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Wiping or scrubbing the surface with rags or brushes wetted with solvent.

Spraying of the surface with solvent. The final spraying shall be done with clean solvent.

Vapor degreasing, using stabilized chlorinated hydrocarbon solvents.

Complete immersion in a tank or tanks of solvent. Emulsion cleaners or steam cleaning may be used in place of the methods above, provided that after treatment the surface shall be washed with hot water to remove detrimental residue.

Method B, hand cleaning.After oil, grease, soluble welding flux residues, or salts are removed by methods prescribed under Method A, loose mill scale, loose rust, and other detrimental foreign matter shall be removed by hand brushing, hand sanding, hand scraping, hand chipping, hand hammering, or other methods using hand impact tools, or by a combination of these methods.

All accessible weld flux and spatter shall be removed by hand scraping or by hand impact tools followed by wirebrushing.

Areas which will be inaccessible after assembly shall be cleaned before assembly.

All rivets, welds, corners, joints, and openings shall be properly cleaned. The steel wires of the wire brushes shall have sufficient rigidity to clean the surface, shall be kept free of excess foreign matter, and shall be discarded when they are no longer effective. Hand scrapers shall be kept sharp enough to be effective. The tools shall be operated in such a manner that no burrs or sharp ridges are left on the surface and no sharp cuts made into the steel.

After hand cleaning is completed, dust and other loose matter shall be removed from the surface. Detrimental amounts of grease or oil still present shall be spot cleaned with solvent.

Method C, power tool cleaning.After oil, grease, soluble welding flux residues, or salts are removed by the methods prescribed under Method A, loose mill scale, loose rust, weld flux, and spatter shall be removed with power wire brushes, power impact tools, power grinders, power sanders, or by any combination of these methods.

Power wire brushes shall be of the rotary cup type of suitable size for entering all accessible openings, angles, joints, and corners. The steel wires of such brushes shall have sufficient rigidity to clean the surface, shall be kept free of excess foreign matter, and shall be discarded when they are no longer effective.

Power impact tools shall include power-driven chipping or scaling hammers, rotary scalers, single or multiple piston scalers, or other similar impact cleaning tools. Cutting edges of all tools shall be kept in effective condition.

Sanding or abrasive materials used in power sanding shall be discarded when they become ineffective.

Rivet heads, cracks, crevices, lap joints, fillet welds, and re-entrant angles shall be cleaned by the use of power wirebrushes, sharp chisels used in chipping, or scaling ham ers, rotary grinders, or sanders, or by a combination of such tools.

All tools shall be operated in such a manner that no burrs or sharp ridges are left on the surface and no sharp cuts are made into the steel.

Areas inaccessible for cleaning by power tools but accessible for hand cleaning shall be cleaned by methods outlined under Method B.

After these cleaning operations are completed, dust and other loose matter shall be removed from the surface. If detrimental amount of grease or oil are still present, these areas shall be spot cleaned with solvent.

Method D, blast cleaning.After heavy deposits of oil, grease, soluble welding flux residues, or salts are removed by the methods prescribed under Method A, loose mill scale, rust-scale, and other foreign matter shall be removed and the entire surface thoroughly cleaned by blasting except that excessive rust-scale shall, preferably, be removed by impact tools, as prescribed under Methods B and C. Any of the following blast cleaning methods may be used:

Dry sandblasting, using compressed air blast nozzles and dry sand.

Wet or water-vapor sandblasting, using compressed air blast nozzles and water and sand.

Grit-blasting, using compressed air blast nozzles and grit made of crushed cast iron, malleable iron, steel, or other metals.

Shot blasting, using compressed air nozzles and castiron, malleable-iron, or steel pellets.

Closed, recirculating nozzle-blasting using compressed air or vacuum with any of the above named abrasives.

Grit-blasting using centrifugal wheels and grit made of crushed cast iron, malleable iron, steel, or other metals.

Shot-blasting, using centrifugal wheels and cast-iron, malleable-iron, or steel pellets.

Blast cleaning shall be performed with SAE No. S-330 shot or smaller, SAE No. C-25 grit or smaller, or dry sand passing through a 16 mesh sieve, U.S. Standard Sieve Series.

The surface, if dry blasted, shall be brushed with clean brushes made of hair, bristle, or fiber, or blown off with compressed air (from which detrimental oil and water have been removed), or cleaned by vacuum, for the purpose of removing any traces of blast products from the surface, and also for the removal of abrasive from pockets and corners.

The surface, if wet sandblasted, shall be cleaned by rinsing with fresh water to which sufficient corrosion inhibitor has been added to prevent rusting, or with fresh water followed immediately by an inhibitive treatment. This cleaning shall be supplemented by brushing, if necessary, to remove any residue.

The compressed air used for nozzle blasting shall be free of detrimental amounts of water or oil. Adequate separators and traps shall be provided.

Blast cleaning operations shall be done in such a manner that no damage is done to partially or entirely completed portions of the work.

The blast cleaned surface shall be examined for any traces of oil, grease, or smudges deposited in the cleaning operations. If present, they shall be removed as outlined under Method A. Cleaned surfaces will be approved by the Engineer prior to painting.

