Glossary

100% solids

A coating containing essentially no volatile solvent, so the dry film thickness nearly equals the wet film thickness. Many plural-component polyureas and some epoxies are formulated this way.

Abrasion resistance

A coating's ability to resist wear from rubbing, scraping or traffic. It is often measured with a rotary abrader as weight loss after a set number of cycles, per ASTM D4060.

Abrasive

Hard particulate media, such as steel grit, steel shot, garnet, aluminum oxide or mineral slag, propelled to clean and profile surfaces. Particle size, shape and hardness determine profile depth and pattern.

Abrasive blasting

Propelling abrasive at high velocity with compressed air, centrifugal wheels or water to remove rust, mill scale and old coatings and create a surface profile.

Acid etching

Treating concrete with dilute acid to remove laitance and open the surface. It produces only a light profile, leaves residues and is generally not recommended for high-performance coatings.

Acrylic

A resin family based on acrylic and methacrylic polymers, used in waterborne and solvent-borne coatings. Acrylics offer good UV and color stability and are widely used in architectural and light-industrial finishes.

Adhesion

The bond between a coating and its substrate or a previous coat, arising from mechanical interlocking and chemical attraction. It depends heavily on surface cleanliness and profile.

Adhesive failure

Separation at the interface between coating and substrate or between two coats, rather than within a layer. It usually points to contamination, inadequate profile or incompatibility.

Airless spray

Application in which a pump forces coating at high pressure through a small tip orifice, atomizing it without compressed air. It is fast and suits high-build coatings over large areas.

Aliphatic

Describes isocyanates or resins built from non-aromatic (straight-chain or ring-shaped but non-benzenoid) structures. Aliphatic polyurethanes and polyureas resist UV yellowing and chalking, so they are preferred for color- and gloss-retentive topcoats.

Alkyd

A polyester resin modified with drying oils or fatty acids that cures by reaction with atmospheric oxygen. Alkyds are easy to apply and tolerant of marginal surfaces but have limited chemical and alkali resistance.

Alligatoring

Wide, deep cracking in a pattern resembling alligator skin, typically from a hard coat over a softer one or from aging of oil-based films.

Amine blush

A waxy or greasy film of amine carbamates formed when amine curing agents react with moisture and carbon dioxide during cure. It can cause intercoat adhesion failure and must be washed off before recoating.

Amine curing agent

A hardener containing reactive amine hydrogens that crosslinks epoxy resins. Types include aliphatic and cycloaliphatic amines, polyamides, amidoamines and phenalkamines, each affecting cure speed, blush tendency and flexibility.

Anchor profile

The peak-to-valley roughness created on a substrate by blasting or mechanical preparation, which increases surface area for mechanical adhesion. Also called surface profile or anchor pattern.

Anode

The electrode in a corrosion cell where oxidation occurs and metal dissolves, releasing electrons. On a corroding structure, anodic areas are where metal loss is concentrated.

Antifouling coating

A marine coating that deters attachment of organisms such as barnacles and algae, typically by releasing biocides. Use of certain biocides is restricted by international and national rules.

Aromatic

Describes resins or isocyanates containing benzene-ring structures, such as MDI or TDI. Aromatic systems are typically tough and economical but darken and chalk under UV exposure, so they are often topcoated outdoors.

ASTM D4417

Standard test methods for field measurement of blasted steel surface profile: visual comparator (Method A), depth micrometer (Method B) and replica tape (Method C).

Back-rolling

Rolling a freshly sprayed coat to work it into surface pores and irregularities and even out film thickness, common on concrete and rough surfaces.

Barrier protection

Corrosion control by a film that restricts water, oxygen and ions from reaching the substrate. Effectiveness depends on thickness, low permeability, adhesion and freedom from defects.

Binder

The film-forming component, usually a resin, that holds pigments together and bonds to the substrate. It largely determines a coating's chemical resistance, flexibility and durability.

Bio-based resin

A resin partly or wholly derived from renewable feedstocks such as plant oils, sugars or cashew nutshell liquid. Bio-based content alone does not determine overall environmental impact or performance.

Bisphenol A epoxy

The most widely used epoxy resin, made from bisphenol A and epichlorohydrin. It offers strong adhesion and chemical resistance but chalks under sunlight.

