The Language of Finishing: Paint and Coatings Glossary R

This installment of the AirSprayTech.com Paint and Coatings Industry Glossary covers terms beginning with the letter R. These definitions address coating application, surface preparation, repair, respiratory protection, roof coatings, spray equipment, quality control, corrosion, and common coating defects.

Coating terminology can have different meanings depending on the industry, specification, manufacturer, or application process. Always consult the governing specification, approved product data sheet, safety data sheet, equipment manual, and complete referenced standard before performing coating work.

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R

RAL Color System

RAL is a standardized color-matching system widely used for industrial coatings, powder coatings, architectural components, machinery, transportation equipment, and manufactured products.

A RAL number identifies a color standard, but the final appearance can still be influenced by gloss, texture, coating chemistry, substrate color, film thickness, cure, application method, lighting, and viewing angle.

Color approval should use the correct RAL collection and, when appearance is critical, an approved physical sample. Information about the system is available from RAL Colours.

Ratio

Ratio describes the proportional relationship between two or more quantities. In the coatings industry, it may refer to a coating mix ratio, pump pressure ratio, catalyst ratio, air-to-fluid relationship, or proportioning equipment setting.

The type of ratio must be identified. A four-to-one coating ratio by volume is not necessarily equivalent to four-to-one by weight. A pump pressure ratio describes potential pressure multiplication and does not describe the coating mix ratio.

Raw Edge

A raw edge is an exposed, uncoated, freshly cut, or otherwise untreated edge of a substrate. Raw edges may occur after cutting, drilling, trimming, machining, or assembling a previously coated component.

These areas can become early corrosion sites because the protective coating or pretreatment has been interrupted. The repair procedure should address cleaning, edge preparation, compatible primer, and restoration of the required coating thickness.

Reach

In spray application, reach describes the practical distance or access capability of the applicator and equipment. Pole guns, extension nozzles, angled tips, remote manifolds, and specialized applicators may be used to reach ceilings, structural members, tanks, pipes, recesses, or confined areas.

Increasing physical reach does not eliminate the need to maintain correct spray distance and gun angle. Excessively long extensions can also affect balance, triggering, pressure drop, grounding, and operator control.

Rebound

Rebound is coating, powder, or abrasive material that strikes the target and bounces away instead of remaining on the surface.

In liquid spraying, rebound may increase with excessive atomizing pressure or air velocity. In powder coating, poor grounding, excessive powder output, excessive voltage, or a heavily insulated film may contribute. In abrasive blasting, rebound is a normal hazard that must be controlled through protective equipment and containment.

Recoat

To recoat means to apply an additional coating layer over a previously applied coating. The new layer may be part of the original system, a repair, a maintenance coat, or a complete overcoat.

Before recoating, the applicator must verify that the existing film is sufficiently cured, clean, dry, compatible, and within the permitted recoat window. Additional washing, abrading, or application of a tie coat may be required.

Recoat Interval

The recoat interval is the period that must pass, or is permitted to pass, between coating layers under stated conditions.

A product data sheet may identify a minimum recoat time, maximum recoat time, or both. The actual interval is often affected by surface temperature, humidity, ventilation, film thickness, coating chemistry, and exposure to sunlight or contamination.

A coating that feels dry may not have reached its minimum recoat time. Likewise, a coating that appears clean and sound may have exceeded its maximum interval and require additional preparation.

Recoat Window

The recoat window is the range of time during which another coating layer may be applied without a special surface-treatment procedure.

Recoating too early may trap solvent or moisture, disturb the film, or interfere with cure. Recoating too late may result in poor intercoat adhesion because the existing coating has become too hard, smooth, weathered, or chemically resistant.

If the recoat window has been exceeded, follow the coating manufacturer’s approved procedure. This may involve cleaning, abrasion, solvent wiping, or use of a compatible tie coat.

Recovery Efficiency

Recovery efficiency is the percentage of oversprayed coating material successfully collected by a recovery or collection system.

In powder coating, recovered powder may be returned to the application process when the product, color, and quality requirements permit. Recovery efficiency should not be confused with transfer efficiency, which measures the amount of material deposited on the workpiece.

Recycled Powder

Recycled powder is oversprayed powder collected and returned to the application process. It is also called reclaimed powder.

Recovered powder may differ from virgin powder because of contamination, particle-size separation, moisture, heat exposure, or repeated circulation. A controlled blend of virgin and reclaimed powder may be needed to maintain consistent charging, flow, color, texture, and film build.

Reducer

A reducer is a liquid added to a coating to adjust viscosity, flow, atomization, evaporation rate, or application characteristics. The words reducer and thinner are sometimes used interchangeably, although manufacturers may assign them different meanings.

