The Language of Finishing: Paint and Coatings Glossary T

This installment of the AirSprayTech.com Paint and Coatings Industry Glossary covers terms beginning with the letter T. These definitions address coating application, tank linings, thermal-spray coatings, powder coating, inspection testing, film thickness, spray equipment, transfer efficiency, troubleshooting, and two-component materials.

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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T

Taber Abrasion Test

The Taber abrasion test evaluates the resistance of a coating to wear produced by rotating abrasive wheels under controlled conditions.

A coated, flat test specimen rotates beneath weighted abrasive wheels. Coating loss may be evaluated by mass loss, thickness loss, visual change, or another value specified by the test procedure.

Results depend on the abrasive-wheel type, applied load, number of cycles, wheel conditioning, vacuum setting, test panel, coating thickness, cure, and reporting method.

A commonly referenced procedure is ASTM D4060, Standard Test Method for Abrasion Resistance of Organic Coatings by the Taber Abraser.

Tack

Tack is the degree of stickiness remaining on the surface of a coating, adhesive, sealant, or lining. It may be an intended application property or evidence that a coating has not dried or cured sufficiently.

Tack can be affected by coating chemistry, temperature, humidity, ventilation, film thickness, incorrect mixing, solvent entrapment, contamination, or plasticizer migration.

A tacky surface should not automatically be recoated or placed into service. The product data sheet and specified cure-verification method should be consulted.

Tack Coat

A tack coat is a thin layer applied to promote bonding between a substrate or existing layer and a subsequent material.

The term is commonly used in flooring, roofing, paving, waterproofing, adhesives, and some protective coating applications. Depending on the system, the tack coat may need to remain slightly tacky when the next layer is applied.

A tack coat is not identical to every primer, tie coat, or mist coat. The product manufacturer’s terminology and application instructions should control.

Tack-Free Time

Tack-free time is the period required for an applied coating to reach a condition in which its surface no longer exhibits tack under the specified test method.

Tack-free time is not necessarily the same as dry-to-touch time, handle time, recoat time, full cure, or return-to-service time.

Temperature, humidity, air movement, film thickness, coating chemistry, and substrate temperature can change the actual tack-free time.

Tack Rag

A tack rag is a wiping cloth designed to collect fine dust and loose particles immediately before coating. It is commonly used in automotive refinishing, aerospace finishing, cabinet finishing, and other appearance- critical applications.

The tack rag must be compatible with the coating system. Excessive pressure or an unsuitable rag can transfer resin, wax, silicone, or another residue to the surface and cause fisheyes, adhesion problems, or finish defects.

Tank Lining

A tank lining is a protective coating system applied to the interior surface of a tank to protect the substrate, protect the stored material, or perform both functions.

Lining selection must consider the stored product, chemical concentration, temperature, pressure, cleaning method, immersion duration, possible mixtures, and frequency of filling and emptying.

Surface preparation, stripe coating, film thickness, continuity, cure, ventilation, and holiday testing are especially important. A lining should not be placed into service until it has achieved the required cure.

Tape-Adhesion Test

A tape-adhesion test evaluates the adhesion of a coating by making specified cuts in the film, applying pressure-sensitive tape, removing it in a controlled manner, and rating the amount of coating removed.

The test is useful for identifying relatively large differences in adhesion. It does not produce an absolute tensile bond-strength value and should not be interpreted as equivalent to a pull-off adhesion test.

Results can be affected by coating thickness, cure, substrate, cutting tool, spacing, tape, application pressure, dwell time, removal technique, temperature, humidity, and operator skill.

The commonly referenced method is ASTM D3359, Standard Test Methods for Rating Adhesion by Tape Test.

Tape Test Method A

ASTM D3359 Test Method A uses an X-cut made through the coating to the substrate. Pressure-sensitive tape is applied over the cut, removed, and the coating is rated according to the standard.

The current ASTM method primarily intends Method A for coating systems greater than 5 mils, or 125 microns, in total thickness. The complete standard should be consulted for cutting, tape application, removal, and rating requirements.

Tape Test Method B

ASTM D3359 Test Method B uses a lattice or cross-cut pattern made through the coating. Tape is applied over the grid, removed, and the amount of coating detached from the cut area is rated.

The current ASTM method primarily intends Method B for coating systems less than 5 mils, or 125 microns, in total thickness. Cut spacing and test limitations must be selected according to the standard.

