SELECTION OF COATINGS

4.1 Available Guidance. Guidance for specifying coating systems for original or maintenance painting of shore facilities is found in specialized guide specifications such as NFGS-13283 or CEGS 09900 or in Air Force Engineering Technical Letters. In these documents, surface preparation for the primer is usually considered a part of the system because of its importance in system performance and is included in the guidance. Recommendations for coating systems are also available from an Army, Navy, or Air Force coatings specialist. These specialists are particularly helpful when criteria for a specialized job are not available or when guidance documents are out of date.

4.2 Selection Criteria. The best selection of a coating system for a particular service is determined by a variety of factors. These include desired properties, work requirements and limitations, safety and environmental restrictions, compatibilities, and costs.

4.2.1 Desired Film Properties. In selecting a coating system, the first consideration is the desired properties of the system for the particular service. Desired properties may include one or more of the following aspects:

a) Resistance to exterior weathering (chalking; color and gloss retention)

b) Water, fuel, or chemical resistance

c) Abrasion, heat or mildew resistance

d) Appearance (color, gloss, and texture)

e) Drying time

f) Ease of application and maintenance

4.2.2 Work Requirements or Limitations. The following work requirements or limitations may have to be considered:

a) Type of surface preparation

b) Access to work

c) Drying times

d) Necessary applicator skills

e) Necessary equipment

f) Scaffolding for access to work

4.2.3 Safety and Environmental Restrictions. It will be necessary to conform to all prevailing safety and environmental regulations concerning materials and processes to be used for surface preparation and for coating application. These regulations are discussed more fully in Section 3 of this handbook.

4.2.4 Compatibilities. Coating systems must be compatible with the surfaces to which they are applied. Coating incompatibility can cause failures at or just after application or after a much longer time. Failures occurring just after application are due to solvent incompatibility or wetting problems. Failures associated with slow chemical reactions, such as those occurring between alkaline surfaces (e. g., concrete and galvanized steel) and oil-based paints or mechanical property mismatches (e. g., a rigid coating applied over a more flexible one) cause failure in a longer timeframe. The failure more often is peeling. For existing coatings being repainted, compatibility generally means that topcoats should be of the same generic type or curing mechanism as undercoats. One exception to this rule is inorganic zinc coatings. Since inorganic zinc coatings frequently do not bond well to themselves, it is safest to repair them with zinc-rich organic coatings.

A simple test to classify coatings is to determine solvent sensitivity using an methylethyl ketone (MEK) or acetone rub test. To do this, soak a cloth in MEK or acetone, rub it against the existing paint, and visually check for pick up of paint. The paint is classified as "solvent soluble" if paint is picked up, and as "solvent insoluble" if not.

Another practical method of ensuring topcoat solvent compatibility is to coat a small test area of the existing coating with the paint selected for the work. If situations permit, this test is preferred over the MEK rub test because it is specific for the surface to be repainted. The test area should be visually inspected the following day (or preferably after 3 or more days) for bleeding of undercoat, wrinkling, loss of adhesion, or other coating defects. Although most incompatibility problems are apparent in a couple of days, some types of incompatibility may not become apparent for several months or until after a change of seasons. These types are usually associated with mechanical film properties.

4.2.5 Costs. Life cycle cost has always been one of the most important considerations in selection of coating systems. Life cycle costs include original surface preparation, materials, and application and necessary maintenance throughout the life of the

coating system. Today, the expense of containment of old paint during its removal and disposal of debris that is often considered to constitute hazardous waste must be included. This usually means that the system with the maximum maintainable life is the best choice.

4.3 Specifications for Lead – and Chromate-Free Coatings

With VOC Limits. The coating specifications listed below in Table 5 are lead – and chromate-free and have limitations on their contents of VOC.

