Painting System Overview
Guide To Using SSPC Painting System
SSPC has three types of painting system documents: complete painting systems, painting system guides, and performance-based painting system material specifications. The SSPC documents of this type were developed only for steel, not for wood or concrete.
Painting System: Each of these painting systems combines in a single specification all of the requirements necessary for a complete paint job. It therefore includes by reference all of the specifications for surface preparation, paint application, paint thickness measurement, primer, mid-coat, topcoat, safety, and inspection. In most cases it is recommended that the particular painting system is specified by number.
Painting System Guides: The painting system guides are to be used to prepare modified systems for special cases. Unlike the other guides in this section, SSPC-Guide 8.00 does not address the surface preparation of a steel substrate, but rather provides guidance in selecting the proper topcoat for use over a zinc-rich primer.
Painting System Material Specifications – Performance-based: These documents specify the performance requirements for a multi-coat system based on a particular generic class of coatings, e.g., aluminum epoxy. These documents serve only to qualify a coating material and do not address other items such as surface preparation and thickness measurement. Hence, these painting system material specifications serve only to specify the coating material to be used in a complete painting system specification.
By disregarding the more unusual combinations and circumstances, the SSPC Painting Systems are able to offer in complete but compact form the minimum number of combinations necessary to paint the great preponderance of steel structures. For unusual circumstances, users of the specifications may devise their own painting systems by choosing from among the alternative specifications listed in the Painting System Guides. These models offer a large number of compatible combinations of surface preparations, primers, intermediates, and finish paints.
SSPC Painting Systems and Guides were originally published in 1955. They were revised and expanded to incorporate improvements in concept and in technology. The Painting System Material Specifications – Performance-Based were first introduced in 2000. The descriptions of painting systems are listed in Table 1. Within each generic type, there may be several systems, each a complete paint scheme in itself. Each scheme is designed for a specific application where a particular combination of durability, drying time, tolerance for surface preparation, cost, color, etc., is desired.
2. Using SSPC Painting Systems by Number
The preferred method of using the SSPC Painting Systems is simply to specify, for example, that the steel or the structure shall be painted in accordance with the SSPC-PS 1.09 “Three Coat Oil Base Zinc Oxide Painting System.” This is similar to the procedure that would be used in specifying the steel.
By using this method, the specifier can procure a standard painting system consisting of a surface preparation suitable for the priming paint; the specification for an intermediate coat (sometimes a primer or top-coat tinted to contrasting shade); usually one standard finish coat, often offering an option of colors and a specified thickness for each coat. Use of the standard painting system will generally result in satisfactory performance if the recommendations are followed.
Within each general type of painting system an exceedingly large number of combinations would be possible. As an aid in selecting a specific system for a specific need, some general types are divided into a limited number of proven SSPC Painting Systems.
3. Using SSPC Painting System Guides
Rather than using the SSPC Painting System Specifications, the specifier may wish to employ the SSPC Painting System Guides. These worksheets (or models) are useful for special painting problems not covered by the standard painting systems. To use them, one first decides what generic type of coating is to be used – oil base, alkyd, zinc-rich, coal tar, etc. For each of these types there is usually a corresponding painting system guide. For example, the oil base painting system guide is numbered SSPC-PS Guide 1.00, the alkyd guide is numbered PS Guide 2.00, and so on. In these guides are descriptions of each specification, including the principal public specifications of SSPC, the government, the American Association of State Highway and Transportation Officials (AASHTO), and others. A complete painting system can therefore be made up by choosing, from one of these worksheets, the desired stipulations on surface preparation, application, primer, topcoat, etc.
TABLE 1 OUTLINE OF SSPC PAINTING SYSTEMS AND GUIDES
System Number Code Description
1 SSPC-PS 1.00-1.13 Oil Base Painting Systems 2 SSPC-PS 2.00-2.05 Alkyd Painting Systems 4 SSPC-PS 4.00-4.04 Vinyl Painting Systems 7 SSPC-PS Guide 7.00 Guide for Selecting One-Coat Shop Painting Systems 8 SSPC-PS Guide 8.00 Guide to Topcoating Zinc-Rich Primers 10 SSPC-PS 10.01-10.02 Hot- and Cold-Applied Coal Tar Painting Systems 11 SSPC-PS 11.01 Black (or Dark Red) Coal Tar Epoxy Polyamide Painting System 12 SSPC-PS 12.00-12.01 Zinc-Rich Painting Systems 13 SSPC-PS 13.01 Epoxy Polyamide Painting System 14 SSPC-PS 14.01 Steel Joist Shop Painting System 15 SSPC-PS 15.00-15.04 Chlorinated Rubber Painting System 16 SSPC-PS 16.01 Silicone Alkyd Painting System for New Steel 17 SSPC-PS Guide 17.00 Guide for Selecting Urethane Painting Systems 18 SSPC-PS 18.01 Three-Coat Latex Painting System 19 SSPC-PS Guide 19.00 Guide for Selecting Painting Systems for Ship Bottoms 20 SSPC-PS Guide 20.00 Guide for Selecting Painting Systems for Boottoppings 21 SSPC-PS Guide 21.00 Guide for Selecting Painting Systems for Topsides Guide for Selecting One-Coat, Pre-Construction or Pre-Fabrication Painting Systems for Ships Specification for the Application of Thermal Spray Coatings (Metallizing) of Aluminum, Zinc, and Their Alloys and Composites for the Corrosion Protection of Steel Latex Painting System for Industrial and Marine Atmospheres, Performance Based Aluminum Pigmented Epoxy Coating System for Steel Surfaces, PerformanceBased 27 SSPC-PS 27.00 Alkyd Coating System, Performance-Based.