Blistering

Dome-shaped bubbles in a coating caused by loss of adhesion and accumulation of liquid or gas beneath or within the film. Causes include osmosis, solvent entrapment and cathodic reactions.

Bresle method

A surface-sampling method in which water is injected into an adhesive patch cell, then its conductivity is measured to estimate soluble salt density; described in ISO 8502-6 and ISO 8502-9.

Broadcast

Scattering aggregate such as quartz sand, aluminum oxide or decorative flakes into a wet coating for slip resistance, texture or appearance, then removing excess and sealing.

Brush-off blast

SSPC-SP 7/NACE No. 4: blast cleaning that removes loose mill scale, rust and coating while allowing tightly adherent material to remain. Roughly comparable to ISO 8501-1 Sa 1.

Cathode

The electrode in a corrosion cell where reduction occurs, such as oxygen reduction or hydrogen evolution, consuming electrons. The cathode itself does not corrode.

Cathodic disbondment

Loss of adhesion between a coating and steel under cathodic protection, driven by alkaline conditions and hydrogen generated at exposed steel at coating defects. Coatings for buried and submerged service are tested for resistance to it.

Cathodic protection (CP)

A technique that makes a metal structure the cathode of an electrochemical cell to stop corrosion, using sacrificial anodes or impressed current. It is commonly combined with coatings on pipelines, tanks and marine structures.

Chalking

A powdery surface layer formed as UV light breaks down the binder and releases pigment. It is typical of epoxies and aromatic urethanes exposed outdoors.

Checking

Fine, shallow cracks that do not penetrate to the substrate, usually caused by film shrinkage and aging.

Coal tar epoxy

An epoxy modified with coal tar pitch, historically used for immersion and buried steel. Its use has declined because of health and environmental concerns over polycyclic aromatic hydrocarbons.

Coalescence

The process by which latex polymer particles in a waterborne coating fuse into a continuous film as water evaporates. It requires temperatures above the minimum film-formation temperature.

Coating inspector

A qualified person who verifies that surface preparation, environmental conditions, application and the finished film meet the specification, documenting results at defined hold points.

Coating system

The complete combination of surface preparation and successive coats, such as primer, intermediate and topcoat, specified to work together for a given exposure.

Cohesion

The internal strength holding a coating layer together. A pull-off test that breaks within a single layer indicates cohesive failure rather than loss of adhesion.

Commercial blast

SSPC-SP 6/NACE No. 3: blast cleaning in which random staining is limited to no more than 33% of each unit area. Roughly comparable to ISO 8501-1 Sa 2.

Concrete surface profile (CSP)

A ten-step scale of concrete roughness from CSP 1 (nearly flat) to CSP 10 (very rough), defined in ICRI 310.2R with replica chips for visual and tactile comparison.

Conventional air spray

Spraying in which compressed air at the gun cap atomizes the coating. It gives a fine finish but has relatively low transfer efficiency and significant overspray.

Cool roof coating

A reflective roof coating, usually light colored, with high solar reflectance and thermal emittance that reduces roof surface temperature and cooling load.

Corrosion

The deterioration of a material, usually a metal, through chemical or electrochemical reaction with its environment. Steel corrosion requires an anode, cathode, electrolyte and metallic path.

Corrosivity category

An ISO 12944 classification of atmospheric environments from C1 (very low) to C5 (very high) and CX (extreme), plus Im1–Im4 for immersion and buried exposure.

Cratering

Small bowl-shaped depressions in a coating caused by contamination, such as oil, silicone or dust, that locally lowers surface tension during flow-out.

Crevice corrosion

Localized corrosion in shielded gaps, such as under gaskets, lap joints or deposits, where differences in oxygen or ion concentration create an aggressive micro-environment.

Cross-cut test

An adhesion test in which a lattice pattern is cut through the coating, tape is applied and removed, and detachment is rated from 0B to 5B; ASTM D3359 Method B, generally for films up to 5 mils (125 µm).

Crosslink density

The number of chemical crosslinks per unit volume in a cured polymer network. Higher density usually increases hardness, chemical resistance and Tg but reduces flexibility and impact resistance.

Crosslinking

The formation of covalent bonds between polymer chains that converts liquid resin into a three-dimensional network. It underlies the cure of thermosets such as epoxies and polyurethanes.