Table 5

Lead – and Chromate-Free Coating Specifications With VOC Limits

Latex Coatings

Listed latex coatings are available with a VOC content of no more than 250 grams per liter unless otherwise specified

TT-P-19

Exterior acrylic emulsion coating, available in a wide variety of colors and flat gloss finishes

TT-P-29

Interior latex paint, flat, available in white and tints

TT-P-650

Interior latex primer coating for gypsum board or plaster

TT-P-1510

Latex exterior flat finish coating, available in a variety of colors

TT-P-1511

Latex interior coating, available in gloss and semigloss in white and tints

TT-P-1728

Latex, interior, flat, deep-tone coating

TT-P-001984

Primer, latex, for wood

TT-P-002119

Latex high-traffic coating, available in flat and eggshell and a variety of colors

TT-E-2784

Acrylic emulsion exterior enamel, gloss and semigloss, available in a wide variety of colors

MIL-E-24763

Acrylic water-emulsion coating intended for shipboard use, available in 275 and 340 grams per liter VOC classes; high, medium, low, and flat glosses; and a limited number of colors

MIL-P-28577

Corrosion-resistant latex primer for metals

Stains

MIL-P-28578

Waterborne acrylic semigloss finish, available in a wide variety of colors

TT-S-001992

Exterior latex stain, semi-transparent and opaque, available in a variety of colors

Clear Floor Finishes

A variety of clear floor finishes are available from the Maple Flooring Manufacturers Association (MFMA) specifications, Heavy-Duty and Gymnasium Finishes forMaple, Beech, and Birch Floors. Suppliers on the attached

list must be contacted to determine VOC content.

Oil and Alkyd Coatings

SSPC PAINT-25

Corrosion-resistant raw linseed oil and alkyd primer, usually available at 300 grams per liter VOC but no requirement listed

Table 5 (Continued)

Lead – and Chromate-Free Coating Specifications With VOC Limits

TT-P-25

Oil-based primer for wood, normally available with a VOC content less than 350 grams per liter

TT-P-31

Red and brown oil ("roof and barn") paint, usually available with 250 grams per liter VOC content but no requirement specified

TT-E-489

Alkyd enamel, with 420 grams per liter VOC limitation, available only in gloss, but in a wide variety of colors

TT-P-645

Corrosion-resistant alkyd primer, with a 340 VOC limitation

TT-P-664

Corrosion-inhibiting alkyd quick-dry primer, with a 420 grams per liter VOC limitation

MIL-E-24635

Silicone alkyd enamel, available in limited colors, 275, 340, and 420 grams per liter VOC types, and high, medium, low, and flat gloss classes

MIL-P-28582

Alkyd primer normally available at less than 350 grams per liter

Epoxy Coatings

MIL-P-24441

Epoxy-polyamide, two – and three-coat systems, available in types with 340 VOC and limited colors

MIL-P-53022

Fast-dry epoxy primer with 420 grams per liter maximum VOC content

MIL-P-85582

Waterborne epoxy primer with 340 grams per liter maximum VOC content

Textured Coatings

TT-C-555

Waterborne or oil – or rubber-based textured coating available at 250 grams per liter

Urethane Coatings

MIL-C-85285

High-solids aliphatic urethane coating, with 340 and 420 grams per liter VOC types, available in a variety of colors and in glass and semigloss

Zinc-Rich Coatings

MIL-P-24648

Zinc-rich coating, aqueous and organic solvent types, self-curing and post-curing classes, organic and inorganic vehicles, with 340 grams per liter maximum VOC content

4.4 Recommendations for Different Substrates. This portion

of Section 4 provides general recommendations for wood, concrete and masonry, steel, galvanized steel, and aluminum surfaces. The recommended dft in mils is provided for coating specification recommended for a particular substrate. More detailed recommendations for coating particular structures are presented in Section 5 of this handbook. Referenced standards for coatings provide for lead – and chromate-free products that are low in VOCs. Although such requirements may not be necessary at all activities, such requirements may occur in the near future.

In making local repairs of damaged coatings, loose paint should be removed by scraping with a putty knife before lightly sanding or abrasive blasting any exposed substrate and feather-edging existing sound paint to obtain a smooth transition with the repaired area. Coats of repair material should be extended 1 inch onto the surrounding sound coating.