Only the type and quantity permitted by the coating manufacturer should be used. An incorrect reducer can cause lifting, slow cure, dry spray, solvent popping, poor leveling, gloss loss, color change, or reduced film performance.

Reduction

Reduction is the process of adding an approved reducer, thinner, water, or other permitted liquid to adjust a coating for application.

Reduction changes more than viscosity. It can affect wet-film thickness, volume solids after mixing, coverage, sag resistance, drying, atomization, emissions, and the amount of material needed to achieve the specified dry-film thickness.

The amount added should be measured and recorded. Informal instructions such as “thin as needed” should be replaced by a controlled procedure whenever quality or regulatory compliance is important.

Reference Standard

A reference standard is an authoritative document, photograph, comparator, test panel, instrument standard, or approved sample used to establish a requirement or evaluate results.

Examples include written ASTM or AMPP standards, ISO visual-cleanliness photographs, surface-profile comparators, color standards, gloss standards, and approved appearance panels.

The exact designation, revision, method, and acceptance criterion should be identified. A standard’s title alone may not provide enough information to perform the work correctly.

Relative Humidity — RH

Relative humidity is the amount of water vapor present in air compared with the maximum amount the air could hold at the same temperature, expressed as a percentage.

Relative humidity affects condensation risk, solvent and water evaporation, coating cure, abrasive condition, static electricity, and application of moisture-sensitive materials.

RH must be evaluated together with air temperature, surface temperature, and dew point. A low relative humidity does not by itself prove that a surface is safely above the dew point.

Repair

A coating repair is localized work performed to correct a defect, restore damaged film, or bring a nonconforming area into compliance.

Repairs may address holidays, pinholes, low thickness, runs, mechanical damage, corrosion, poor adhesion, contamination, weld areas, or damage caused by inspection testing.

A repair procedure should define removal of unsound material, surface preparation, feathering, cleaning, approved repair coating, overlap onto sound film, required thickness, cure, and reinspection.

Repair Area

A repair area is the portion of a coated surface that has been identified for corrective work. It should include not only the visible defect but also any surrounding coating that is loose, undercut, contaminated, weakly adhered, or otherwise unsuitable.

Repair boundaries should be clearly marked and documented. Abrupt edges may require feathering to produce a sound transition between the existing coating and repair material.

Repair Coat

A repair coat is a coating layer applied to restore protection or appearance in a damaged or nonconforming area. It may be the same product used in the original system or a manufacturer-approved alternative.

The repair coating must be compatible with the exposed substrate, remaining coating, service environment, and future coats. A convenient aerosol or maintenance paint should not be substituted without technical approval.

Replica Tape

Replica tape is a compressible tape used to create a reverse impression of a prepared surface profile. The tape is pressed against the surface with a burnishing tool and then measured with a suitable micrometer.

The measurement procedure accounts for the thickness of the tape’s noncompressible backing. Tape grade must be appropriate for the expected profile range, and the instrument should be verified before use.

Replica tape is one of the field methods addressed by ASTM D4417, Field Measurement of Surface Profile of Blast-Cleaned Steel.

Resin

Resin is the film-forming portion of a coating binder. It helps determine adhesion, flexibility, hardness, chemical resistance, weathering, gloss retention, and curing characteristics.

Common resin families include acrylic, alkyd, epoxy, polyester, polyurethane, silicone, vinyl, and fluoropolymer technologies.

The general resin name does not completely define coating performance. Products within the same resin family can have very different application requirements and service capabilities.

Respirator

A respirator is personal protective equipment designed to reduce inhalation of specified airborne contaminants. Types include filtering facepiece respirators, elastomeric air-purifying respirators, powered air-purifying respirators, supplied-air respirators, and self-contained breathing apparatus.

Respirator selection depends on the contaminant, concentration, exposure limit, oxygen level, work activity, assigned protection factor, cartridge or filter limitations, and emergency conditions.

When respirators are required, employers must establish an appropriate respiratory-protection program. This can include medical evaluation, fit testing, training, equipment inspection, cleaning, storage, cartridge-change schedules, and program evaluation.

Current requirements and guidance are available from OSHA’s Respiratory Protection resources.

Respiratory Protection Program

A respiratory protection program is the organized system used to select, provide, maintain, and manage respirators when workplace exposures require them.

The program should be based on a qualified hazard evaluation and address respirator selection, medical evaluation, fit testing, training, inspection, maintenance, storage, breathing-air quality where applicable, cartridge change schedules, and recordkeeping.

A dust mask or cartridge respirator should never be selected solely because it is convenient or already available.

Retardant

A retardant is a material or coating component that slows a process. Depending on the context, it may slow drying, curing, flame spread, corrosion, or another reaction.

