A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Abrasion resistance

Ability of a coating film to resist the impact and friction caused by abrasives.

Abrasive

Substance suitable for carving and eroding, due to its hardness and shape. Used to smooth bare wood or basecoat before coating.

Abrasive sponging

Procedure for removing defects of a surface by fibrous, metal or synthetic abrasive materials.

Accelerated weathering

Artificial and accelerated aging of the coated item. Special equipment that reproduces the conditions of natural outdoor exposure, such as sun and rain, is used to test the life of the coating film. This equipment can simulate long-term conditions in few days/hours.

Adhesion

Resistance exhibited by a dry coating film to the action of detaching it from the wood surface or from an underlying coat of coating.

Airless

See Spray gun.

Airmix

See Spray gun.

Ambient humidity

Relative humidity of the coating environment, which should not exceed 85%.

Antique stain

Stains applied onto basecoats and rubbed away with Scotchbrite or wire wool to produce special effects of shading into moulded or grooved areas, giving an antique appearance to the piece of furniture.

Application methods

Adaptability of a coating to a given coating system.

B

Bactericide

Chemicals that protect coating and wood from the action of micro-organisms.

Basecoat

This is also called sealer and has the following functions:
1) Filling the wood pores
2) Allowing sanding, preserving the item colour
3) Realising a good bonding of any other basecoats or of the topcoat, thanks to "micro-streaks" caused by sanding.
A properly chosen and applied basecoat is critical for the final result of the entire coating system. Based on the user’s needs and on the desired result, it is possible to apply one or more basecoats. A basecoat may be single-component (as with nitrocellulose and waterborne ones), two-component (as with polyurethane ones) and multi-component (as with polyester ones).

Basic weight

Quantity of coating to be applied, expressed in grams/m2 (g/m²).

Binder

Solution or dispersion of resin in a solvent or water. This is usually added to stains to enhance certain features (e.g. pore marking) to prevent over-absorption and bleeding.

Bleaching

Defect of a coating caused by the incorporation of dampness and/or air while drying, or by a partial detachment from the support, or by the separation of one or more components of the coating. It can be caused by heat or by atmospheric agents.

Bleaching (of wood)

Treatment usually carried out with hydrogen peroxide and ammonia to remove dark stains and spots and lighten the colour of wood.

Bleeding

Phenomenon which occurs when the dyes of a stain are re-dissolved by the basecoat applied on it, leaving dark spots on the surface. To prevent bleeding, the colours used over the basecoat should be resistant to its solvents.

Blistering

A defect that occurs when small blisters appear during drying if solvent or air are trapped in the film, or if chemical drying is inhibited by substances contained in the substrate.

Blocking

Phenomenon that occurs when two coated surfaces in direct contact at high temperatures and pressure stick together.

Bonding

Adherence between a coating film and the underlying material to which it is applied.

Brittleness

Tendency of a dried film to crack or flake when bent or scratched. It is the opposite of elasticity.

Brush

Tool for the manual application of coatings suitable for this method. It consists of a support provided with a handle on which bristles or fibres (either animal or synthetic) are set.

Brush rollers

Cylinders with a central axis to which filaments of different nature are fixed. Those made of natural or vegetal fibre bristles are used to remove excess stain (not dried yet) and obtain the so-called "tear effect". Nylon abrasive ones are used for dry-sanding basecoats. Those for polishing polyurethane or polyester coatings are made up of cylinders covered with tightly tied cloth rings. Polishing is carried out using abrasive waxes or pastes.

Closed pore

"Closed pore coating" denotes an application of coatings that completely fills the wood pores.

C

Casings

General term used to denote all types of frames and relevant accessories. A distinction must be made between casings installed in a house and those installed outdoors, for obvious different requirements as regards weathering protection.

Catalysis ratio

Incorrect term indicating how much hardener must be added to 100 parts of coating to obtain the cross-linking in two-component products.

Chalking

Condition that occurs when loose powder forms on the surface of a dried film. It is caused by the deterioration of the binder and is usually observed on outdoor exposure.