4.4.1 Recommendations for Wood. Oil-based and waterborne coatings and stains (frequently called latex) perform quite well on new wood. A two-coat system, paint or stain, is normally applied. However, as additional coats are applied to resurface or repair weathered paint, the film thickness may become sufficient to reduce the total flexibility to the point that results in disbonding of the total paint system from the surface. Thus, when topcoating or making localized repairs, no more coating should be applied than necessary to accomplish the desired goal.

Surface preparation of new wood normally consists of lightly hand sanding or power sanding, carefully controlled so that it does not damage the wood. Sanding is also appropriate for preparing weathered surfaces for refinishing and for spot repairing areas of localized damage.

4.4.1.1 Oil-Based Paints. Historically, wood has been successfully painted with oil-based products that penetrate the surface well. These coatings are very easy to apply.

Oil-Based Paint System for Wood

Surface

Preparation Primer Topcoat

Sand one coat TT-P-25 or one-two coats MIL-E-24635

MIL-P-28582 or TT-P-102

2 mils dft 2 mils dft per coat

4.4.1.2 Water-Emulsion Paints. More recently, latex coatings have been found to be very effective in providing attractive, protective finishes. They are also less affected by moisture than are oil-based finishes and are generally more flexible and thus less susceptible to cracking as the wood swells and contracts with moisture changes.

A problem sometimes arises when repairing or topcoating existing smooth alkyd coatings with latex paints. To obtain good intercoat adhesion, it may be necessary to lightly sand the existing paint and/or apply a surface conditioner containing tung oil or some other oil that wets surfaces well before applying the first coat of latex paint.

Surface

Preparation Primer Topcoat

Sand one coat TT-P-001984 one-two coats TT-E-2784

1.5 mils dft or other appropriate

latex paint in Table 5

1.5 mils dft per coat

4.4.1.3 Semi-Transparent Stains. Because oil-based and waterborne paints form continuous films, they may form blisters or disbond because of moisture in the wood attempting to escape. Semi-transparent stains do not form continuous films on wood and so do not have this problem. Thus, they are a good alternative on new wood. Additional coats applied over the years or heavy­bodied stains will, however, form continuous films.

Stains for Wood

Surface

Preparation Primer Topcoat

Sand one coat TT-S-001992 one coat TT-S-001992

1.5 mils dft 1.5 mils dft

4.4.1.4 Clear Floor Finishes. A variety of clear floor finishes are available from MFMA Heavy-Duty and Gymnasium Finishes for Maple, Beech, and Birch Floors. Suppliers on the attached list must be contacted to determine VOC content.

Surface preparation for hard wood floors is described in detail in NFGS-13283 or CEGS 09900.

4.4.2 Recommendations for Concrete and Masonry Surfaces.

Concrete and masonry surfaces, as well as those of stucco, plaster, wallboard, and brick, can be coated with a variety of systems depending upon the desired purpose and appearance.

Surface preparation is usually accomplished by power washing with aqueous detergent solution to remove dirt and other loose materials. Any oil or grease will have to be removed by solvent or steam cleaning; any mildew, by scrubbing with bleach; and any efflorescence or laitance, by brushing, followed by acid treatment. These techniques are described more fully in Section 6.

4.4.2.1 Waterborne Coatings. A two-coat waterborne (latex) system provides an attractive breathing film that is normally less affected by moisture in the concrete than non-breathing systems. The latex material is a self-primer in this service,

unless otherwise stated. Alkyd and other oil-based coatings should not be applied directly to concrete or masonry surfaces, because the alkalinity in the concrete will hydrolyze the oil in the binder and cause the coating to peel. However, they can be applied over concrete or masonry surfaces primed with waterborne coatings to produce a tougher, more washable finish.

Waterborne Coating System for Concrete/Masonry

Surface

Preparation Primer/Topcoat

Power wash two coats of TT-E-2784 or other

appropriate* waterborne coating

1.5 mils dft each coat

*Interior or exterior product, desired gloss and color available. TT-P-29 is less expensive and normally used on interior surfaces.