By using this alternative, painting systems may be prepared to cover special requirements. It should be emphasized, however, that judgment must be used in selecting the proper painting systems, the surface preparations, and priming and finish paints. The recommended systems are completely compatible and should result in satisfactory paint life from both the protective and decorative viewpoint. Volume 1, SSPC Good Painting Practice should also be consulted for further detailed information.
The painting systems are occasionally used in a third way. This method is similar to the preceding one, but the users may vary any of the surface preparations, primer, etc., that are listed by substituting proprietary products or other specifications as desired. A painting system is then a model for the preparation of the user’s own painting system, which may be more suitable for particular requirements. Here, the user must be extremely careful that compatible surface preparations, paints, and methods are specified. The use of proprietary priming and finish paints is highly recommended provided the user has sufficient experience to know that they will perform satisfactorily.
4. Using SSPC Painting System Material Specifications – Performance-Based
These specifications are used to specify only the coating material, i.e., the paints, in a complete painting system specification. One of the SSPC Painting Systems or Painting System Guides can be used as a template in preparing the job specification incorporating the performance-based coating material specification. This approach allows the coating manufacturer to custom match each coat of a multi-coat system with the adjacent coating layer.
The use of specifications alone cannot guarantee performance; neither can strict compliance with the recommendations of the specifications prevent all future paint failures. For example, when hand cleaning is used as a method of surface preparation, it is impossible to guarantee that there will be no lifting of mill scale. Even when blast cleaning is used as a method of surface preparation, and the proper paints are used, paints may fail due to the great number of factors that cannot be controlled in every case. One can be safely assured, however, that if this good practice has been followed, the possibility of failure is reduced to the minimum consistent with the present state of the art.
Regulations governing the content of volatile organic compounds (VOC) of coatings vary from state to state and among districts within a state. Before choosing a painting system it is therefore imperative that all applicable federal, state, and local regulations and restrictions are known so that the appropriate surface preparation and coatings can be specified.
6. Summary of SSPC Painting Systems
6.1 OIL BASE PAINTING SYSTEMS (NO. 1): Oil base painting systems are summarized, which shows three basic oil base paint systems. These are numbered SSPC-PS 1.09, 1.10, and 1.13. For special paint problems not covered by the standard paint systems, an oil base painting system guide SSPC-PS Guide 1.00 is also presented.
6.1.1 Use: The oil base painting systems do not necessarily require complete removal of intact mill scale by blast cleaning or pickling. However, thorough surface preparation by hand tool or power tool cleaning is mandatory. The primers in these systems are based chiefiy upon linseed oil vehicles with good surface wetting properties and upon rust-inhibitive pigmentation.
These painting systems are intended primarily for structural steel exposed to atmospheric conditions. They are particularly suitable for outdoor weather exposure, but may also be used for the interior of buildings subjected to moderately corrosive conditions. They have only limited resistance to chemical exposure, immersion, brine, condensation, high humidity, burial, very corrosive environments, high temperatures, or abrasion. Blast cleaning or pickling may be used to prolong expected paint life, to counteract severe exposures, or to assure adequate cleaning of badly rusted steel surfaces.
These painting systems have been used successfully on a wide variety of weather-exposed structural steel constituting the major surface areas of many structures. They are satisfactory for structural steel in industrial, rural, or mild marine atmospheres. Typical structures are highway, railroad, and ore bridges; tank exteriors; building exteriors; interiors exposed to occasional condensation and fumes; bandstands, grandstand frames, and platforms; bin exteriors; belt conveyors; unheated parts of blast furnaces; catenary poles and towers; industrial plant yard areas; cranes, derricks, runways, and heavy equipment; dock and dam superstructures; fences, posts, guard rails, iron railings; fire escapes, door frames, window sills and coatings.
6.1.2 Description: Primer vehicles made up of raw linseed oil only are very slow drying (at least 48 hours to handle). Additions of boiled oil reduce the drying time but also reduce the wetting efficiency. Additions of alkyd resins further reduce the drying time but also reduce the wetting efficiency. Inhibitive pigments help retard corrosion. Other pigments enhance the functionality (hardness, UV stability, etc.) of the coating.
Each of these oil base painting systems represents a proven combination selected for specific properties and uses. System PS 2.05 provides some alkyd in the primer and is especially good for steel that is thoroughly wire brushed. Systems PS 1.09 and 1.10, three and four coat systems, respectively, use zinc oxide primers that are free of lead and chromate pigments. System PS 1.13 consists of a single coat of a slow drying maintenance primer.
If this alternate finish coat is used, then the intermediate coat shall consist of one coat of SSPC-Paint 101, Alkyd Aluminum Paint, Type II, Non-Leafing.
6.2 ALKYD PAINTING SYSTEMS (NO. 2)
6.2.1 Use: Alkyd painting systems are satisfactory for structural steel in industrial, rural, or marine atmospheres, particularly those that are too severe for oil base paints, such as high humidity, industrial fumes, etc. Typical structures are plants and refineries; moderately heated parts of blast furnaces; industrial buildings; chemical plants, yard areas or mild interiors; interiors of buildings of high humidity but not continuous condensation; bins, belt conveyors, platforms; grandstands; highway, railroad, and ore bridges; dam and dock superstructures; topsides and superstructures of vessels; cranes and derricks; guard posts and rails; and railings.
An alkyd painting system may be used for production items such as siding, door and window frames and sash, or for equipment used in highway construction, mining, and excavating. For such items, hot phosphate pretreatment or wash primer is recommended. Colored high gloss enamel finishes may be selected from proprietary sources. Where conditions are more severe than normally encountered, or faster drying topcoats are desired, alkyd finish paints should be selected rather than oil paints.