Charge

Substances used to change the chemical-mechanical resistance features of coatings. Insoluble in binders like pigments, on the other hand they exhibit no covering and colouring effect.

Chip board

Agglomerate of wood particles bonded by special glue and pressed to obtain flat surfaces (commonly called chip board panels).

Cissing

Defect of a coating film that occurs when the substrate is contaminated by incompatible chemicals around which the coating "withdraws" leaving some parts of the underlying substrate uncoated. This defect is generally referred to also as "cratering" or "fish eye".

Coalescent

This is a solvent for the water-dispersed polymer belonging to the glycol-ether family. It is added to water-based coatings to help the film formation at ambient temperature. The average coalescent percentage contained in a water-based coating is 2-5%.

Coating

Term used to denote non-pigmented coatings.
They are divided into various families, of which the main ones are:
-Waterborne coatings
-Nitrocellulose coatings
-Polyurethane coatings
-Polyester coatings
-Synthetic coatings
-Acid cured coatings
-Acrylic coatings
-UV coatings

Coating application

There are different types of coating based on the application method used.
- Flow-coating: jet spraying of a coating, in a larger quantity than what required, which is made to drip, recovered and put into production again.
- Dipping: application by dipping the item to be coated into a tank, extracting it at a controlled speed to obtain an even coating.
- By brush: manual application by brush.
- By roller: See Roller.
- Spray: application of coating sprayed by gun or similar tool.
- Airless, see Spray gun.
- By cloth: manual application with a cloth soaked with product.
- By pad: see Pad.
- By extrusion: a wooden profile is made to pass in a coating bath contained in a special tank: the amount depends of the accuracy of an outline through which the outcoming profile passes.
- By vacuum extrusion: unlike the conventional extrusion, this uses a vacuum to determine the thickness, specific for UV coatings.
- By plunging: manual coating that differs from the dipping coating in that the extraction speed is not controlled.
- By fog coating: application of a coating fog that lays onto the item to be coated (arranged on a conveyor belt) falling from a head transversal to the belt.
- With reverse: See Reverse roller coater.
- Electrostatic: application performed by an electric field created between the spraying system and the item to be coated. See Spray gun.

Coating cycle

All the operations required to paint timber, which could be exemplified as follows:
1) Staining/priming (or finishing) of the timber by stains/primers to make it of the desired colour and, in case of priming, to protect it from fungi.
2) Application of the basecoat(s) or sealer.
3) Sanding.
4) Application of the topcoat, which may be clear or pigmented, gloss or with various level of opacity according to the version.

Coating porosity

Defect of a coating film consisting in the presence of microscopic pores that reach the wood.

Coating product

Liquid or powder product that when applied on a support forms a film exhibiting protective, decorative and/or special technique qualities. It can be single - or two-component (if a cross-linking or hardening agent is required for hardening).

Cold-check

Ability of a coating film to resist to high and low temperature cycles without cracking. It is expressed with the number of cycles it can undergo.

Compatibility

Ability of two or more coating products to mix with each other.

Conditions for good painting

The environment must be free from dust and contaminants, with a temperature between 18 and 24°C and relative humidity from 40% to 75%. The wooden item must have a temperature between 18 and 22°C and relative humidity from 8% to 14%. The coating system must be chosen in accordance with the type of item. The viscosity must be suitable for the application system. The mixing (in two or more-component products) must be done according to the proportions indicated by the coating manufacturer. The items must be well prepared (sanded, cleaned and reduced, if intended to be worked on line). The drying tunnel, when available, must be at the required temperature. The application equipment (guns, pumps, pipes, fog coating devices) must be perfectly clean, in particular the compressor air must be dehydrated and oil-free. The coating must be well stirred before application.

Conductivity

Ability of a coating to conduct electric charges, inversely proportional to resistivity. This characteristic is used in the electrostatic application of coatings.

Covering

Feature of the coating to cover the support’s irregularities and especially the sanding pores and streaks.