4.4.2.2 Elastomeric Coatings. Elastomeric, waterborne acrylic coating systems also perform well to seal and protect concrete/masonry surfaces and are normally very low in VOCs.

They can successfully bridge fine or larger caulked cracks.

There are no Government or military specifications for them.

Elastomeric Waterborne Acrylic System for Concrete or Masonry

Surface

Preparation Primer Topcoat

Подпись:Подпись:one coat primer recommended by supplier of elastomeric coating dft varies with supplier

4.4.2.3 Textured Coatings. Textured coatings system can bridge fine cracks and waterproof from wind-driven rain. They are normally applied over a primer recommended by the supplier to insure good adhesion. They are available in a variety of textures and may be waterborne or oil or rubber-based products with a VOC limit of 250 grams per liter.

Surface

Preparation

Primer

Topcoat

Power wash

one coat primer recommended one coat TT – by supplier of textured 20 – 30 mils coating dft varies with supplier

C-555

dft

4.4.2.4 Epoxy Coatings. A two-coat epoxy system will seal and protect concrete/masonry surfaces well. An aliphatic urethane finish coat should be used rather than the second epoxy coat on exterior surfaces to improve the weatherability.

Exterior

Epoxy/Urethane System for Concrete or Masonry

Surface

Preparation

Primer

Topcoat

Power wash

one coat MIL-P-24441 Formula 15 3 mils dft

MIL-C-85285 Type II 2 mils dft

Interior Epoxy System for Concrete or Masonry

Surface

Подпись:

SELECTION OF COATINGS

Preparation Primer Topcoat

4.4.3 Recommendations for Steel. Presently, a high-

performance coating system is recommended to prolong the service before it becomes necessary to remove and replace it. Costs in coating removal, especially where there are restrictions on abrasive blasting, are very high.

Abrasive blasting is always preferred to alternative methods of preparing steel surfaces for painting. It cleans the steel and provides a textured surface to promote good primer adhesion. A commercial blast (SSPC SP 6) is normally adequate for alkyd and epoxy primers for a moderate environment. A near­white blast (SSPC SP 10) is required for epoxies, including zinc – rich epoxies, exposed to a severe environment such as marine atmospheric or water or fuel immersion. Some manufacturers may specify a white metal blast (SSPC SP 5) for particular coatings for special applications. It is important that a contract specification does not conflict with the coating manufacturer’s
written directions. A white metal blast (SSPC SP 5) is recommended for zinc-rich inorganic primers. If abrasive blasting cannot be done, then power tool cleaning to bare metal (SSPC SP 11) is recommended. It provides a surface cleanliness and texture comparable to those of a commercial blast (SSPC SP 6). Hand tool cleaning (SSPC SP 2) or power tool cleaning, however, may be adequate in making localized repairs.

4.4.3.1 Alkyd Systems. In the past, most military steel structures with atmospheric exposures were coated with an alkyd or other oil-based system. Three-coat alkyd systems provided adequate protection in moderate atmospheric service. On new painting, they are being replaced in significant part by epoxy systems that provide longer protection. Alkyd systems, however, will still be used in large volume for repairing old deteriorated alkyd systems.

Подпись: Surface Preparation Подпись: SSPC SP 6

SELECTION OF COATINGS

Alkyd Coating System for Steel

4.4.3.2 Epoxy Coating Systems. A three-coat epoxy system provides good interior service in harsh as well as moderate environments. An aliphatic urethane finish system is used in place of the third epoxy coat in exterior service to provide greater resistance to deterioration by ultraviolet light.

Several different epoxy mastic systems, some aluminum-filled, have been used successfully on steel structures. However, there is no specification for one at this time.