Cure

The chemical process, such as crosslinking or oxidation, by which a coating develops its final properties. It is distinct from drying, which is simply the loss of solvent or water.

Cyclic corrosion test

A laboratory test that cycles specimens through salt fog, drying and humidity phases. It typically correlates better with real outdoor exposure than continuous salt spray.

Cycloaliphatic amine

An epoxy curing agent based on ring-structured, non-aromatic amines. It offers good chemical resistance, gloss and lower blush tendency than many straight-chain aliphatic amines.

Delamination

Separation of a coating from the substrate or between coats, often in sheets. Common causes are poor surface preparation, contamination and missed recoat windows.

Dew point

The temperature at which air becomes saturated and water vapor condenses on a surface. Coating onto a surface at or near dew point risks invisible condensation and adhesion failure.

Dew point spread

The margin between surface temperature and dew point. Specifications and data sheets commonly require the surface to be at least 5 °F (3 °C) above the dew point during application and cure.

Diamond grinding

Using rotating diamond-segment heads to remove laitance, sealers and high spots from concrete, typically producing a light profile in the CSP 1–3 range.

Dolly

A metal stud or loading fixture glued to a coating surface for pull-off adhesion testing. The force needed to detach it is recorded with the location of the break.

Dry film thickness (DFT)

The thickness of a coating after it has dried or cured, usually expressed in mils or micrometers. It is the primary thickness requirement in most specifications.

Dry spray

Spray-applied coating that partially dries before reaching the surface, leaving a rough, sandy, porous film with poor adhesion. Causes include excessive gun distance, wind, heat and overly fast solvents.

Duplex system

A paint system applied over hot-dip galvanizing or thermal-sprayed metal. The two layers protect synergistically, typically lasting longer than either alone.

Edge rounding

Grinding sharp steel edges to a radius so coatings do not pull thin there during cure. Many specifications require a minimum radius for immersion or severe service.

Efflorescence

White crystalline salt deposits left on concrete or masonry when migrating water evaporates. It signals moisture movement and must be removed, and its cause addressed, before coating.

Electrolyte

An ionically conductive medium, such as water containing dissolved salts, that allows current to flow between anode and cathode in a corrosion cell.

Electronic coating thickness gauge

A handheld instrument that measures DFT nondestructively, using magnetic induction on ferrous substrates and eddy current on non-ferrous metals. Classified as a Type 2 gauge under SSPC-PA 2.

Electrostatic spray

Application in which coating particles receive an electrical charge and are attracted to a grounded part, improving transfer efficiency and wrapping around edges.

Epoxy

A thermoset resin containing reactive epoxide groups, cured with amines or other hardeners. Epoxies provide strong adhesion and chemical resistance but chalk under UV exposure.

Exempt solvent

A volatile compound that regulators have excluded from the VOC definition because of its negligible contribution to ground-level ozone formation, such as acetone in many jurisdictions. Exemptions vary by jurisdiction.

Exotherm

Heat released by a curing reaction. Large mixed masses can overheat, sharply shortening pot life and, in extreme cases, causing smoking or charring.

Fading

Loss of color strength from UV degradation of pigments or binder. Organic pigments and aromatic binders are particularly susceptible.

FEVE

Fluoroethylene vinyl ether, a fluoropolymer resin that can be crosslinked with isocyanates at ambient temperature. It provides long-term gloss and color retention in field- and shop-applied topcoats.

Filiform corrosion

Thread-like corrosion tracks that spread beneath a thin coating, commonly on aluminum and steel in humid conditions, starting from defects or edges.

Fisheyes

Round separations where wet coating pulls away from small spots of contamination such as oil or silicone, exposing the surface beneath in an eye-like pattern.

Flash rust

A light rust film that forms rapidly on freshly cleaned steel, especially after waterjetting or wet abrasive blasting. Acceptable levels (commonly light, moderate or heavy) depend on the specification and coating.

Flash-off time

The interval for solvents to evaporate from a wet film before the next coat or force curing. Insufficient flash-off can trap solvent and cause pinholes or blistering.

Foul-release coating

A low-surface-energy marine coating, often silicone or fluoropolymer based, that minimizes organism adhesion so fouling releases under water flow rather than by biocide action.