Generally, linseed oil paints or alkyds are not considered satisfactory for continuous water immersion.
When very short oil alkyds are specified for use over softer paints, it is important that at least one week of drying be allowed before application of the alkyd paint. A performance-based alkyd system is described in PS
6.2.2 Description: Alkyd painting systems are intended primarily for structural steel exposed to atmospheric conditions, but they may be used for infrequent immersion in fresh or salt water, or infrequent exposure to condensation. They are particularly suited for severe weather exposure, but they may also be used for the interiors of buildings subjected to corrosive conditions such as mild chemical exposure, high humidity, or infrequent condensation. They have only limited resistance to strongly chemical environments, complete immersion, burial, or severe abrasion. Because of the reduced performance of the primers on dirty, oily, or rusting steel, it is recommended that blast cleaning or pickling of steel be used as the surface preparation for new work.
TABLE 2 OIL BASE PAINTING SYSTEMS (FOR WEATHER-EXPOSED, WIRE-BRUSHED STEEL)
SSPC 1.09 SSPC-PS 1.10 SSPC-PS 1.13 Zinc Oxide Primer Zinc Oxide Primer Slow Drying Maintenance
6.3 VINYL PAINTING SYSTEMS (NO. 4)
6.3.1 Use: SSPC vinyl painting systems are intended for very severe exposures. They are satisfactory for most of the severe chemical atmospheres; they may be used with discretion for immersion in corrosive chemicals such as inorganic acids, alkalis, and salts; or liquids such as aliphatics, alcohols, oils, grease; but they are dissolved by some organic solvents such as aromatics, ketones, ethers, and esters, and attacked by some chemicals such as fuming nitric acid, 98 percent sulfuric acid, and acetic acid. Solution vinyls are seldom used today because of their high VOC contents.
These painting systems are recommended highly for complete or alternate immersion in fresh (including potable) or salt water, high humidity and condensation, and exposure to the weather. They are also particularly suitable for the interiors of buildings where flame resistant, mildew-free, easy to clean corrosion resistant paints are desired.
Because of the great increase in paint life, blast cleaning or pickling of the steel is the minimum recommended surface preparation for new work. In maintenance painting when only small areas need to be cleaned, hand or power tool cleaning may suffice.
Vinyl painting systems are recommended for floor systems of bridges exposed to brine drippings or deicing salts, for potable water tanks, and for most chemical exposures including dry ladings of chemicals. They are not generally recommended for constant immersion at temperatures in excess of 49°C (120°F); they may be used at temperatures up to 85°C (185°F) for atmospheric exposure, spillage, or short or infrequent immersion.
NACE International makes general observations on the chemical resistance of vinyl chloride-acetate copolymers in their report T-6B-10, “Vinyl Coatings for Prevention of Atmospheric Corrosion,” Materials Protection, Vol. 2, No. 6, pages 96-100, June 1963.
6.3.2 Description: The vinyl painting system guide, SSPC-PS Guide 4.00, may be used to draw up vinyl painting systems when special properties other than those in the standard system SSPC-PS 4.04 are required.
Care and skill must be exercised in the application of vinyls, especially when open to the wind. In general, however, SSPC has found them excellent in water immersion and in other recommended applications.
A wash primer improves adhesion to less than adequately prepared surfaces, and it tends to prevent corrosion creepage in salt water. The wash primer itself, however, is not as resistant to acids and alkalis as the copolymer vinyl. Reportedly, it is prone to osmotic blisters in warm, fresh water, a tendency that can be largely nullified with an aluminum topcoat. Although many users still recommend a wash primer in fresh water exposure, this practice is no longer thought to be necessary or desirable.
The profile depth of the blast cleaned surface is important to vinyl paint systems. Here the recommendations in the SSPC Surface Preparation Commentary should be followed carefully because vinyl paint life can be extended by careful surface preparation. White metal blast cleaning is often recommended for vinyl systems. Because of excessive cost and difficulties reported in obtaining white metal cleaning, however, these paint systems often permit the use of near-white or commercial blast cleaning.
All welds and all areas adjacent to welds must be thoroughly blast cleaned. Consult the SSPC Surface Preparation Commentary for additional details.
The proper techniques for applying vinyl paints are given in SSPC-PA 1, “Shop, Field, and Maintenance Painting of Steel,” and in the literature of the suppliers. Airless spray and hot spray with multiple passes are helpful in obtaining proper thickness without sagging or pinholing. However, when the thickness per coat exceeds the recommended thickness by too great a margin, entrapment of solvent with subsequent pinholing may be encountered. The painter must operate close enough to the work to lay down a wet film.
Using high solids vinyl paints results in a greater film thickness per coat than is obtainable with these SSPC systems. Such paints may also have the advantage of lower cost due to less expensive resins, higher amounts of extender, and lower amounts of solvent. Nevertheless, the higher solids (and consequently greater film thickness) are obtained by using lower molecular weight resins that sacrifice some resistance and durability.
The vinyl aluminum topcoat is preferred for water immersion. It is not, however, recommended as an intermediate coat or primer in vinyl systems for application in thick films, due to the possibility of solvent entrapment. As indicated, it should not be used in caustic or strongly acid exposures.
6.4 ONE-COAT SHOP PAINTING SYSTEMS FOR STRUCTURAL STEEL (SSPC-PS GUIDE NO. 7.00)
6.4.1 Use: One-coat shop painting systems are intended for use in dry, non-corrosive environments, such as structural steel enclosed in masonry, interiors of buildings where temperature rarely falls below the dew point, or where relative humidity does not exceed 70 percent, outdoor exposure in arid climates, or temporary weather protection (less than six months) in rural or light industrial areas.
