 90%, extender, tint 10%

21.5

Alkyd varnish (long oil)

9.0

1.1

6

18

Very dark chrome green alkyd paint. Colorfast­ness good in mild atmospheres, but poor in chemical exposure.

SSPC-Paint 106

Carbon black 100%

1

7.4

0.9

0.25

0.5

Black vinyl finish paint. Use over vinyls only or over wash primers. Very good resistance to most exposures.

SSPC-Paint 108

Aluminum paste

17

Thixo­tropic alkyd

4

16

High-build thixotropic aluminum leafing paint, 49% volume solids.

For two reasons there is still a need for some compositional requirements in most paint or coating specifications. First, the correlation between long-term durability and short-term accel­erated performance tests is still an incomplete one, in spite of considerable recent progress. Secondly, in the present state of the art, it is still essential for the buyer to know, for example, that a zinc-rich paint contains at least some zinc, and that an epoxy contains some epoxy.

3.2 PERFORMANCE LEVELS: Several specifications, (e.g., SSPC-Paint 34, a waterborne epoxy; SSPC-Paint 29, a zinc dust primer; and SSPC-Paint 39, a polyurea topcoat) have incorporated the concept of performance levels of paints. The higher the level, the higher the degree of confidence in the performance of the paint. Under this approach, a lower level is generally based on accelerated tests, which can be performed relatively rapidly, but which offer a lower degree of confidence. The second or third levels of performance may be based on actual exterior exposure of 12 to 48 months at defined exterior sites or may be based on longer term acceler­ated tests. In some instances, a low level may be used as an interim qualification. In this case, the specifier would accept the products for limited use while waiting to accumulate the longer time field data required for the higher level of performance.

3.3 VOC LEVELS: In response to the continuing aware­ness of protecting the environment, governmental districts now restrict the emission of volatile organic compounds (VOC) from painting operations. SSPC does not defi ne VOC levels because of the wide variation in VOC limits among different localities and among different applications. The contracting parties are referred to the federal, state, and local regulatory authorities for guidance on the allowable levels of VOC emissions.

4. Government Specifications and Standards
There are fewer federal and military specifications for paint and coating materials than in the past. Although both purely compositional and purely performance specifications exist, the majority of government specifications contain both compositional and performance requirements.

In order to speed the procurement process, some gov­ernment agencies maintain a qualified products list (QPL) of approved suppliers for approved formulations. Qualification requires complete compliance with every requirement within the specification, some of which may include months or even years of exposure testing. The paint may require both laboratory and exposure testing for conformance to specification require­ments. The fact that a product has been examined, tested, and placed upon a QPL by the preparer of the specification signifies only that at the time of inspection and test the manufacturer could make a product that met all specifi cation requirements. It in no way relieves the supplier from the obligation to deliver items meeting all requirements.

There is a federal regulation requiring compliance with a mandate from Congress to make greater use of commercial industry standards whenever they will meet the needs of the government because of availability and cost considerations. These standards are described as rules, conditions, or require­ments established by commercial standards-setting bodies concerning definition of terms; classification of components; specification of materials, performance, or operations; delin­eation of procedures; or measurement of quantity and quality in describing materials, products, systems, services, or prac­tices.

There are standard procedures for preparation, updating, and cancellation of federal and military specifications as the need arises. The user is responsible for preparing a specifica­tion. The Materials and Mechanics Research Center, which lists all projects in the Federal Standardization Class 8010 for the Department of Defense, establishes projects for each user requesting a project number.

Titles of specifications for paint materials use one key noun (e.g., coating, paint, enamel, compound, etc.) followed by descriptive adjectives (e.g., textured, vinyl, anti-corrosive, etc.). The federal code system for specifi cations for paint and coating materials usually starts with TT-, followed by the first letter of the type of material (e.g., E for enamel; P for paint, C for coating; etc.) and a number. A letter, starting with A, is added after the number as modifications are made. Thus, TT-P-28G, Paint, Aluminum, Heat Resisting (1200°F), is the code and title of the seventh revision of a specification for a paint used in hot areas. Specifications for similar materials are sometimes grouped together. Thus, TT-P-300 to TT-P-500 are reserved for pigments. Many of the pigment specifications that previously fell in this category have been replaced by ASTM specifi cations.