Target

In spray finishing, the target is the part, component, structure, or surface intended to receive the coating. The target may also refer to a specific area used for pattern testing, film-thickness verification, or process adjustment.

Target size, shape, orientation, temperature, grounding, movement, and distance from the applicator affect deposition and transfer efficiency.

Target Film Thickness

Target film thickness is the wet- or dry-film thickness an applicator aims to achieve so the completed work complies with the specified range.

The target is not always the same as the minimum permitted thickness. Applicators often aim near the center of the allowable range to accommodate normal application and measurement variation without producing low or excessively high areas.

Technical Data Sheet — TDS

A technical data sheet is a manufacturer’s document describing a product’s intended use, performance, application requirements, surface preparation, mixing, thinning, film thickness, coverage, drying, cure, recoat intervals, and environmental limits.

The TDS may also be called a product data sheet, or PDS. It should not be confused with the Safety Data Sheet, which addresses hazards and safe handling.

Always obtain the current data sheet for the exact product, color, region, and intended application.

Telegraphing

Telegraphing is the visible appearance of an underlying joint, repair, scratch, texture, filler edge, surface defect, or coating transition through the finish coat.

Common causes include inadequate filling or sanding, different absorption rates, insufficient surfacer thickness, shrinkage, movement, gloss differences, or an abrupt repair edge.

Telegraphing is common in automotive, aerospace, wood, wall, floor, roof, and composite-finishing applications.

Temperature

Temperature is a critical coating-application and curing variable. Air, surface, material, oven, and part-metal temperatures may all need to be measured separately.

Temperature affects viscosity, atomization, solvent evaporation, water evaporation, condensation risk, induction time, pot life, recoat interval, cure, outgassing, and final film properties.

An air-temperature reading alone does not establish that a surface or coating material is within its permitted application range.

Temperature Differential

Temperature differential is the difference between two measured temperatures. In field coating, one important differential is the difference between surface temperature and dew-point temperature.

Specifications commonly require the surface to remain a stated number of degrees above the dew point to reduce the risk of condensation. The actual requirement must be obtained from the project specification and product data sheet.

Temperature Recorder

A temperature recorder is an instrument that measures and stores temperature readings over time. It may monitor ambient conditions, coating storage, oven performance, part-metal temperature, or curing conditions.

The instrument’s range, accuracy, probe type, response time, calibration status, and placement must be suitable for the intended measurement.

Tensile Adhesion

Tensile adhesion describes resistance to a force applied perpendicular to the coating surface. It is commonly evaluated using portable pull-off adhesion equipment.

The result represents the weakest plane encountered within the complete test assembly. Separation may occur at the substrate, between coating layers, within a coating layer, within the adhesive, or at the loading fixture.

A pull-off strength value should always be reported with the failure location and test procedure. ASTM D4541 is commonly used for metal substrates, while ASTM D7234 addresses coatings on concrete.

Test Area

A test area is a defined portion of a coated surface selected for one or more measurements or examinations. It may be established by square footage, component, production lot, elevation, tank section, or another logical division.

The specification should define how areas are selected, how many tests are required, and how the results are used for acceptance.

Test Method

A test method is a documented procedure describing how a material, coating, surface, or property is to be evaluated.

The standard designation alone may not provide complete direction. Many standards contain multiple procedures, instrument types, options, or test conditions that must be selected by the specification.

Test reports should identify the standard number, edition, method or procedure, equipment, conditions, results, and any permitted deviations.

Test Panel

A test panel is a prepared specimen used to apply, cure, compare, or test a coating under controlled conditions. It may be used for color approval, process qualification, adhesion, hardness, corrosion, impact, flexibility, weathering, or other evaluation.

The panel substrate, preparation, profile, coating thickness, application method, and cure must be representative of the intended comparison.

Test Patch

A test patch is a small area of actual or representative substrate prepared and coated before full-scale work begins. It may be used to examine adhesion, compatibility, appearance, coverage, surface preparation, or application technique.

The patch should remain in place for an appropriate period and be evaluated using agreed criteria. A successful test patch reduces uncertainty but cannot guarantee performance across an entire structure with variable conditions.

Texture

Texture is the visible or tactile surface pattern of a coating. It may be intentionally produced or may result from substrate roughness, application conditions, atomization, flow, powder formulation, or a coating defect.