These one-coat painting systems are not expected to protect steel exposed to the weather for periods longer than six months in normal rural and mild industrial areas, and even shorter exposure periods for heavy industrial or marine exposures. These one-coat systems are intended for building frames to be enclosed in masonry or non-corrosive fireproofing, but paint should not be used if bonding of steel to concrete is required. These systems can also be used for open frames or structural steel in buildings not subjected to high humidity, condensation, or corrosive fumes; walls and partitions; floor joists and roof trusses; window and door frames; bins, ducts, chutes, conveyors, railings, platforms, runways for interiors of buildings, or exteriors where either short term protection is desired or additional painting will be undertaken.
6.4.2 Enclosed Steelwork: In building construction, steelwork enclosed in masonry in non-corrosive areas is sometimes left unpainted. The surface condition of such steel framing in many long-standing buildings has been excellent except in isolated spots where leakage may have occurred. Where such leakage is not eliminated, the presence or absence of a shop coat is considered of minor infiuence.
6.4.3 Description: The surface preparation for one-coat shop primers consists of hand cleaning of the steel to remove very detrimental foreign matter, loose mill scale, loose rust, accessible weld slag, and heavy deposits of oil and grease. Proprietary primers may be specified by the purchaser or used by the fabricator if agreed upon by the purchaser.
6.5 TOPCOATING ZINC-RICH PRIMERS (SSPC-PS GUIDE 8.00)
6.5.1 Use: This guide covers the selection and application (including surface preparation) of topcoats to surfaces coated with a zinc-rich primer. Both organic and inorganic primers are included. The guide does not cover the selection and application of the zinc-rich primer.
6.5.2 Description: Zinc-rich primers are topcoated to provide extended exterior durability in severe exposures; to improve color, gloss, and other appearance properties; and to provide resistance to specific conditions such as highly acidic or highly basic environments.The guide contains a chart showing the degree of compatibility or non-compatibility between generic types of topcoats and zinc-rich primers.
6.6 COAL TAR PAINTING SYSTEMS (NO. 10): Painting system SSPC-PS 10.01 covers one type of hot-applied coal tar enamel, and SSPC-PS 10.02 covers one type of cold-applied coal tar mastic. The properties and uses of these two systems are somewhat different.
6.6.1 Use: The hot-applied coal tar system PS 10.01 consists of commercial blast cleaning (or pickling), one prime coat and two finish coats of hot-applied coal tar enamel. This painting system is intended primarily for underwater or underground use. For exposure to sunlight, it requires a topcoat of coal tar emulsion to reduce checking and alligatoring. The painting system has good abrasion resistance and is suitable for pipelines, hydraulic structures, piling, underground tanks, water tank interiors, sheet piling, corrosive interiors, underground or submerged portions of barges and dry docks, aeration and humidifying equipment, ballast tanks and bilges, classifiers, coal washers and culverts. It is, however, dissolved by some organic solvents and attacked by some oxidizing solutions.
The cold-applied coal tar system PS 10.02 is typically applied to barges, dry docks, aeration and dehumidifying equipment, ballast tanks and bilges, piling, classifiers, coal washers, floatation equipment, culverts, dams and flood gates, floats and pontoons.
6.6.2 Description: Painting System 10.01 requires a hot-applied primer as specified in AWWA C 203 (synthetic type). It is followed by a coat of coal tar enamel applied, usually in two coats, to a total thickness of 2.4 ± 0.8 mm (3/32 ± 1/32 inch). Where potable water is being used, AWWA C 203 is applicable. Experienced and skilled workers are required to apply this system properly.
Painting System No. 10.02, Cold-Applied Coal Tar Mastic, is used for steel structures in corrosive environments. It requires commercial blast cleaning (or pickling) followed by two coats of MIL-C-18480, “Coating Compound, Bituminous, Solvent Coal Tar Base.” All areas exposed to sunlight must then be top coated with a suitable topcoat, such as SSPC-Paint 32.
6.6.3 Other Specifications and Properties: The types of coal tar coatings are parallel to those of asphalt coatings, including cutbacks of coal tar pitch in solution, filled or unfilled, and hot-applied enamels (no filler) used over a cutback coal tar primer.
Coal tar coatings have better water resistance than asphalt and are superior to asphalt for a given thickness in underground burial. Coal tars are poorer than asphalt, however, in weather resistance (unless emulsion topcoated) and in acid resistance.
American Water Works Association Specifications C 203 for coal tar primer and coal tar enamels are extensively used. Coal tar pitch may be applied as a hot melt over coal tar primer.
Coal tar paints and field coatings, primer and hot enamel are procurable under MIL-C-18480, “Coating Compound, Bituminous, Solvent, Coal Tar Base.”
The most recent SSPC coal tar specifiare SSPC-Paint 32, “Coal-Tar Emulsion Coating,” and SSPC-Paint 33, “Coal Tar Mastic, Cold-Applied.” Paint 33 is for use underground or underwater and must be topcoated with Paint 32 if it exposed to the atmosphere. Paint 32 is a weather coat and may be applied hot or cold.
6.7 COAL TAR EPOXY PAINTING SYSTEM (SSPC-PS 11.01)
6.7.1 Use: This SSPC painting system consists of two coats of the specified polyamide coal tar epoxy paint applied to a near-white blast cleaned structural steel surface. It is used on structural steel in marine or chemical environments, buried tanks and pipes, immersion in fresh or salt water, tidal zone, splash zone, weather zone, and for the interiors of tanks containing crude oil, salt brine, or unrefined petroleum products.