611.23 Schedule of Paint Coats for Metals. Steel structures shall be painted with not less than three coats of paint as specified below. The paint to be used for each coat shall be as shown on the plans or stipulated in the special provisions. (a) Primer coats :

(1) Red lead ready-mixed paint of the type shown on the plans or stipulated in the special provisions.

(2) Primer for galvanized metal: zinc dust-zinc oxide paint.

(3) Red lead-iron oxide paint.

(4) Basic lead silico-chromate orange primer. (b) First field coats :

(1) Red lead ready-mixed paint of the type shown on the plans or stipulated in the special provisions.

(2) White and tinted ready-mixed paint, class B, tinted light gray with lampblack.

(3) Red lead-iron oxide paint.

(4) Basic lead silico-chromate buff intermediate paint. (c) Second field coat:

(1) Aluminum paint.

(2) White and tinted ready-mixed paint, class B, tinted with lampblack to light gray of a different shade from that of the first field coat.

(3) Foliage green bridge paint.

(4) Basic lead silico-chromate green or gray finish. 611.24 Painting Metal Surfaces: (a) Time of application.—The prime coat of paint, or

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pretreatment when specified, shall be applied as possible after the surface has been cleaned and before deterioration of the surface occurs. Any oil, grease, soil, dust, or foreign matter deposited on the surface after the surface preparation is completed shall be removed prior to painting. In the event that rusting occurs after completion of the surface preparation, the surfaces shall be again cleaned.

Particular care shall be taken to prevent the contamination of cleaned surfaces with salts, acids, alkali, or other corrosive chemicals before the prime coat is applied and between applications of the remaining coats of paint. Such contaminants shall be removed from the surface. Under these circumstances, the pretreatments or, in the absence of a pretreatment, the prime coat of paint shall be applied immediately after the surface has been cleaned.

(b) Storage of paint and thinner.—All paint and thinner should preferably be stored in a separate building or room that is well ventilated and free from excessive heat, sparks, flame, or the direct rays of the sun. Paints susceptible to damage from freezing shall be kept in a heated storage space when necessary.

All containers of paint should remain unopened until required for use. Containers which have been opened shall be used first.

Paint which has livered, gelled, or otherwise deteriorated during storage shall not be used. Thixotropic materials which may be stirred to attain normal consistency are satisfactory.

(c) Mixing and thinning.All ingredients in any container of paint shall be thoroughly mixed before use and shall be agitated often enough during application to keep the pigment in suspension.

Paint mixed in the original container shall not be transferred until all settled pigment is incorporated into the vehicle. This does not imply that part of the vehicle cannot be poured off temporarily to simplify the mixing.

Mixing shall be by mechanical methods, except that hand mixing will be permitted for containers up to 5 gallons in size.

Mixing in open containers shall be done in a well ventilated area away from sparks or flames.

Paint shall not be mixed or kept in suspension by means of an air stream bubbling under the paint surface.

Where a skin has formed in the container, the skin shall be cut loose from the sides of the container, removed, and discarded. If such skins are thick enough to have a practical effect on the composition and quality of the paint, the paint shall not be used.

The paint shall be mixed in a manner which will insure

breaking up of all lumps, complete dispersion of settled pigment, and a uniform composition. If mixing is done by hand, most of the vehicle shall be poured off into a clean container. The pigment in the paint shall be lifted from the bottom of the container with a broad, flat paddle, lumps shall be broken up, and the pigment thoroughly mixed with the vehicle. The poured-off vehicle shall be returned to the paint with simultaneous stirring, or pouring repeatedly from one container to another until the composition is uniform. The bottom of the container shall be inspected for unmixed pigment.

Tinting pastes or colors shall be wetted with a small amount of thinner, vehicle, or paint and thoroughly mixed. The thinned mixture shall then be added to the large container of paint and mixed until the color is uniform.

Paint which does not have a limited pot life, or does not deteriorate on standing, may be mixed at any time before using, but if settling has occured it must be remixed immediately before using. Paint shall not remain in spray pots, painters' buckets, etc., overnight, but shall be gathered into a container and remixed before use.

No thinner shall be added to the paint unless necessary for proper application. In no case shall more than one pint of thinner be added per gallon unless the paint is intentionally formulated for greater thinning.

The type of thinner shall comply with the paint specification.

When the use of thinner is permissible, thinner shall be added to paint during the mixing process. Painters shall not add thinner to paint after it has been thinned to the correct consistency.

All thinning shall be done under supervision of one acquainted with the correct amount and type of thinner to be added to the paint. (d) Application of paint:

(1) General.—The oldest of each kind of paint shall be used first. Paint shall be applied by brushing or spraying or a combination of these methods. Daubers or sheepskins may be used when no other method is practicable for proper application in places of difficult access. Dipping, roller coating, or flow coating shall be used only when specifically authorized.

Open seams at contact surfaces of built up members which would retain moisture shall be caulked with red lead paste, or other approved material, before the second undercoat of paint is applied.

Paint shall not be applied when the surrounding air temperature is below 40° F. Paint shall not be applied when

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