Full cure

The point at which a coating reaches its final designed properties, such as hardness and chemical resistance. It can take days or weeks and depends strongly on temperature.

Fusion-bonded epoxy (FBE)

A thermosetting epoxy powder applied to preheated steel, where it melts, flows and cures into a tough film. It is widely used on pipeline exteriors and reinforcing bar.

Galvanic corrosion

Accelerated corrosion of the more active metal when two dissimilar metals are electrically connected in an electrolyte. A small anode coupled to a large cathode is especially damaging.

Galvanic series

A ranking of metals and alloys by their corrosion potential in a specific electrolyte, usually seawater. When two are coupled, the more active (anodic) one tends to corrode.

Gel time

The time after mixing at which a reacting resin turns from a liquid into a soft gel and no longer flows. It characterizes fast-reacting systems such as polyurea.

Glass transition temperature (Tg)

The temperature range over which an amorphous polymer changes from a hard, glassy state to a softer, rubbery state. Service near or above Tg typically reduces hardness and chemical resistance.

Hand tool cleaning

SSPC-SP 2: removal of loose rust, mill scale and paint using hand tools such as wire brushes, scrapers and sandpaper. Tightly adherent material may remain.

Hazardous air pollutants (HAPs)

Substances designated by US federal law as toxic air pollutants, including some coating solvents such as toluene and xylene. HAP emissions are regulated separately from VOCs.

High-solids coating

A solvent-borne coating formulated with less solvent and higher volume solids, reducing VOC emissions and building more film per coat.

High-voltage spark testing

Holiday detection in which an electrode at a voltage set for the coating's thickness passes over the film; a spark to the substrate marks a discontinuity. Used on thicker films per ASTM D5162 and NACE SP0188.

Holiday

A discontinuity in a coating, such as a pinhole, void, skip or thin spot, that exposes the substrate. Holidays are critical defects in immersion and buried service.

Hot-dip galvanizing

Immersing fabricated steel in molten zinc to form metallurgically bonded zinc–iron alloy layers and an outer zinc layer, which protect by both barrier and galvanic action.

HVLP

High-volume, low-pressure spraying that atomizes coating with a large volume of air at low cap pressure. It reduces overspray and improves transfer efficiency compared with conventional air spray.

Hydrogen sulfide attack

Degradation in sewers where bacteria convert hydrogen sulfide gas into sulfuric acid on exposed concrete and metal surfaces, a major reason for lining wastewater structures.

Immersion service

Exposure in which a coating is continuously or frequently submerged in water, chemicals or soil. It demands low permeability, excellent adhesion, clean surfaces and holiday-free films.

Impingement mixing

Mixing in which two components collide at high pressure inside the spray gun's mix chamber. It is used for fast-reacting systems such as polyurea and spray foam.

Induction time

A waiting period after mixing some two-component coatings, mainly epoxies, before application. It lets the reaction begin, improving cure and reducing blush; not all products require it. Also called sweat-in time.

Industrial blast

SSPC-SP 14/NACE No. 8: blast cleaning that allows traces of tightly adherent mill scale, rust and coating on no more than 10% of each unit area.

Inorganic zinc (IOZ)

A zinc-rich primer with a silicate binder, commonly ethyl silicate. It offers excellent corrosion and heat resistance but needs very clean blasted steel and humidity to cure, and can mud-crack if applied too thick.

Intercoat adhesion

The bond between successive coats in a system. It depends on compatibility, cleanliness between coats and applying the next coat within the recoat window.

Intercoat delamination

Separation between two coats of a system, often caused by exceeding the recoat window, amine blush, contamination or incompatible products.

ISO 12944

An international standard series on corrosion protection of steel structures by protective paint systems, covering environments, design, surface preparation, systems, durability and testing.

ISO 8501-1

International standard giving photographic grades of steel cleanliness: Sa 1, Sa 2, Sa 2½ and Sa 3 for blast cleaning and St 2 and St 3 for hand and power tool cleaning, plus initial rust grades A–D.

Isocyanate

A reactive compound containing –N=C=O groups that forms polyurethanes with polyols and polyureas with amines. Isocyanates are respiratory and skin sensitizers, so ventilation and respiratory protection are essential.