6.7.2 Description: Coal tar epoxy paint as made by its numerous manufacturers is a material of rather widely varying characteristics with respect to curing, pot life, odor, viscosity, ease of application, and performance.
Coal tar epoxy coatings are heavy bodied, thixotropic materials with a high non-volatile content on the order of 85 percent or more by weight. These characteristics permit heavy applications ranging up to 250 micrometers (10 mils) or more dry film thickness per coat, provided field thinning is held to a minimum. These materials may be brush or spray applied. Spray equipment may be of the conventional air-atomizing type if modified to include a large diameter material hose, a large orifice nozzle, and material pump or bottom withdrawal pot. High pressure airless spray equipment is also being used with good results on flat surfaces. The coal tar epoxy coatings are usually applied without a special primer in two coats to a minimum dry film thickness at any point of 400 micrometers (16 mils) over commercial or near-white blast cleaned surfaces. They should not be applied unless the metal and ambient temperatures at the time of application are above 10°C (50°F) and unless it can be anticipated that an average temperature of 10°C (50°F) or higher will prevail for several days after application. The curing time between coal tar epoxy coats should not exceed a day or two, particularly in hot weather, if the possibility of poor intercoat adhesion is to be avoided. In maintenance repainting or in repairing damaged areas, the attainment of good adhesion between old and new paint may be troublesome unless the undercoat is thoroughly cleaned and roughened by brush-off blast cleaning.
Coal tar epoxy coatings tend to become increasingly hard during the early years of exposure, but there is no indication when applied to steel of moderate and heavy cross-section that they will eventually become critically infiexible. Coal tar epoxy coatings on steel surfaces are capable of providing long term protection in situations involving fresh water immersion, condensation, sea water immersion, tidal and splash zone exposure, burial in the soil, and exposure to brine, salt, crude oil, sewage, and some chemicals. They are considered to be reasonably durable in ordinary weather exposure and may become more so if the final coat of coal tar epoxy is formulated to contain some aluminum pigment or if topcoated with a compatible aluminum paint. Coal tar epoxy coatings, if given plenty of curing time before exposure, are resistant to the erosive action of high velocity water but are not as resistant to gouging by waterborne ice and massive debris as the best of other coatings are. Gouge resistance may be improved by filling or reinforcing with garnet or other sandlike particles in the 30-70 sieve size range.
Coal tar urethane coatings having properties somewhat similar to coal tar epoxy paints are available.
6.8 ZINC-RICH PAINTING SYSTEMS (NO. 12)
6.8.1 Use: Zinc-rich coatings may be used in a variety of environments, but are mainly intended for use in conditions of high humidity or marine atmosphere exposures, both exterior and interior, and for fresh water immersion. With appropriate top coating, they may be used for brackish and sea water immersion and for exposure to chemical fumes. Some untopcoated inorganic zinc-rich coatings have been used successfully in ballast tanks where they are subjected to salt water immersion.
6.8.2 Description: The Guide to Zinc-Rich Coating Systems, SSPC-PS 12.00, is based primarily upon performance. The One-Coat Zinc-Rich Painting System, SSPC-PS 12.01, specifies SSPC-Paint 20, “Zinc-Rich Primers, (Type 1, “Inorganic” and Type II, “Organic”) or SSPC-Paint 29, “Zinc Dust Sacrificial Primer, Performanced-Based.” Zinc-rich coatings are heavily pigmented with metallic zinc to form an electrically conductive coating. Long-term protection is by a barrier mechanism. This is supplemented by galvanic protection from the zinc at scratches or breaks in the paint film. Zinc corrosion products formed in providing this protection tend to block small breaks in the coating to sustain barrier protection. To obtain such galvanic action from coatings, it is necessary to have a high percentage of zinc in the dry film. SSPC-Paint 20, Paint 29, and Paint 30 all require a minimum of 65 percent zinc by weight in the dry film.
The vehicle composition of zinc-rich paints described in SSPC-Paints 20 and 29 may be either organic or inorganic. Depending upon the skill of formulation, good results have been obtained with a wide variety of vehicles including inorganics such as zinc silicates and phosphates, and organics such as epoxies, chlorinated rubber, and polyesters.
Some properties depend on the type of vehicle. However, zinc-filled coatings are unsuitable for acid service without suitable topcoats and their alkali resistance is also very limited. The inorganic coatings have outstanding ability to withstand exposure to solvent, oils, and petroleum products. They are also unaffected by aliphatics, aromatics, ketones, or alcohols. They resist dry chlorinated hydrocarbons, but are attacked by wet chlorinated solvents that release hydrochloric acid. They are very resistant to high humidity, splash, and spray, but most types should be sealed or topcoated for continuous salt water exposure. For high temperature service, the recommended maximum is 60°C (140°F) wet, or 370°C (700°F) dry. Abrasion and impact resistance, as well as oil resistance, have proved excellent in SSPC tests. Weathering of the inorganic zinc-rich coatings is considered excellent, as the coatings continue to cure during prolonged exposure.
Inorganic zinc-rich coatings are available in one-, two-, and three-package forms. The two-package materials are called self-curing and consist of zinc dust mixed with the inorganic vehicle just before application. With some coatings commercial blast cleaning (SSPC-SP 6) is considered satisfactory, while others require near-white blast cleaning (SSPC-SP 10).
The three-package, or post-cured, material consists of zinc dust stirred into the inorganic vehicle shortly before application. This coating is then very vulnerable to rain or other water until the curing solution (usually acid-based) is applied. Near-white blast cleaning is considered the minimum surface preparation. The resulting surface of both self-curing and post-curing types has no gloss and is similar in appearance to weathered galvanized steel.