Most of the federal specifi cations were developed based on commercially available products with a high level of perfor­mance. The specifications usually consisted of a combination of performance and formulation requirements. As technology progressed, the raw materials used in commercially available products changed. This resulted in a virtual nonavailability of paints meeting the federal requirements in the marketplace. Manufacturers still had the ability to specially formulate batches of paint that would meet all specification requirements, but this was both costly and time consuming. As a result, in the mid to late 1990’s, most of the TT-P-xxx specifications were canceled and the government began making greater use of industry specifications. When no industry specification was available, replacement specifications, called Commercial Item Descriptions (recognized by the designation CID A-A­xxx), were developed using performance requirements to the greatest extent possible. Some of the old federal specification paints are still commercially available, but the government is no longer maintaining the specifications. Some of the DoD-P-xxx specifications are still active. A few discontinued specifi cations, such as MIL-P-15328, are available from SSPC.

In addition to specifications, there are federal tests (Federal Test Method Standard No. 141) and a few federal standards (e.g., Federal Standard No. 595 Colors) that are available from the Specification Distribution Branch of the GSA. A listing of all such specifications and a Federal Supply Classification listing can be found in the Index of Federal Specifications and Standards, available on a subscription from the Superintendent of Documents (or on the internet at http://assist.daps.dla.mil). Single copies of specifications for bidding can be obtained free from any GSA Business Service Center located in different cities.

Military specifications are distinct from other federal specifications. They are generally written with the prefix MIL- or DoD- (Department of Defense), followed by a code letter designating the type of product and a number assigned to each product. The DoD designation indicates all of the requirements of the specification are in metric. Many of the military specifica­tions describe paints that are unique to the military. Examples might include products such as coatings for ammunition, anti-sweat coatings for use on-board submarines, or coatings that have very low infrared signatures that will avoid detection by enemy forces. Many of these coatings are not common in the marketplace. These specifications will continue to remain in effect until commercial products become more available. Navy coatings for ships frequently have formula and specification numbers. MIL-DTL-24441 includes formulas 150 through 162. A few JAN (Joint Army-Navy) specifications, forerunners of the MIL specifications, are still used. Military specifications, standards, and qualified products lists can be obtained from the Naval Publications and Forms Center.

There are a few specifications that have been issued by other federal agencies. These agencies include the Maritime Administration, the Bureau of Reclamation, the Corps of En­gineers, and the U.S. Postal Service. These specifications are only used by the issuing agency, and many are being canceled in favor of alternate government or industry specifications. Many of these specifications have been changed to federal or military specifications. Specifications of such groups as the SSPC and the American Association of State Highway and Transportation Officials (AASHTO) are also used by federal agencies.

Items that are frequently useful in preparing contracts include paint specifications, guide specifications, type specifications, and Military and Federal Construction Guide Specifications. Purchase descriptions cover items for a single procurement. Type and guide specifi cations provide information covering a description of services required for construction or maintenance of structures such as bridges, storage tanks, and buildings.

The Department of Defense Index of Specifications and Standards (DODISS) is published annually with cumulative bi-monthly supplements for each part (Part I – Alphabetical List­ing; Part II – Numerical Listing). It is available at a subscription rate from the U.S. Government Printing Offi ce. An additional charge is required for foreign mailing. The Federal Supply Classification Listing (a cumulative listing of documents alpha­betically within their FSC classes) is also available from the U.S. Government Printing Office at a subscription rate with an additional charge for foreign mailing (available on the internet at www.dodssp.daps.mil.) Another useful internet source for government specifications is Assist Online at http://astimage. daps.dla.mil/online/.

5. Other Paint Specifications and Standards
In addition to the Federal Government, many other agen­cies, both public and private, issue paint specifications. SSPC refers to other useful public specifications whenever they are available, and has also cooperated in preparing many private specifications for special purposes. Organizations that issue standards related to painting steel are listed below. A more complete list with addresses, phone/fax numbers, and email addresses can be found in the appendix at the end of this volume.