A retarder added to a coating may slow solvent evaporation and improve flow under hot or dry conditions. Excessive use can cause slow drying, runs, solvent entrapment, contamination pickup, or changes in appearance.

Retarder

A retarder is a slow-evaporating reducer or additive used to extend wet-edge time, improve leveling, reduce dry spray, or control defects caused by evaporation that is too rapid.

Retarders are commonly used in lacquer, automotive, wood-finishing, and industrial spray applications. Only an approved product should be used, and the quantity must remain within the manufacturer’s instructions.

Reverse-Impact Test

A reverse-impact test evaluates a coating’s ability to remain attached while the test panel is rapidly deformed from the uncoated side. The deformation forces the coating on the opposite side to stretch.

The test can reveal brittleness, cracking, or loss of adhesion that may not appear during direct impact. Results depend on the substrate, coating thickness, cure, impact energy, test equipment, and evaluation method.

A commonly referenced method is ASTM D2794, Resistance of Organic Coatings to Rapid Deformation.

Rinse

Rinsing uses water or another approved liquid to remove cleaner, chemicals, salts, residue, loose contamination, or reaction products from a surface.

Rinse-water quality can strongly affect the final surface. Hardness, dissolved salts, conductivity, pH, temperature, contamination, and water replacement rate may require control.

Insufficient rinsing can leave residues that interfere with coating adhesion or promote osmotic blistering. The surface should also be protected from contamination and flash rust after rinsing.

Rinse Water

Rinse water is the water used to remove cleaning chemicals, pretreatment residues, salts, dirt, and loosened contamination from a substrate or production part.

Depending on the process, rinse water may be potable, softened, deionized, reverse-osmosis-treated, or otherwise controlled. The required quality becomes more critical in final rinses and high-performance OEM finishing.

Rising Moisture

Rising moisture is the upward movement of water or water vapor through concrete, masonry, or another porous substrate. It may result from capillary movement, ground moisture, hydrostatic pressure, or vapor transmission.

Rising moisture can contribute to blistering, efflorescence, loss of adhesion, staining, and failure of floor coatings or membranes. Applying a low-permeability coating does not eliminate the source of the moisture.

Roller Application

Roller application uses a rotating cylindrical cover to transfer and distribute coating over a surface. It is common for architectural painting, floors, roofs, tanks, walls, structural steel, and maintenance work.

Roller cover material, nap length, core design, width, coating viscosity, application pressure, loading technique, and substrate texture affect film thickness and appearance.

A roller may not achieve the same film thickness in one pass as airless spray. Wet-film thickness should be checked when a specified protective film build is required.

Roller Nap

Roller nap is the length and density of fibers extending from a roller cover. Shorter nap is generally used for smoother surfaces and finer finishes, while longer nap helps reach into rough or textured surfaces.

An unsuitable nap can create excessive texture, air bubbles, poor coverage, fiber shedding, or inadequate coating placement in surface irregularities. The cover material must also be compatible with the coating and solvent.

Roof Coating

A roof coating is a fluid-applied material used to protect, restore, waterproof, or improve the performance of a roof surface. Common technologies include acrylic, silicone, polyurethane, asphaltic, and other elastomeric systems.

A roof coating is not a substitute for correcting every roofing defect. Wet insulation, active leaks, poor drainage, damaged decking, failed seams, incompatible materials, and structural problems must be addressed.

Successful installation depends on roof evaluation, cleaning, adhesion testing, repairs, primer where required, reinforcement, correct application rate, film thickness, weather conditions, and cure.

Information about reflective roof surfaces is available from the Cool Roof Rating Council.

Roof-Coating Application Rate

Roof-coating application rate is the amount of material applied over a defined roof area. It may be expressed as gallons per 100 square feet, square feet per gallon, litres per square metre, or another specified unit.

Application rate is not always equivalent to final dry-film thickness. Volume solids, surface texture, absorption, material loss, reinforcement, and application technique affect the finished film.

Material quantities should be calculated using the manufacturer’s specified rate and confirmed through wet-film or consumption measurements where required.

Rotary Atomizer

A rotary atomizer uses a rapidly rotating bell or disc to break liquid coating into droplets. It is commonly used in high-production automotive, appliance, and industrial electrostatic finishing.

Coating is delivered to the center of the rotating component and moves outward under centrifugal force. Bell speed, fluid flow, shaping air, voltage, part distance, coating properties, and booth airflow influence atomization and pattern control.

Rotary atomizers can provide high transfer efficiency and finish quality but require careful cleaning, maintenance, grounding, and process control.