Cracking

Defect of a coating film resulting in breaks on its surface and/or in depth. It may be caused by:
- movements of the substrate that the coating film cannot stand;
- excess of hardening agents resulting in too fast drying and/or too brittle dry film;
- solvents still present in UV coatings when they are passed under UV lamps for immediate curing;
- improper coating cycle (failure to observe the drying times or use of coatings other than those recommended).

Cratering

See Cissing.

Cross-linker

Additive to be added in percentages of 0.5-1.5% to waterborne coatings to improve their chemical resistance (e.g. to water, alcohol, coffee, oil, etc.). It acts by creating bonding bridges between the various chains of the polymer.

D

Density

Weight of a unit volume of a matter, normally expressed in grams/cm³ or in kg/dm³. In everyday language, the term specific weight is often wrongly used as synonym.

Dipping

See Coating.

Direct gloss

Procedure that allows obtaining a glossy surface without polishing. This reduces the processing time but requires expensive equipment (pressurised booths, suitable filtering systems, etc.) and very accurate control of temperature, air humidity, etc.

Drying

Phase during which volatile components (thinners, solvents, waters, coalescent) evaporate and the resin start to polymerise; it may occur: at room temperature, with hot air (30°C-60°C), with UV lamp or IR rays.

Drying carousel

A driven course of coated panel bearing trucks in a hot air tunnel, up to 60°C

Drying time

Coating film drying time.

Dust free

Stage of the drying process when dust does not stick to the film anymore

E

Elasticity

Ability of a coating to return to the shape it had before being subject to deforming stresses, without cracking.

Emulsion

A stable suspension of fine particles of a fluid or a polymer in another fluid whichfluid, which is not normally miscible with the first one. Typical examples are acrylic coatings in aqueous emulsion.

F

Fibre raising

Phenomenon caused by the contact between the water or solvent contained in the coating and the wood fibres, thatfibres that therefore tend to raise.

Filler

Product used for filling irregularities of the wood to be coated, with a high filling power and good sandability.

Film

Thin layer of coating.

Fire retardant

Fire retardant
Term defining a coating suitable for delaying combustion of the substrate on which it is applied, forming an insulating layer that restricts and delays the substrate’s heating.

Flaking

Detachment of a coating film from wood or from an underlying film in the shape of flakes

Floating

Defect that occurs when during drying, one or more components rise to the surface.

Flow-coating

Application of coatings by jet sprinkling, with the same results as dipping, but with the advantage of using less material and facilitating the colour change. See Coating.

Fog coating machine

This machine emits a continuous fog of coating below which the items to be coated pass at programmed speeds.

Fungicide

A substance generally contained in the primer that protects the wood from the action of moulds and fungi.

G

Gloss

Reflecting power of the coating towards the incident light. See Gloss degree.

Gloss degree

It indicates, in percentage, the ratio of incident light specularly reflected by the painted surface. It ranges between 0 (minimum gloss = no specular reflection of the incident light) and 100 (maximum gloss = specular reflection of the incident light); it should be noted that these values are purely indicative.
Normally, the gloss degree of a coating is indicated with commercial terms, as follows:
- Deep mat = 1 to 10 gloss degrees
- Mat = 11 to 30 gloss degrees
- Medium mat = 31 to 40 gloss degrees
- Semi mat = 41 to 50 gloss degrees
- Semi gloss = 51 to 80 gloss degrees
- High gloss = from 81 gloss degrees on

H

Heads

They form during the drying stage, when solvent and air cannot come out of the film that has generated an already hardened film on the surface.

Humidity

Humidity rate of the wooden item to be coated, which should range between 10% and 14% maximum, to allow a perfect filming of coating products

I

Impregnant

Liquid coating product that penetrates in the wood pores, changing the characteristics of the surface without forming a film. It is used to protect the wood from moulds and fungi and in the coloured versions, to reduce the destructive action of solar radiations.

Impregnated paper

Artificial veneer consisting of a paper film, impregnated with resin. They can be of one colour, or copy wood grains and colours

Incompatibility

Coatings, products or substances that cannot be mixed. Usually results in the separation of solid particles or turbidity of the mixture. It occurs when a product cannot be mixed with another one. Various defects occur during and after the application

Intrados

The door frames to which the casings are hinged.