*ASTM International has been extremely active in prepar­ing specifications for paint materials and for standard test methods for paints and materials. A complete index of all ASTM standards, listed by title, is available from ASTM at their web site (www.astm.org).

*The American National Standards Institute (ANSI) has issued a number of specifications concerning safety pre­cautions to be maintained in cleaning and painting and in the use of toxic materials. An index to their standards may be procured free or found on the internet at www. ansi.org.

*The Canadian Government Specifications Board (CGSB) has issued a number of specifications dealing with paints, cleaning, and painting materials. An index is available on the internet at www.pwgsc.gc.ca.

*The British Standards Institution (BSI) has issued a number of applicable specifications. A list of BSI standards can be found on the internet at www.bsi.org.uk.

*The American Water Works Association (AWWA) has issued specifications for the painting of water tanks and also for coating of pipelines. Their internet address is www.awwa.org.

*The American Association of State Highway and Trans­portation Officials (AASHTO) has issued specifications for paints and the painting of highway bridges and other structures. Their internet address is www.transportation. org.

*The American Welding Society (AWS) issues standards relating to safety practices, application, and materials for welding. Visit www.aws.org.

*The Master Painters Institute (MPI) has a large approved lest of architectural and industrial coatings. Its web site is www.paintinfo.com.

6. Other Generic Types of Paints and Coatings
A number of special coatings have not been fully covered in the SSPC painting systems. Because of the considerable interest in these materials, they will be discussed briefly here.

Many of these are available under Federal or Military specifi­cations. Excellent proprietary products are available for all of them. In every case, the directions of the manufacturer should be followed for application and use. Some of the principal generic types are listed below in alphabetical order.

6.1 COAL TAR COATINGS: Coal tar has been used to make hot- and cold-applied protective coatings for more than a century. The solvent-dispersed cold coatings, known as cut­backs, may be filled or unfilled. Hot-applied enamels are used over cutback coal tar primers or synthetic quick dry primers. Coal tar coatings have excellent water resistance and are, therefore, very suitable for water immersion or underground usage. They have poor resistance to ultraviolet light unless topcoated with a coal tar emulsion. Thick film mastic type coal tar coatings are covered by MIL-C-18480. The Bureau of Rec­lamation formerly used CTP 3, Coal Tar Paint; but since this specification has been canceled, they now rely on a qualified products list (QPL). The fi lled type coatings described in MIL­C-18480 are covered by SSPC-Paint 33.

AWWA Specification C 203, Coal-Tar Protective Coatings and Linings for Steel Water Pipelines – Enamel and Tape – Hot Applied, is extensively used in potable water systems, tanks, and pipelines (see SSPC-PS 10.01 and 10.02).

6.2 EPOXY MASTICS: Epoxy mastics are usually used in situations where blast cleaning is impossible or where the degree of blast cleaning is less than desirable. In other words, they serve as a surface tolerant coating going over margin­ally cleaned surfaces and most weathered coatings. In many instances, epoxy mastics have been specified in place of red lead alkyds for use over hand-cleaned steel.

Epoxy mastics are typically high solids, low VOC coatings that can be applied in thick coats by brush, roller, airless, or air spray. Typical thickness is 100 to 175 micrometers (4 to 7 mils) per coat. They can serve as a primer/topcoat or as a primer for epoxy, chlorinated rubber, vinyl, or urethane topcoats. These coatings are not recommended for immersion service.

Although SSPC does not have an epoxy mastic paint specification, per se, there is an aluminum epoxy painting system that can be used over hand cleaned or blast cleaned steel. This performance based painting system, SSPC-PS 26.00,”Aluminum Pigmented Epoxy Coating System for Steel Surfaces, Performance-Based,” can be found in Chapter 3.

6.3 GREASE PAINTS: In SSPC’s experience, grease paints have been used with only mixed results. They give temporary protection in mild areas at low initial cost. They have considerable ease of application, especially in inaccessible spots. The protection they have afforded, however, has not been equal to that of the hard-drying types of paints. Diffi culty of inspection, appearance, lack of hiding, and slipperiness are further limitations.