Laitance

A weak, powdery layer of cement fines and water that rises to the surface of fresh concrete. It must be removed before coating because its low strength leads to delamination.

Lead-based paint

Paint containing lead compounds, common on older steel structures and buildings. Disturbing it generates hazardous dust and waste and is subject to worker-protection and environmental regulations.

Life-cycle assessment (LCA)

A standardized method for quantifying the environmental impacts of a product across its life, from raw materials through manufacture, use and disposal.

Lining

A coating applied to the interior of a tank, pipe or vessel in contact with stored contents. Linings are generally thicker and inspected more rigorously than atmospheric coatings.

Loss factor

An allowance for material lost to overspray, surface roughness, container residue and waste when estimating practical coverage. It varies widely with application method and part geometry.

Low-voltage holiday detector

A wet-sponge detector, typically operating below 100 volts, that signals when moistened sponge contact reaches conductive substrate through a pinhole. Used on thinner films.

Magnetic pull-off gauge

A mechanical DFT gauge in which a permanent magnet is pulled from a coated ferrous surface; the force needed indicates coating thickness. Classified as Type 1 under SSPC-PA 2.

Microbiologically influenced corrosion (MIC)

Corrosion initiated or accelerated by microorganisms, such as sulfate-reducing or acid-producing bacteria, often under biofilms or deposits in water, wastewater and oil and gas systems.

Mill scale

A layer of iron oxides formed on hot-rolled steel during manufacture. It is cathodic to steel and tends to crack and lift, so it is usually removed before high-performance coating.

Mist coat

A very thin, often thinned coat applied over porous surfaces such as inorganic zinc to displace trapped air before the full coat, reducing pinholes and bubbling.

Mix ratio

The specified proportion, by volume or weight, in which coating components must be combined. Off-ratio material may remain soft or tacky, or become brittle.

Moisture vapor emission rate (MVER)

The rate at which water vapor leaves a concrete slab, measured with the calcium chloride test (ASTM F1869) and reported in lb per 1,000 ft² per 24 hours.

Moisture-cure urethane

A single-component polyurethane whose isocyanate groups react with atmospheric humidity to cure. It tolerates cool, humid conditions but can form carbon dioxide bubbles if applied too thick.

Mud cracking

A network of deep, irregular cracks resembling dried mud, typically from applying a highly pigmented or fast-drying coating, such as inorganic zinc, too thick.

Near-white metal blast

SSPC-SP 10/NACE No. 2: blast cleaning that removes all visible oil, grease, dirt, mill scale, rust and coating, with staining limited to no more than 5% of each unit area. Roughly comparable to ISO Sa 2½.

Novolac epoxy

An epoxy resin built on a phenol-formaldehyde (novolac) backbone with more than two epoxide groups per molecule. Its high functionality yields dense crosslinking and superior resistance to acids, solvents and elevated temperatures.

Orange peel

A dimpled surface texture resembling orange skin, caused by poor flow-out from inadequate atomization, high viscosity, improper gun distance or fast-evaporating solvents.

Osmotic blistering

Blistering caused when water diffuses through a coating toward soluble contaminants, such as salts or retained solvents, beneath or within it, building osmotic pressure that lifts the film. Common in immersion service.

Outgassing

Release of air or gas from a porous substrate such as concrete, especially as it warms, which forms bubbles and pinholes in the curing coating.

Overspray

Atomized coating that misses the intended surface and lands elsewhere or dries in the air. It wastes material and can damage nearby surfaces, vehicles or property.

Oxidative cure

Curing in which drying oils or alkyd resins react with atmospheric oxygen to crosslink. It is relatively slow and continues long after the film feels dry.

Passivation

The formation of a thin, protective oxide film that greatly slows corrosion of a metal, as on stainless steel or aluminum. Chlorides and low oxygen can break down this passive layer.

Pencil hardness

A scratch-hardness test in which pencil leads of increasing hardness are pushed across a coating; the hardest lead that does not gouge or scratch it gives the rating.

Permeability

The rate at which water vapor, gases or liquids pass through a coating film. Low permeability improves barrier protection, while breathable coatings let substrate moisture escape.