Intentional textures include orange peel, wrinkle, hammertone, sand texture, and nonskid finishes. Acceptance should be based on an approved sample or measurable requirement.

Theoretical Coverage

Theoretical coverage is the calculated area a coating can cover at a specified dry-film thickness if there is no material loss and the surface is perfectly smooth.

It is calculated from the coating’s volume solids and required dry-film thickness. Actual coverage is lower because of overspray, surface profile, application waste, container residue, hose loss, part geometry, and environmental conditions.

Theoretical Wet-Film Thickness

Theoretical wet-film thickness is the wet thickness calculated to produce a required dry-film thickness based on the coating’s stated volume solids.

WFT = DFT ÷ Volume Solids as a Decimal

If a coating is 70 percent solids by volume and the required dry-film thickness is 7 mils, the theoretical wet-film thickness is 10 mils before accounting for permitted thinning or surface effects.

Thermal Conductivity

Thermal conductivity describes a material’s ability to conduct heat. It is relevant to thermal-insulating coatings, fire-protective systems, heated process equipment, and oven curing.

A coating’s thermal performance depends on more than conductivity alone. Film thickness, substrate, temperature range, moisture, surface condition, emissivity, and the complete system must also be considered.

Thermal Cycling

Thermal cycling is repeated exposure to changing temperatures. Heating and cooling cause substrates and coatings to expand and contract.

If coating layers and substrates move at different rates, stress can develop and contribute to cracking, delamination, checking, loss of adhesion, or failure around joints and fasteners.

Thermal cycling is important in aerospace, automotive, rail, pipelines, roofs, tanks, exhaust equipment, industrial ovens, and exterior structures.

Thermal Expansion

Thermal expansion is the dimensional change that occurs when a material’s temperature changes. Different substrates and coating materials have different coefficients of thermal expansion.

Coating flexibility, adhesion, thickness, joint design, and service-temperature range must accommodate expected movement. Rigid coatings may crack when applied across moving joints or dissimilar materials.

Thermal Spray Coating

Thermal spraying is a process in which metallic, ceramic, polymeric, or composite feedstock is heated and projected onto a prepared surface to form a coating.

Common processes include flame spray, electric arc spray, plasma spray, and high-velocity oxygen fuel spraying. Thermal-sprayed zinc and aluminum are used for corrosion protection of steel.

Surface preparation, profile, spray parameters, coating thickness, porosity, adhesion, and sealing can strongly affect performance. Thermal spray requirements are available through AMPP and other applicable standards organizations.

Thermoplastic Coating

A thermoplastic coating softens and flows when heated and hardens again when cooled. It does not rely on the same permanent crosslinking reaction used by thermosetting coatings.

Thermoplastic powder coatings include some nylon, polyethylene, polyvinyl chloride, and fluoropolymer systems. They may be applied by electrostatic spray, fluidized bed, or dipping a preheated part into powder.

Thermoset Powder Coating

A thermoset powder coating melts, flows, and chemically crosslinks when heated through its specified cure schedule.

Common thermoset powder families include epoxy, polyester, epoxy-polyester hybrid, polyurethane, and acrylic technologies.

After proper cure, thermoset powder does not simply remelt into its original form when reheated. Underbaking can leave the coating incompletely cured, while excessive heat exposure may cause discoloration or degradation.

Thinner

A thinner is a liquid added to a coating to reduce viscosity, modify application properties, or clean compatible equipment. The terms thinner and reducer are often used interchangeably, although manufacturers may distinguish between them.

Only the thinner identified by the coating manufacturer should be used. A general-purpose solvent may have the wrong solvency or evaporation rate and cause lifting, poor flow, dry spray, slow cure, solvent pop, or loss of performance.

Thinning

Thinning is the controlled addition of an approved thinner, reducer, water, or other permitted liquid to a coating.

Thinning affects viscosity, wet-film thickness, applied volume solids, sag resistance, drying, atomization, coverage, emissions, and final film build. The amount added should be measured and recorded.

Environmental regulations or project specifications may prohibit thinning even when a product data sheet permits a limited amount.

Thixotropy

Thixotropy is a time-dependent flow property in which a material becomes less viscous when subjected to mixing, pumping, or application force and gradually rebuilds viscosity when left at rest.