6.4 HIGH-TEMPERATURE SILICONE BASED COAT­INGS: The type of coating required will depend upon the desired color and pigmentation, the maximum temperature reached by the substrate, and whether operation at this temperature is intermittent or continuous. In addition to providing protection at elevated temperatures, the coatings should provide protection from the effects of weather between periods of heating.

The substrate should be cleaned of all oil, grease, and other contaminants. For best results, blast clean the surface to at least SSPC-SP 10 (near-white). The surface profi le should not be more than half of the total dry film thickness. If a primer is used to enhance adhesion between the substrate and topcoat or for increased protection under damp or chemically corrosive environments, the primer must also be heat resistant. The need for and choice of primers are based on the projected service environment.

The choice of specific paints for specific jobs will depend on operation conditions and service properties desired. The application temperature should be from 10 to 49°C (50 to 120°F). The cure required will vary from room temperature with unspecified time to specified elevated temperature and/or cure time. The paint supplier should be contacted for specific cure requirements.

TEMPERATURE (°C)

TEMPERATURE (°F)

COATING SYSTEM TYPE

120 to 200

250 to 400

Silicone-modified organic (colored)

200 to 320

320 to 430

430 to 540

540 to 760

400 to 600

600 to 800

800 to 1000

1000 to 1400

Silicone-modified organic (aluminum); Silicone-modified organic (colored); Organic-modified silicone (colored) Organic-modified silicone (black and aluminum); Silicone (colored) Silicone (black); Silicone (aluminum) Silicone ceramic; Silicone-modified organic 15-50% silicone; Organic-modifi ed silicone 50-90% silicone

1 100 hours minimum.

At operating temperatures between 120°C and 320°C (250°F and 600°F) a total dry film thickness between 100 to 150 micrometers (4 to 6 mils) is suggested. Between 320°C and 650°C (600°F and 1200°F) a total dry film thickness of 25 to 100 micrometers (1 to 4 mils) is recommended. The specific dry fi lm thickness recommendations should be obtained from the coating manufacturer’s literature. General guidelines are given in Table 3.

In the pigmentation of heat-resistant paints, it is important to use heat-resistant pigments. The majority of paints above 260°C (500°F) use inorganic or metallic pigments. The follow­ing specifications are currently available:
TT-P-28 Paint, Aluminum, Heat Resisting (1200°F, 650°C).
MIL-P-14105 Paint, Heat Resisting (For Steel Surfaces)

The aluminum paint in TT-P-28 must contain some silicone and protect the substrate to 650°C (1200°F). The silicone-ceramic paint in MIL-P-14105 must perform at temperatures up to 760°C (1400°F).

6.5 MASTICS: These heavy coatings, usually 6 mm (0.25 inch) or more in thickness, provide a thick, impervious barrier coat that excludes moisture and vapors. Common types are based upon bitumens, oils, low molecular weight vinyls, other synthetic resins, natural resins, or synthetic rubber. They are often used with a filler of a thixotropic agent to provide heavy film thickness and very high solids.

6.6 METALLIZING: Sprayed metal coatings are discussed in detail in Volume 1 of the SSPC Painting Manual and in SSPC-CS 23.00, Specification for the Application of Thermal Spray Coatings (Metallizing) of Aluminum, Zinc, and Their Alloys and Composites for the Corrosion Protection of Steel. Metallizing is that subset of thermal spraying wherein a metal feedstock material is heated, atomized, and the molten particles propelled to the substrate forming the thermal spray coating (TSC). The thermal spray gun generates the necessary heat by using combustible gases or an electric arc. As the materials are heated, they are changed to a plastic or molten state and are confined and accelerated by a compressed gas stream to the substrate. The particles strike the substrate, flatten, and form thin platelets (splats) that conform and adhere to the irregularities of the prepared substrate and to each other. As the sprayed particles impinge upon the surface, they cool and build up, splat by splat, into a laminar structure forming the thermal spray coating (TSC). The bond between the substrate and the coating is primarily mechanical. The properties of the applied coating are dependent on the feedstock material, the thermal spray process and application parameters, and post­treatment of the applied coating. The application of TSCs emits no volatile organic compounds, needs no drying time, and can be applied in low- and high-temperature environments.