Phenalkamine

An epoxy curing agent derived from cardanol in cashew nutshell liquid. Phenalkamines enable cure at low temperatures and on damp surfaces and contain partly bio-based content.

Pigment

Fine insoluble particles dispersed in a coating to provide color, opacity, corrosion inhibition or reinforcement.

Pinholes

Tiny holes through a coating film caused by escaping air, gas or solvent, or by surface contamination. They can allow moisture to reach the substrate.

Pinpoint rusting

Small rust spots appearing through a coating, typically where profile peaks protrude through an overly thin film or at pinholes.

Pitting corrosion

Highly localized corrosion forming small cavities that can penetrate deeply while surrounding metal remains largely intact. It is common on passive metals exposed to chlorides.

Plural-component spray

Equipment that meters, heats and mixes two or more reactive components at or near the gun, enabling application of fast-curing coatings with very short pot lives.

Polyamide curing agent

An epoxy curing agent made from dimerized fatty acids and polyamines. Polyamide-cured epoxies offer good flexibility, wetting and water tolerance but somewhat lower chemical resistance than amine-cured systems.

Polyaspartic

An aliphatic polyurea made by reacting polyaspartic ester amines with aliphatic isocyanates. The slower reaction allows roller or squeegee application while still curing quickly with good UV stability.

Polyol

A resin with multiple hydroxyl (–OH) groups that reacts with isocyanate to form polyurethane. Polyester, polyether, acrylic and polycarbonate polyols each influence flexibility, weathering and chemical resistance.

Polysiloxane

A coating whose binder contains a silicon–oxygen backbone, often hybridized with epoxy or acrylic. Polysiloxane topcoats provide excellent UV, gloss and color retention.

Polyurea

An elastomeric polymer formed by reacting an isocyanate with amine-terminated resins. It cures in seconds to minutes and is usually applied with heated plural-component spray equipment.

Polyurethane

A polymer formed by reacting isocyanates with polyols. Coatings range from hard, glossy topcoats to flexible elastomers, and aliphatic grades offer excellent UV resistance.

Pot life

The time after mixing during which a multi-component coating remains usable. It shortens at higher temperatures and with larger mixed volumes because the curing reaction generates heat.

Powder coating

A dry, solvent-free finish of resin and pigment particles, usually applied electrostatically and fused by heat into a continuous film. Common chemistries include epoxy, polyester, epoxy-polyester hybrid and polyurethane.

Power tool cleaning

SSPC-SP 3: removal of loose rust, mill scale and paint using power tools such as grinders and needle guns. Tightly adherent material may remain.

Power tool cleaning to bare metal

SSPC-SP 11: power tool cleaning that removes all visible rust, mill scale and coating and leaves a surface profile, commonly at least 1 mil (25 µm).

Primer

The first coat applied to a prepared substrate, designed for adhesion and often corrosion inhibition, and to provide a sound base for subsequent coats.

Product data sheet (PDS)

The manufacturer's technical document listing a coating's properties, recommended surface preparation, mixing, application, film thicknesses, drying and recoat times. Also called a technical data sheet.

Proportioner

The metering unit of plural-component equipment that delivers each component at the correct ratio, pressure and, often, temperature.

Pull-off adhesion test

A test that measures the tensile force needed to detach a dolly bonded to a coating, reporting strength and failure mode. Covered by ASTM D4541 for metal and ASTM D7234 for concrete.

PVDF

Polyvinylidene fluoride, a fluoropolymer used mainly in factory-applied, heat-cured coatings for architectural metal. It provides exceptional UV, chalk and color resistance.

Ratio check

A test in which a plural-component proportioner dispenses each component into separate containers so delivered volumes or weights can be compared with the specified mix ratio.

Recoat window

The time interval, set by the manufacturer for given temperatures, within which the next coat can be applied with good intercoat adhesion. Exceeding the maximum may require abrading the surface.

Regulatory VOC

VOC content calculated excluding water and exempt compounds from the coating volume, as commonly required in regulations and labeling. It differs from actual (material) VOC, which uses total volume.

Relative humidity

The amount of water vapor in air as a percentage of the maximum it could hold at that temperature. Many coatings have upper limits, and some moisture-cure products have lower limits.

Relative humidity probe test

An in-situ concrete moisture test in which probes are placed in holes drilled to a specified depth and the internal relative humidity is measured after equilibration, per ASTM F2170.