Organic zinc-rich coatings are also available in one-, two, and three-package forms. The three-package material consists of zinc dust, resin component, and curing agent, which are mixed and applied to a thickness of 50 to 100 micrometers (2 to 4 mils). This coating is then somewhat vulnerable to rain until the solvents have essentially evaporated. The resulting surface has no gloss and resembles weathered galvanized steel. Two-package is the same as three-package except that the zinc is incorporated into one of the two parts of the vehicle and the remaining part is added before application. One-package is completely mixed in one container and ready to use. Many of the organic zinc-rich formulations have rapid air-drying rates. Others are cured by baking. Near-white blast cleaning (SSPC-SP 10) is considered advantageous, although commercial blast cleaning (SSPC-SP 6) is sometimes specified.
6.9 EPOXY PAINTING SYSTEM (SSPC-PS 13.01)
6.9.1 Use: Epoxy-Polyamide Painting System, SSPC-PS 13.01, consists of application of a polyamide epoxy primer, intermediate and finish coat (SSPC-Paint 22) to commercially blast cleaned steel (SSPC-SP 6). The required SSPC paint specifications are based upon performance tests of primer and topcoats formulated within specified composition limits. The system is designed for industrial exposure, marine environment, areas subject to chemical exposures, and areas frequently wet by fresh and salt water.
SSPC-PS 13.01 is based upon three coats of polyamide catalyzed epoxy paint (SSPC-Paint 22) which has specifications based on a combination of performance and composition requirements. The stipulations for interval between coats are believed to be important in order to achieve good intercoat adhesion. For this reason, it is not recommended that the primer be applied in the shop and the remainder applied during construction.
6.9.2 Description: The epoxies are a versatile family of resins having good flexibility, hardness, toughness, adhesion, and high solids. There are two basic types of air-drying epoxies: amine-cured and polyamide-cured. Epoxy esters are not considered to be epoxies but are drying oil coatings. Amine adducts merely have the amine curing agent partially reacted with the epoxy resin.
The epoxy ester is obtained by modifying the resin with a vegetable oil fatty acid. These paints require no curing agent, and they are considered competitive for general plant maintenance with the other oil-modified paint systems such as alkyds, with good color retention, ease of application, some chemical resistance, but poor gloss retention. With properly formulated epoxy esters, thorough hand tool cleaning (SSPC-SP 2) may be used as a surface preparation in shop or maintenance painting of steel that is not heavily rusted. Commercial (SSPC-SP 6) or near-white (SSPC-SP 10) blast cleaning is recommended for the amine or polyamide catalyzed epoxy.
With epoxy amines, the curing agent is added just prior to use, thereby permitting the application of a fairly thick, very adherent film that dries through fairly rapidly at 15°C (60°F) or above. Amine cured epoxies have excellent resistance to chemicals, non-oxidizing acids, brine solutions, certain organic products, and heat.
Epoxy formulations using the polyamide type of curing agent exhibit less overall chemical resistance but better water resistance, color retention, and flexibility when compared with either the amine or amine adduct curing agent. They also have a less critical ratio of components (usually 1:1), are considered non-toxic, and are less affected by poor surface preparation, handling, and application. Amine cured epoxies can be applied in single coats 250 to 380 micrometers (10 to 15 mils) thick, but coats of more conventional thickness are used to avoid shrinkage, solvent entrapment, cracks, and loss of adhesion. Two-part epoxy coatings have also been formulated in water-thinned systems. A waterborne epoxy primer for steel is described in SSPC-Paint 28 and a waterborne epoxy for cementitious substrates is described in SSPC-Paint 37.
6.10 STEEL JOIST SHOP PAINTING SYSTEM (SSPC-PS 14.01): This painting system is intended as a one-coat shop paint for open web and long span steel joists that may be either enclosed or exposed in the interiors of buildings where the temperature rarely falls below the dew point, where the relative humidity rarely exceeds 85 percent, and where corrosive protection is not necessary. This system is also used for temporary protection during delivery and erection.
6.11 CHLORINATED RUBBER PAINTING SYSTEMS (NO. 15)
6.11.1 Use: Chlorinated rubber coatings are quick-drying heavy-duty coatings with excellent chemical resistance to acids, alkalis, and water. They were used in maintenance and marine coating systems because they can be applied over wide ranges of temperature and humidity which allows application work to continue winter and summer. Regulations limiting solvent emission have led to the virtual elimination of chlorinated rubber systems on steel structures.
6.11.2 Description: In the chlorination process, isoprene reacts with chlorine to yield a product having 63 to 67 weight percent chlorine. In this polymer all double bonds are saturated with chlorine providing the material with optimum compatibility, stability, and fire resistance.
Chlorinated rubber is a tough film former. Ordinarily it is plasticized to become more flexible and adherent to steel. Formulations based on chlorinated rubber and chlorinated modifiers have been developed to provide systems that provide superior resistance to acids, alkalis, salt solutions, fresh water, and sea water. Generally, chemical resistance improves at low plasticizer levels. These coating systems are not resistant to aromatic or oxygenated solvents and to temperatures above 70°C (160°F).
A guide for selecting chlorinated rubber painting systems is described in SSPC-PS Guide 15.00. Typical formulas are described in SSPC-Paints 17, 18, and 19. The paints are applied as three-coat systems with the primer usually applied immediately after blast cleaning. Based on solvent selection, it is possible to apply three coats within 24 hours. Recoatability is never a problem when aged paint is free of oil, dirt, and chalk, since newly applied coats interact with aged chlorinated rubber films and form a monolithic film.