6.6.1 Zinc and Aluminum TSCs: Zinc, aluminum, and zinc-aluminum alloy coatings are used for a wide variety of corrosion-control applications in industrial and marine environ­ments. They provide significant corrosion protection, up to and greater than 20 years to first maintenance. They are anodic to steel and provide sacrificial protection. When they are applied thickly enough so that porosity does not extend from the surface to the base metal, They also provide barrier protection. In this respect zinc is a much more active metal than aluminum. On the other hand, aluminum has a lower chemical activity, an adherent oxide film, and a higher electrical resistance than zinc. Aluminum also provides longer term protection along with better high-temperature and abrasion/wear resistance. Alloys of the two metals have properties somewhere in between, depending on the ratio of zinc to aluminum. An 85/15 (percent by weight) alloy of zinc and aluminum is a widely used TSC material because it combines attributes from both metals.

6.6.2Arc and Flame Spraying: Arc- and flame-wire spray­ing are the primary methods for metallizing steel components and structures. In arc spraying, two insulated consumable electrodes, at 18 to 40 volts potential difference, advance to meet in an atomizing gas stream. The high-temperature-arc heat source melts the wires and a compressed air stream atom­izes and propels the molten particles to the substrate forming the TSC. In flame spraying, the wire advances through an oxygen fuel-gas heat source melting the wire. A compressed air stream atomizes and propels the molten particles to the substrate forming the TSC. Arc spraying is generally more cost-effective than flame spraying providing higher spray rates and lower energy costs.

6.6.3 Sealing and Painting: Aluminum and zinc TSCs have porosity ranging up to 15 percent. Interconnected po­rosity may extend from the surface to the substrate. Sealing extends the service life. Sealing is accomplished two ways:

(1) naturally, by the oxidation of the sprayed aluminum or zinc filling the pores with a tightly adherent oxide layer; or (2) by applying a thin low-viscosity sealer that penetrates and is absorbed into the pores of the TSC. Sealers should be applied before significant natural oxidation occurs. Liquid seal coats must be suitably thinned and have a fine-pigment grind to ef­fectively flow into the TSC. Sealers improve the appearance and reduce the retention of dirt and other contamination, but they do not degrade the cathodic protection of the TSC. Sealed TSCs should be painted only when:

  1. The environment is very acidic or very alkaline, i.e., when the pH is outside the range of 5 to 12 for zinc and zinc alloy TSCs or 4 to 9 for aluminum TSCs.
  2. The metal is subject to direct attack by specific chemicals.
  3. The required decorative finish can be obtained only with paint.

*Additional abrasion resistance is required. Common sealers include many of the synthetic resin coat­ing systems, especially vinyls, epoxies, polyurethanes, and phenolics. High-viscosity, thick film coatings should never be applied directly to an unsealed thermal spray coating.

When TSCs are applied as a sacrificial anode, a liquid seal coat is usually not used. However, a very thin liquid seal coat may be used if it is less than 25 micrometers (1 mil) thick. This will maintain the electrical path between the TSC and the substrate steel. When TSCs are applied as a distributed anode for an impressed current cathodic protection system, a liquid sealer or topcoat should not be applied.

6.7 NON-SKID COATINGS: Any type of paint that is suitable for application on floors can be converted to a skid resistant paint by incorporation of a finely divided material such as silica, aluminum oxide, or ground shells.A-A59166, Coating Compound, Nonslip (for Walkways) is a Federal performance specification that must have weather and impact resistance, in addition to providing a high friction surface.

6.8 NEOPRENE: Neoprene is a synthetic elastomer which is soluble in aromatic hydrocarbons and is used as a vehicle for protective coatings. It has high elasticity, good aging, and chemical and solvent resistance. The proprietary neoprene coatings may be divided into two general types: (a) two-part high solids heavy duty coatings and (b) one-part self-priming coatings.

The two-part high solids coatings, which are usually based on “Neoprene KNR,” have comparatively poor adhesion even to blast cleaned steel and are generally used over chlorinated rubber primers. They require addition of vulcanizing and ac­celerating agents prior to application. Typical specifications for such a coating have been proposed: solids content 54 to 58% (of which at least 50% would be neoprene), specific gravity 1.1 to 1.2, viscosity at 25°C (77°F) is 1750 to 2500 centipoise, and a dry film thickness of at least 125 micrometers (5 mils).