Replica tape

A compressible foam tape burnished onto a blasted surface and measured with a spring micrometer to determine profile height; Method C of ASTM D4417.

Rust-back

Re-rusting of blast-cleaned steel before it is coated, typically caused by high humidity, condensation or soluble salts. It generally requires re-blasting.

Sacrificial anode

A more active metal, typically zinc, aluminum or magnesium alloy, connected to a structure so that it corrodes preferentially and provides cathodic protection.

Sagging

Downward flow of wet coating on vertical surfaces, forming curtains or runs. Causes include excessive film thickness, over-thinning and low temperatures.

Salt spray test

A laboratory test exposing coated panels to continuous neutral salt fog, per ASTM B117 or ISO 9227. It is useful for quality control but correlates poorly with many real environments.

Saponification

A reaction in which alkali, such as from fresh concrete, galvanizing or cathodic protection, converts oil-based binders like alkyds into soap, causing softening, stickiness and adhesion loss.

Scarifying

Concrete preparation using rotating cutters or flails to chip and groove the surface, producing medium to heavy profiles for thick overlays or removal of old coatings.

Secondary containment

A barrier system, such as a coated concrete dike or pit, designed to hold leaks or spills from primary tanks and prevent environmental release.

Shore hardness

A durometer measure of indentation hardness for elastomers and plastics. Shore A suits softer materials and Shore D harder ones, and it is commonly reported for polyurea.

Shotblasting

A machine method that propels steel shot at a surface and recovers it by vacuum for reuse. On concrete it removes laitance and creates profiles that vary with shot size, speed and number of passes.

Single-component (1K)

A coating supplied ready to use in one container. It cures by solvent evaporation, oxidation, moisture reaction or heat rather than by mixing with a separate hardener.

Sling psychrometer

An instrument with wet- and dry-bulb thermometers that is whirled in air; the two readings are used to determine relative humidity and dew point.

Soluble salts

Water-soluble ionic contaminants, mainly chlorides, sulfates and nitrates, left on surfaces. Even invisible amounts can cause osmotic blistering and underfilm corrosion.

Solvent

A volatile liquid that dissolves the binder and adjusts viscosity for application, then evaporates from the film. Solvent choice affects drying rate, flow and VOC content.

Solvent cleaning

SSPC-SP 1: removal of oil, grease, dirt, salts and similar contaminants with solvents, detergents, emulsions, steam or cleaning compounds. It is normally done before other preparation methods.

Solvent entrapment

Retention of solvent beneath a film that skinned over too quickly, often from excessive thickness or short recoat intervals. It can cause blisters, pinholes and softness.

Solvent rub test

Rubbing a coating with a solvent-soaked cloth and counting double rubs until softening or removal, to assess cure. ASTM D4752 applies this to ethyl silicate zinc-rich primers.

Splash zone

The part of an offshore or coastal structure intermittently wetted by waves and tides, typically the most corrosive exposure zone and requiring robust coating systems.

Spray-on bedliner

A thick, abrasion-resistant elastomeric coating, usually polyurea or polyurethane, sprayed into truck beds and onto equipment to protect against impact, wear and corrosion.

SSPC-PA 2

The standard procedure for determining whether measured DFT conforms to specified requirements, defining gauge readings, spot measurements, number of spots per area and acceptance limits.

Static mixer

A tube with fixed internal elements that repeatedly divides and recombines component streams, mixing plural components without moving parts.

Steel grit

Angular, hardened steel abrasive that produces a sharp, jagged surface profile. It is recyclable and widely used in shop blast rooms and recovery systems.

Stoichiometry

The balance of reactive groups between resin and curing agent, such as epoxide to amine hydrogen. Coatings are formulated near a target ratio to achieve full cure and intended properties.

Stripe coat

An extra coat, usually brushed, applied to edges, welds, corners, bolts and other hard-to-coat areas before or between full coats to ensure adequate film build there.

Surface-tolerant coating

A coating, often an epoxy mastic, formulated to wet and adhere to marginally prepared surfaces such as tool-cleaned steel with tight rust or old paint. Performance is generally below that over blast-cleaned steel.