When using chlorinated rubber coatings, a wide range of solvent selection is available. Exceptions are alcohols, aliphatic hydrocarbons, and water. Care is necessary in selecting the proper solvent blend to meet variables such as weather conditions or type of application (conventional or airless spray, brush or roller), and government restrictions.
6.12 SILICONE-ALKYD PAINTING SYSTEM (SSPC-PS 16.01)
6.12.1 Use: The silicone alkyd painting system is used for new structural steel surfaces in industrial, rural, or marine atmospheres. The silicone alkyd finish coat is applied over an alkyd primer and an alkyd intermediate coat. This painting system can replace alkyd painting systems, with the advantage of superior exterior weatherability and minimum film erosion as shown by chalk resistance, gloss retention, and color retention. The painting system is acceptable for steel surfaces that will be exposed to the weather, high humidity, infrequent immersion, mild chemical atmospheres, and high temperature.
6.12.2 Description: The silicone alkyd painting system consists of three coats. The primer and intermediate coat are used with available organic paint systems. The finish coat is the silicone alkyd paint (SSPC-Paint 21), either high gloss (Type I) or medium gloss (Type II). A range of colors is available.
Silicone modification of the alkyd resin significantly improves its overall weatherability. The inertness of silicones, coupled with their moisture resistance, produces air-drying silicone alkyd copolymer resins which provide excellent durability because of their resistance to chalking which limits the rate at which film erosion takes place.
Extended tests on paint panels exposed in Florida at 45° south have shown that coatings containing 25 to 30 percent silicone intermediate resist chalking for up to three years. Non-silicone coatings weathered along with the silicone alkyd copolymer coatings chalked rapidly in comparison.
The advantages of coating systems that resist chalking are obvious. First, colored finishes will retain their initial appearance for a longer period of time and will not appear washed out and faded. Secondly, as previously mentioned, non-chalking finishes retain initial film thickness longer. Since a specific thickness of film protects the substrate, a coating that retains its film integrity will protect against corrosion for a longer period of time.
Silicone alkyd copolymer resins have the same general physical properties as conventional alkyd resins. Coatings can be applied in the usual manner by either brushing or spraying and require no unusual surface preparation. The same types of primers used for conventional alkyds should be used for silicone alkyds, since the main function of the silicone content is to provide final-coat protection from direct weathering.
The current applications of silicone modified alkyd paints include outdoor storage tanks, ships, chemical process equipment, buildings, bridges, and many other steel structures where improved film life and exterior weatherability are required.
6.13 URETHANE PAINTING SYSTEMS (SSPC-PS GUIDE 17.00)
6.13.1 Use: Urethanes and polyurethanes are made from isocyanates. Both uses and costs vary widely. Urethane coatings are currently being used successfully for maintenance of chemical plants, tankers, storage tanks, ships, and as exterior architectural varnishes.
6.13.2 Description: Coatings made from isocyanates are sometimes known as polyurethanes or urethanes. They are formed by reaction between an isocyanate (RNCO) and a hydroxy compound (ROM) to form a urethane RNHCOOR. If polyfunctional compounds are used, useful polyurethanes are formed, and some of these find applications as surface coatings.
The properties of this class of materials can be varied more widely than almost any other general class of polymer, since the hydroxy-containing reactant may be a drying oil, a non-drying oil, or a resin of the polyester, polyether, polyamine, polyamide, polyol, or other type. There are also several types of polyisocyanate that can be reacted. The resulting properties of the coating may range from fast to slow curing, from hard to flexible to soft types, and from extremely chemical resistant to low chemical resistant types.
Single package urethane coatings are made by reacting the isocyanate group with a drying oil. This results in the familiar type of drying oil coating that contains a metallic soap drier and dries by oxidation of the drying oil. The oil-modified urethane oils have been considered similar to alkyd resins, but with faster drying time and better resistance to water, humidity, and abrasion. They are commonly called uralkyds.
Pre-polymer types of single package coating result when the isocyanate groups are partially pre-reacted. When the coating is applied, these products then harden by reaction of these groups with atmospheric moisture. A catalyst can also be reacted with this type to accelerate the cure at room temperature. Many variations are possible, but two-package pre-polymers usually have limited pot life after mixing, and the catalyst ratio must be closely controlled.
Pre-polymers based on castor oil have better general durability than the drying oil modified urethanes, but do not have the chemical and solvent resistance of the two-package catalyzed materials. Specific resistance properties, however, can be tailored by proper choice of composition.
In general, abrasion resistance, hardness, and impact resistance of the urethanes are outstanding. They are less sensitive than most coatings to high humidity during application, but the single-package pre-polymers, which cure by reaction with moisture, are retarded at relative humidities below 30 percent. Adhesion is good but special primers may be necessary for water immersion. For the catalyzed types, surface preparation by blast cleaning to white metal is usually recommended for applications to structural steel.
6.14 LATEX PAINTING SYSTEMS (SSPC-PS 18.01 AND SSPC-PS 24.00)
6.14.1Use:Latex painting systems are suitable for all zones except immersion and extreme chemical exposures. Painting system SSPC-PS 18.01 describes a latex system suitable for use on normally dry interior and exterior exposures, as well as high humidity or mild chemical atmospheres. Painting system SSPC-PS 24.00, however, is also applicable to industrial and marine exposures.
6.14.2 Description: Painting system SSPC-PS 18.01 requires commercial blast cleaning (SSPC-SP 6) or pickling (SSPC-SP 8). Some procurement documents may specify a higher degree of cleaning such as white metal blast cleaning ( SSPC-SP 5) or near-white blast cleaning (SSPC-SP 10). The three-coat painting system consists of SSPC-Paint 23, “Latex Primer for Steel Surfaces,” an intermediate coat (Paint 23 tinted for color contrast), and the finish coat of SSPC-Paint 24, “Latex, Semi-Gloss Exterior Topcoat.” The finish paint is semi-gloss, chalk resistant and allows for a choice of colors.