Lower solids, self-priming maintenance coatings, usually based on “neoprene AC,” have about as much solids as the heavily liquid neoprene coatings. These coatings contain all curing agents and nothing need be added on the job. They have fair storage stability. The coatings are of the order of 2 mils (50 micrometers) dry film thickness. The neoprene “AC” coatings have less chemical and abrasion resistance than the vulcanized “KNR” coatings.

6.9 POLYESTER COATINGS: Polyester vehicles are based upon a condensation reaction between an acid and an alcohol, one or both being unsaturated. The resulting pre-poly­mer is dissolved in styrene and uses a peroxide catalyst and an accelerator to bring about poly-addition and cross-linking reactions. The styrene solvent reacts with the polyester during curing so that no solvent evaporation is necessary. Depending upon the choice of the catalyst, these products may be cured at room temperature or by baking. A wide range of properties can be obtained by using rigid, semi-rigid, flexible, corrosion-resistant, or fire-retardant resins.

In addition to these conventional polyesters, a fully satu­rated linear polymer may be obtained, such as that formed from terephthalic acid, suitable for tapes and foils. This type will not be discussed here. Discussed separately under urethanes is the type of polyester that reacts with diisocyanates to form polyurethane.

The common polyesters are almost always reinforced with glass fiber, cloth, asbestos, micaceous pigments, etc., to absorb shrinkage strains and to compensate for the brittle character of the resins. Small amounts of wax may also be added to the polyester at the time of manufacture to overcome its tendency toward air inhibition of the normal curing of the polyester mass.

The polyester may be made up as a two-package system. Mixed shortly before use, one package contains the promoter, such as cobalt naphthenate, and the other the peroxide catalyst or initiator. A three-package system is also available consist­ing of polyester, catalyst, and promoter. These resins may be applied with a two-nozzle spray gun that mixes the reactive ingredients in the spray pattern. A third nozzle may be used to incorporate short glass fiber into the wet film.

6.10 POLYETHYLENE COATINGS: Solid polyethylene has excellent resistance to all chemicals except for strong oxidizing agents, oils, and chlorinated and aromatic solvents. Since this resin is available in powdered form, heavy thick­nesses can be applied. It should not be assumed, however, that the coatings have the impermeability of a calendared film of equal thickness. Nevertheless, proper application by fluidized bed or by flame spray can result in a durable, economical, and attractive coating.

The surface is preferably prepared by blast cleaning, and the metal is ordinarily pre-heated to approximately 220°C (425°F) before application of the resin. For corrosive applica­tions, the coating should be tested for pinholes by a static spark tester. Flame spraying tends to oxidize the resin nearest the hot surface, improving adhesion but tending to decrease impermeability and chemical resistance at that point. The coating has excellent anti-stick properties and resistance to a wide range of chemicals.

Although atmospheric weathering of these films is usu­ally good, it will vary considerably with small variations in formulation. Weather durability is similar to that of chemically related alkyds. Water and moisture resistance are excellent and these coatings are widely used in salt and fresh water exposure. Polyethylene coatings adhere well to steel that has been deeply etched or blast cleaned to provide the necessary mechanical roughness.

6.11 SILICONE ORGANIC COPOLYMERS: Silicone coat­ings have been well known for some time for their good color and gloss retention when exposed to exterior weathering.They are discussed under high temperature silicone-based coating. Unmodified silicones, however, are expensive and must be cured at 200-260°C (400-500°F). Air drying properties, lower cost, hardness, and adhesion are obtained by copolymerizing silicones with organic polymers. The copolymers show practi­cally no film erosion, and therefore, are very slow to chalk.

6.12 TAPES: Many kinds of tapes are widely used in the protection of underground piping. Some of these, including vinyl and polyethylene tapes, have also been used in the protection of other kinds of structural steel. Widths range up to several feet; tape may either have pressure sensitive backing or require separate adhesive for application. Some of these tapes have good resistance to weather and brine, if carefully lapped, but have poor resistance to abrasion or cutting. Common types are discussed in the chapter on underground coatings in Volume 1 of the SSPC Painting Manual.

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