Run

A run is a downward movement of liquid coating that forms a narrow, visible trail or heavy ridge before the film sets. A run is closely related to a sag but is often narrower and more pronounced.

Common causes include excessive wet-film thickness, slow gun speed, holding the gun too close, excessive fluid delivery, low viscosity, incorrect reducer, cold substrate, or inadequate flash time between coats.

Repair normally requires allowing the coating to cure sufficiently, leveling or removing the defect, cleaning the area, and recoating according to an approved procedure.

Rust

Rust is the common name for corrosion products formed on iron and steel through reaction with oxygen and moisture. Salts, chemicals, temperature, and wet-dry cycling can accelerate its formation.

Rust may appear as red-brown, orange, dark brown, or black material depending on the corrosion process and environment. Loose or active rust generally must be removed to the preparation grade required by the coating system.

Rust Bloom

Rust bloom is the early appearance of rust on prepared steel. It may occur after cleaning when the surface is exposed to moisture, condensation, high humidity, salts, or contamination.

Rust bloom can develop rapidly on waterjetted, wet-abrasive-blasted, washed, or freshly blast-cleaned steel. The permitted degree of flash rust or rust bloom depends on the preparation standard and coating manufacturer.

Rust-Grade Evaluation

Rust-grade evaluation is the assessment of the amount and distribution of visible rust on a steel surface. Different standards address the initial rust condition of uncoated steel and the degree of rusting through an existing paint film.

For painted steel, ASTM D610 uses a numerical scale based on the percentage of visible rust and identifies distribution patterns such as spot, general, pinpoint, and hybrid rusting.

See ASTM D610, Standard Practice for Evaluating Degree of Rusting on Painted Steel Surfaces.

Rust Creep

Rust creep is the lateral spread of corrosion beneath a coating from a scribe, cut edge, holiday, damaged area, or other break in the protective film.

Rust creep is used to evaluate how effectively a coating system resists corrosion undercutting after the film has been intentionally or accidentally damaged.

A commonly referenced laboratory evaluation method is ASTM D1654, Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments. The exposure method, scribe configuration, cleaning procedure, and rating system must be reported.

Rust Inhibitor

A rust inhibitor is a material or chemical treatment intended to slow the corrosion of iron or steel. It may be part of a primer, cleaning solution, rinse, temporary protective coating, water treatment, or corrosion-control system.

A rust inhibitor does not eliminate the need for appropriate surface preparation or sufficient coating thickness. Its performance depends on concentration, exposure, compatibility, and the complete protective system.

Rust Staining

Rust staining is discoloration caused when iron corrosion products are carried onto or through a coating, concrete surface, wall, roof, or adjacent material.

The stain may originate from exposed fasteners, embedded steel, damaged coating, runoff from another component, or corrosion beneath the film. Cleaning the visible stain without correcting the source may provide only a temporary improvement.

Rust-Preventive Coating

A rust-preventive coating is intended to reduce corrosion of iron or steel. It may provide barrier protection, corrosion inhibition, sacrificial protection, or a combination of mechanisms.

The term does not identify a single chemistry or service life. Product selection must consider surface preparation, environment, exposure duration, film thickness, compatibility, and whether the coating is intended as a temporary or permanent system.

Rust-Through

Rust-through is corrosion that has penetrated the metal substrate and produced an opening or loss of structural section. It is more severe than surface rust or corrosion visible through a coating.

Coating alone cannot restore metal that has lost required thickness or structural integrity. The affected component should be evaluated by qualified personnel before coating repair proceeds.

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Referenced Standards and Industry Resources

• AMPP Standards and Technical Resources
• OSHA Respiratory Protection
• Cool Roof Rating Council
• RAL Colour Standards
• ASTM D610 — Evaluating Degree of Rusting on Painted Steel
• ASTM D1654 — Evaluation After Corrosive Exposure
• ASTM D2794 — Resistance to Rapid Deformation
• ASTM D4417 — Field Measurement of Surface Profile
• ASTM D6386 — Preparation of Hot-Dip Galvanized Surfaces for Painting

Continue Building Your Coatings Vocabulary

Understanding coatings terminology helps applicators, inspectors, equipment operators, specifiers, facility owners, and purchasing professionals communicate more accurately. Continue with the next installment of The Language of Finishing for definitions beginning with the letter S.

For assistance selecting professional spray guns, pumps, pressure equipment, powder coating systems, electrostatic equipment, spray booths, ovens, or genuine replacement parts, contact AirSprayTech.com—The Finishing Authority® at 817.490.1777.

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Tags: paint coatings glossary R, industrial coating terminology, recoat window, coating repair terms, relative humidity painting, respirator safety, roof coating terms, rust evaluation, spray reducer terminology