Подпись: Surface Preparation Подпись: Primer/Mid Coat Подпись: Topcoat

Подпись: SSPC SP 6 or 10 one coat each MIL-P-24441

SELECTION OF COATINGS

Epoxy System for Exterior Steel

Surface

Preparation Primer/Mid Coat Topcoat

Подпись:SSPC SP 6 or 10 one coat each MIL-P-24441

Formulas 150 and 151 3 mils dft per coat

4.4.3.3 Zinc-Rich Coatings. Good protection from corrosion and abrasion can be provided by zinc-rich inorganic coatings. They perform well untopcoated in a variety of environments except acidic or alkaline. They may be topcoated with an acrylic latex finish coat to provide a variety of color finishes. Epoxy (for interior) or epoxy and aliphatic urethane (for exterior) topcoats may also be used. Localized repair of inorganic zinc systems is usually accomplished with a zinc-rich organic coating to permit good bonding to any exposed steel, inorganic coating, or organic topcoats.

Zinc-Rich System for Steel

Surface

Preparation Primer Topcoat

Подпись:Подпись: None, or one or more coats of acrylic or latex, epoxy, etc.1-MIL-P-24648 Composition B (inorganic), 3 mil dft (Composition A (organic) can be used when a more "forgiving" system is needed, refer to pars. 2.3.8 and 2.3.9

4.4.4 Recommendations for Galvanized Steel. Galvanized steel

corrodes very slowly in moderate environments but may be painted with organic coating systems to provide color or additional corrosion protection, particularly in severe environments. It should never be coated directly with an alkyd paint, because the alkalinity on the surface of the galvanizing will hydrolyze the oil in the binder, degrading the binder, and cause paint peeling.

New galvanizing should be solvent or steam cleaned (SSPC SP 1, Solvent Cleaning) to remove any grease or oil before coating. Older, untopcoated galvanizing should be power washed to remove any dirt or loose zinc corrosion products. Any loose coatings should also be removed by power washing or scraping and sanding to produce a clean, sound surface. Rust should be removed by waterblasting or careful abrasive blasting to limit the removal of galvanizing.

4.4.4.1 Epoxy Systems. Two coats of epoxy will provide long­term protection to galvanizing in interior service, as will one coat of epoxy and one coat of aliphatic urethane to galvanizing in exterior service.

Epoxy Coating System for Exterior Galvanizing

Surface

Preparation Primer Topcoat

SSPC SP 1 one coat MIL-P-24441 one coat MIL-C-85285

Formula 150 Type II

3 mils dft 2 mils dft

Epoxy Coating System for Interior Galvanizing

Surface

Preparation Primer Topcoat

SSPC SP 1 one coat MIL-P-24441 one coat MIL-P-24441

Formula 150 of desired color

3 mils dft 3 mils dft

4.4.4.2 Waterborne System for Galvanizing. Two coats of latex paint will provide a pleasing appearance and good protection to galvanized steel in moderate environments. They are easy to apply.

Waterborne Coating System for Galvanizing in Moderate Environment Surface

Preparation Primer Topcoat

SSPC SP 1 one coat TT-E-2784 one coat TT-E-2784 *

1.5 mils dft 1.5 mils dft

* Other commercially available acrylic latex systems will also perform well.

4.4.5 Recommendations for Aluminum. Aluminum surfaces

corrode very slowly in moderate environments. They may be coated to provide color or additional protection, particularly in severe environments. Epoxy and epoxy/urethane systems perform well in interior or exterior service, respectively. Alkyd systems usually require surface pretreatments containing toxic materials.

Because aluminum surfaces are relatively soft, they should not be cleaned by blasting with conventional abrasives or grinding to avoid damage. Any grease or oil should be removed by solvent or steam cleaning (SSPC SP 1). Dirt and other loose

contaminants should be removed by power washing. Existing coatings are best removed by careful blasting with a soft abrasive (e. g., plastic). Alkaline strippers should never be used, because they will attack the aluminum.

Coating System for Aluminum

Surface

Preparation

Primer Topcoat

See above

one coat MIL-P-24441 one-two coats Formula 150 or MIL-C-85285 Type II MIL-P-53022 2 mils per coat 3 mils