Thixotropic coatings can be easier to spray or brush while still resisting sagging after application. Excessive mixing, temperature changes, unauthorized thinning, and incorrect pump selection can alter their behavior.

Three-Coat System

A three-coat system commonly consists of a primer, intermediate coat, and finish coat. Each layer performs a different function within the complete protective system.

The primer may provide adhesion or corrosion protection. The intermediate coat builds barrier thickness, and the finish coat provides color, weathering resistance, chemical resistance, gloss, or cleanability.

Stripe coats may be required in addition to the three full coats and should not automatically be counted as one of them.

Throwing Power

Throwing power is the ability of an electrically deposited coating to reach and build film in recessed, shielded, or difficult-to-access areas.

The term is commonly used in electrocoating and may also be discussed in electrostatic liquid or powder application. Part geometry, electrical field strength, conductivity, bath or coating properties, voltage, current, and application time affect throwing power.

Tie Coat

A tie coat is an intermediate layer applied to improve adhesion or compatibility between otherwise difficult coating layers.

It may be used over inorganic zinc, aged coatings, antifouling systems, elastomeric materials, unknown existing finishes, or other surfaces requiring a transition layer.

A tie coat must be approved for both the underlying surface and the subsequent coating. It cannot correct loose, contaminated, or poorly adhered existing material.

Time at Temperature

Time at temperature is the period during which a coated part remains at or above the temperature required for cure. It is different from total oven dwell time.

A heavy part may spend much of its oven dwell time heating to the specified metal temperature. The required cure period begins only after the coating or part reaches the temperature defined by the manufacturer.

Tinting

Tinting is the controlled addition of colorant to adjust or produce a coating color. It may occur at the manufacturer, distributor, paint store, mixing room, or production facility.

Colorant type and amount can affect opacity, drying, viscosity, gloss, weathering, and application properties. Only tint systems approved for the coating should be used.

Tip Extension

A tip extension moves an airless or air-assisted airless spray tip farther from the spray gun body. It can help reach ceilings, floors, walls, structural members, tanks, and other difficult areas.

The extension must be pressure-rated and compatible with the gun and tip guard. Longer extensions can increase operator fatigue and make it more difficult to maintain correct gun angle and distance.

A tip extension is not a substitute for approved access equipment or fall protection.

Tip Guard

A tip guard surrounds an airless spray tip and helps reduce accidental contact with the tip while providing the alignment and retention required by the spray system.

A tip guard does not eliminate the danger of high-pressure injection. Hands and body parts must always be kept away from the spray stream, and the pressure-relief procedure must be followed before servicing equipment.

Tip Orifice

The tip orifice is the opening through which pressurized coating passes in airless and air-assisted airless spraying. It is a major factor controlling material flow.

Larger orifices generally deliver more coating at the same pressure. Actual output also depends on material viscosity, pressure, tip wear, filters, hose restrictions, and pump capacity.

Tip Wear

Tip wear is the gradual enlargement and erosion of a spray-tip orifice caused by coating flow and abrasive material.

A worn airless tip typically delivers more material while producing a narrower, less-defined fan. This increases coating consumption and can create runs, uneven film thickness, and excessive pump demand.

Pressure should not be increased to compensate for a worn tip. The tip should be inspected and replaced when its performance is no longer acceptable.

Topcoat

A topcoat is the final coating layer in a multi-coat system. It commonly provides color, gloss, weathering resistance, chemical resistance, abrasion resistance, cleanability, or another finished property.

The topcoat must be compatible with the primer and intermediate coat and applied within the permitted recoat window. A decorative topcoat cannot compensate for inadequate surface preparation or insufficient protective film beneath it.

Touch-Up

Touch-up is localized coating work used to repair small areas damaged by handling, assembly, welding, cutting, fastening, inspection, transportation, or installation.

The repair area should be cleaned and prepared to the required standard. The touch-up coating must be compatible with the substrate, surrounding coating, appearance requirements, and service environment.

A convenient aerosol or brush-on product should not be substituted for the specified repair coating without approval.

Transfer Efficiency

Transfer efficiency is the percentage of sprayed coating material that deposits on the intended target.

Transfer Efficiency = Material Deposited on the Target ÷ Material Sprayed × 100

Transfer efficiency is influenced by spray technology, atomization, pressure, gun distance, gun angle, part geometry, grounding, booth airflow, coating properties, operator technique, and production arrangement.