Theoretical coverage

The area a given volume of coating covers at a specified DFT, assuming no losses. In US units, 1,604 × volume solids (as a decimal) ÷ DFT in mils gives ft² per gallon.

Thermal spray metallizing

Spraying molten zinc, aluminum or their alloys onto blast-cleaned steel by flame or electric arc to form a protective metal coating, often sealed and topcoated.

Thermoplastic

A polymer that softens when heated and hardens on cooling without chemical change. Thermoplastic coatings, such as many acrylic lacquers and vinyls, dry by evaporation and can be redissolved by solvent.

Thermoset

A polymer that cures irreversibly through chemical crosslinking and cannot be remelted. Epoxies, polyurethanes, polyureas and most powder coatings are thermosets.

Thinner

A solvent or solvent blend added to lower a coating's viscosity for application. Use only the type and amount permitted by the manufacturer, as excess can cause sags and VOC noncompliance.

Thixotropy

A property in which viscosity drops under shear, such as stirring or spraying, and recovers at rest. It helps high-build coatings resist sagging on vertical surfaces.

Tie coat

An intermediate coat used to promote adhesion between otherwise incompatible layers, such as old and new coatings, or between a primer and a specialty topcoat.

Tip size

For airless spray, commonly a three-digit code: the first digit is half the fan width in inches at about 12 in (305 mm), and the last two are the orifice diameter in thousandths of an inch.

Tooke gauge

A destructive inspection instrument that cuts a precise V-groove through the coating with an angled tip; a built-in microscope measures the thickness of each layer. Its method is described in ASTM D4138.

Topcoat

The final coat in a system, chosen for weathering, appearance, chemical resistance or other surface properties. Also called the finish coat.

Transfer efficiency

The percentage of applied coating that actually deposits on the target. It is typically higher for brush, roller, electrostatic and HVLP application than for conventional air spray.

Two-component (2K)

A coating supplied as a separate base and curing agent that react chemically after mixing. Most epoxies, polyurethanes and polyureas are two-component.

Undercure

Incomplete curing that leaves a coating soft, tacky or chemically weak, usually from off-ratio or poor mixing, low temperature or incorrect film thickness.

Undercutting

Corrosion that spreads beneath a coating from a scribe, edge or defect, lifting the film as it advances. Also called rust creep.

Vinyl ester

A thermosetting resin with an epoxy-derived backbone and methacrylate end groups, cured by free-radical reaction. It is used for highly chemical-resistant linings, often glass-flake or fiber reinforced.

Volatile organic compound (VOC)

An organic compound that evaporates and participates in atmospheric photochemical reactions forming ground-level ozone. Coating VOC content is regulated and expressed in g/L or lb/gal.

Volume solids

The percentage of a coating's wet volume that remains as dry film after volatiles evaporate. It links wet to dry film thickness and determines theoretical coverage.

Waterborne coating

A coating that uses water as its main carrier, as a latex dispersion or water-reducible resin. Most have lower VOC content but are more sensitive to cold and high humidity during cure.

Waterjetting

Surface preparation with high- or ultra-high-pressure water, defined by joint SSPC/NACE WJ standards. It removes coatings and soluble salts but does not create a new profile, instead re-exposing the existing one.

Wet film gauge

A notched comb-style gauge pressed into wet coating; the highest tooth wetted indicates wet film thickness, as described in ASTM D4414.

Wet film thickness (WFT)

The thickness of a coating immediately after application. Target WFT equals the required DFT divided by volume solids, adjusted for any added thinner.

White metal blast

SSPC-SP 5/NACE No. 1: blast cleaning to a surface free of all visible oil, grease, dirt, mill scale, rust, coating, oxides and foreign matter, with no staining. Roughly comparable to ISO Sa 3.

Wrinkling

A puckered, ridged surface formed when the top of a thick film cures faster than the layer beneath, common with oxidative-cure coatings applied too heavily or in heat.

X-cut test

An adhesion test in which an X is cut through the coating, tape is applied and removed, and detachment is rated; ASTM D3359 Method A, used for thicker films.

Zinc-rich primer

A primer heavily loaded with zinc dust that protects steel galvanically, with the zinc corroding preferentially at damage. Binders are organic (typically epoxy) or inorganic (typically ethyl silicate).