Unlike most other SSPC painting systems, SSPC-PS 24.00 is performance-based; that is, the system must pass a battery of laboratory and field tests. Three levels of performance are described. The first level is based on early rusting, salt fog resistance, and other laboratory tests. The second and third levels require test fence evaluations of 12 months and 36 months, respectively, in addition to the laboratory testing. The paints in this system must have maximum VOC content of 340 g/liter (2.8 lb/gal).
6.15 PAINTING SYSTEMS FOR SHIPS (NO. 19 THROUGH 22):These painting systems are intended primarily for steel vessels and floating structures exposed to fresh water or salt water, fouling waters, and the weather. These systems are also suitable for steel in marine installations or for hydraulic structures. Steel in marine service is abrasive blast cleaned to a minimum of commercial (SSPC-SP 6). The minimum surface preparation on U.S. Navy ships is near-white (SSPC-SP 10). In maintenance painting, where only small areas need to be cleaned, thorough hand or power tool cleaning may suffice.
The definitions of the ship areas are as follows: The bottom of the steel exterior extends from the keel to the light load line. The boottopping is the exterior of the hull from the light load line to the deep load line. The topside is the area above the deep load line exposed to weather. This includes the freeboard (DLL-Rail), weather decks, and superstructure.
6.16 THERMAL SPRAY METALLIC COATING SYSTEMS (SSPC-CS 23.00)
6.16.1 Use: 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,” was developed jointly by SSPC, the American Welding Society (AWS), and NACE International.
Coating systems consisting of thermally sprayed zinc, aluminum, or zinc/aluminum alloys are suitable for use on structures or parts thereof exposed in SSPC environmental zones 1A (interior, normally dry), 1B (exterior, normally dry), 2A (frequently wet by fresh water), and 2C (fresh water immersion). With proper sealing/topcoating, thermal spray coatings can also be used in zones 2B (frequently wet by salt water), 2D (salt water immersion), 3A (chemical, acidic), 3B (chemical, neutral), and 3C (chemical, alkaline).
6.16.2 Description:Thermal spraying is a process wherein finely divided metallic materials are deposited in a molten or semi-molten condition that solidifies to form a coating. The most common metals used in thermal spraying are zinc, aluminum, or 85%/15% zinc/aluminum alloy.
Surfaces to be sprayed should normally be blast cleaned to white metal (SSPC-SP 5) but in some cases near-white blast cleaning (SSPC-SP 10) is permissible. The abrasive used in the cleaning should produce a sharp angular surface profile. Shot or other abrasives producing a rounded surface profile are not recommended.
Typically, the metal coating is applied at a minimum of 150 micrometers (6 mils) for zinc and zinc alloys and at 100 micrometers (4 mils) for aluminum. Maximum thicknesses are 250 to 380 micrometers (10 to 15 mils). Thermal spray coatings are almost always sealed and frequently also topcoated.
6.17ALUMINUM EPOXY COATING SYSTEM, PERFORMANCE-BASED (SSPC-PS 26.00): This is a coating material specification that sets performance parameters that the coating system must meet. Unlike most other SSPC painting system specifications, PS 26.00 only describes the coating material. To be incorporated into a job specification, other parameters such as surface preparation and paint application must also be specified.
6.17.1 Use: Coating systems meeting this specification are suitable for exposures in environmental zones 1A (interior, normally dry), 1B (exterior, normally dry), 2A (frequently wet by fresh water, excluding immersion), 2B (frequently wet by salt water, excluding immersion), and 3B (chemical exposure, neutral).
6.17.2 Description: This specification covers the requirements for an ambient temperature cure, two-component aluminum pigmented epoxy coating that is intended for use as a single or multi- coat system on steel. The specified coating system is intended for application by brush, spray, or roller. Type I is for use over steel surfaces blast cleaned to SSPCSP 6 or better. Type II is for use over non-blast cleaned as well as blast cleaned steel surfaces, i.e., surfaces cleaned to SSPC-SP 2 or better.
This coating is typically based on a reactive oxirane (epoxy) functional resin with an amine or polyamide functional curing agent. The principal functional pigment is aluminum paste or flake powder.
6.18 ALKYD COATING SYSTEM, PERFORMANCE- BASED (SSPC-PS 27.00): This is a coating material specification that sets performance parameters that the coating system must meet. Unlike many other SSPC paint system specifications, PS 26.00 only describes the coating material. To be incorporated into a job specification, other parameters such as surface preparation and paint application must also be specified.
6.18.1 Uses: The coating system is suitable for exposure in Environmental Zones 1A (interior, normally dry), 1B (exterior, normally dry), 2A (frequently wet by fresh water, excluding immersion), 2B (frequently wet by salt water, excluding immersion).
6.18.2 Description: This specification covers the requirements for an air-drying solvent-based alkyd coating system consisting of two or more coats of alkyd intended for use over blast cleaned steel. The specification covers both the system and the individual coating requirements. This multi-coat alkyd coating system specification does not cover coating systems comprised of water-reducible alkyds.
The requirements are based primarily on the performance of the coating system. The coating system is classified as Type 1 (fast drying), Type 2 (medium drying), or Type 3 (slow drying). The coating system is classified according to the drying time (fast, medium, slow) of the slowest drying coating layer.
The finish coat is designated as flat, semigloss, or gloss in a painting system.