High transfer efficiency can reduce material consumption, overspray, filter loading, emissions, and cleanup. It should not be confused with material utilization or powder-recovery efficiency.

Transition Area

A transition area is the region where one substrate, coating system, repair, thickness, geometry, or service condition changes to another.

Transitions around joints, repairs, penetrations, dissimilar materials, floor-to-wall connections, and coating terminations often require feathering, reinforcement, sealant, stripe coating, or another special detail.

Trigger

The trigger is the spray-gun control operated by the applicator to start and stop air, fluid, or both. Trigger design depends on the spray technology.

On many air spray guns, an initial trigger movement begins airflow and further movement opens the fluid needle. On airless guns, the trigger releases pressurized fluid through the tip.

The trigger safety should be engaged whenever the airless gun is not in use. The safety does not replace the required pressure-relief procedure.

Triggering Technique

Triggering technique is the coordinated starting and stopping of coating flow during a spray pass. The gun generally begins moving before full coating flow starts and continues moving as the trigger is released.

Correct triggering reduces heavy film at pass ends, material waste beyond the target, and excessive buildup on edges.

Troubleshooting

Troubleshooting is the systematic process of identifying and correcting the cause of an application, equipment, process, or coating problem.

Effective troubleshooting begins by defining the defect, determining when and where it occurs, reviewing recent changes, and separating possible equipment, material, environmental, substrate, and operator causes.

Changing several variables at once can hide the true cause. When safe and practical, adjust one controlled variable at a time and document the result.

Turbine HVLP

A turbine HVLP system uses a high-volume blower or turbine to supply warm, low-pressure atomizing air to the spray gun. It does not require a conventional compressed-air supply for atomization.

Turbine systems are used for wood finishing, cabinets, furniture, automotive spot work, mobile refinishing, and other applications.

The number of turbine stages, hose length, air temperature, gun design, fluid nozzle, coating viscosity, and material flow affect performance. Warm turbine air can change viscosity and evaporation behavior during extended operation.

Two-Coat System

A two-coat system contains two complete coating layers. Common examples include primer and topcoat or basecoat and clear coat.

Each coat must achieve its required thickness and function. Two coats applied with insufficient combined thickness do not provide the same protection as a properly applied two-coat system.

Stripe coats, mist coats, and localized touch-up layers may be required in addition to the two full coats.

Two-Component Coating — 2K

A two-component coating is supplied as two separate parts that must be mixed before application. It is commonly called a 2K coating.

The components may be identified as base and activator, resin and hardener, Part A and Part B, or other manufacturer-specific names. Combining them starts a chemical reaction that produces the cured film.

Accurate proportioning, thorough mixing, induction time where required, material temperature, pot life, and application conditions are essential. An incorrect ratio can cause incomplete cure, brittleness, softness, poor adhesion, reduced chemical resistance, or premature failure.

Two-Stage Coating System

A two-stage coating system uses two distinct finish stages, commonly a color basecoat followed by a protective clear coat.

Two-stage systems are common in automotive, aerospace, transportation, and appearance-critical OEM finishing. The basecoat provides color and effect, while the clear coat contributes gloss, depth, ultraviolet resistance, and environmental protection.

Flash time, basecoat coverage, metallic orientation, contamination control, clear-coat thickness, and cure all affect the final appearance.

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Referenced Standards and Industry Resources

• AMPP Standards and Technical Resources
• Powder Coating Institute
• OSHA Respiratory Protection
• ASTM D1640 — Drying, Curing, and Film-Formation Times
• ASTM D2794 — Resistance to Rapid Deformation
• ASTM D3359 — Rating Adhesion by Tape Test
• ASTM D4060 — Abrasion Resistance by the Taber Abraser
• ASTM D4541 — Pull-Off Strength of Coatings
• ASTM D7234 — Pull-Off Adhesion Strength on Concrete

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 letters U and V.

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.

Copyright © 2026 Azimuth Spray Systems, LLC. All rights reserved. AirSprayTech.com—The Finishing Authority®. No portion of this glossary may be reproduced, distributed, or republished without prior written permission.

Tags: paint coatings glossary T, tape adhesion test, thermal spray coatings, tank lining terms, transfer efficiency, spray tip terminology, thermoset powder coating, two-component coatings, coating troubleshooting