IR lamps

Lamps whose heat is used to speed up solvent evaporation and favour the drying of coats, and in particular of solvent coatings.

L

Life

See Spray gun.

Light fastness

Ability of a coating or of a coated timber to retain its original colour when exposed to light. Sunlight, and particularly its UV part, can alter the colour of natural wood and stains, producing yellowing of timber, and discoloration of stains. The presence of anti-oxidants and UV absorbers slow down yellowing and discoloration. Also pigmented coatings (especially white) are sensitive to yellowing over time. Light fastness can be further increased by choosing appropriate hardeners, or special coating families (such as acrylic-polyurethane coatings). Yellowing resistance Ability of the coating film to retain its colour under the action of light. Yellowing usually refers to white lacquered coatings.

M

MDF (Medium Density Fiberboard)

Agglomerate of fine wood particles bonded by special glue and pressed to obtain flat surfaces. Compared to chipboard (see) Medium Density Fiberboard is easier to coat and exhibits a higher chemical-physical resistance.

Mixing

A process through which two or more components of coating products, suitably blended, start to cross-link, that is, to become hard to form the solid film. In mixing it is important to observe the prescribed doses for the various components and the process time of the mixed part. See Pot-life.

N

Neutral

A colour is neutral when it is neither clear not pigmented. A neutral coating applied on a wooden surface forms a film with an opalescent effect that lets you catch a glimpse of the wood as if it were dimmed. Neutral coatings are normally used as bases for pigmented lacquers.

O

Opacity

Non-reflection of the incident light by the coat film. See Gloss.

Open pore

"Open pore coating" denotes an application of coatings that does not completely fill the wood pores, keeping their outline also at the end of the cycle.

Orange peel

Surface defect consisting in the dimpled appearance of the dry coating film resembling the peel of an orange.

Oven

Plant for forced drying of coatings. See Drying which is the most important element for distinguishing the main types of ovens.

Overspray

In spray applications, quantity of coating that does not fall onto the item to be coated and is therefore wasted, with ensuing environmental and economical disadvantages

P

Pad

Cloth containing a mass of wool or cotton threads which, conveniently soaked, is used to coat antique furniture with proper coating.

Paint

A term that generally denotes a pigmented coating that is applied to a support and forms a covering film.

Photoinitiator

Compound that following the exposure to ultraviolet light is capable of releasing substances that activate polyester and acrylic UV coating polymerisation reactions.

Photostability

Ability of a coating to preserve its colour if exposed to light.

Pigments

Coloured substances that give the dried film the desired chromatic effect (they can be both organic or inorganic and are not soluble in solvents). In the practice, when added to a clear coating, they give it both colour and hiding power.

Pigments

Coloured substances that give the dried film the desired chromatic effect (they can be both organic or inorganic and are not soluble in solvents). In the practice, when added to a clear coating, they give it both colour and hiding power.

Pin holes

Defects of a dried film, which results in small holes in the film.

Polishing

Operation intended to remove dust particles from the surfaces using fabric or fibre brushes.

Pore bypassing

Defect of a coating that does not penetrate into the pores but remains along its edges, thereby impairing its flow.

Pot-life

Period of time within which it is possible to apply the coating, before polymerisation causes a viscosity increase which makes application impossible.

Pre-compound

A veneer of natural woods obtained by gluing rotary-cut veneers to one another. Different grains are obtained with differently angled cutting surfaces.

Pre-stained

A veneer already stained by the manufacturer.

Pressurisation

Treatment of the air of a coating workshop, with filtering of the inlet air, whose pressure is higher than ambient one. This is performed to purify the air from dust particles.

Pricks marking

Defect of a coating film caused by the presence of granules on the surface.

Primer

Defect of a coating film caused by the presence of granules on the surface.

Print- free

Drying time after which when a light pressure is exerted on the coating film, no stickiness is felt

Profiles

Term that generally refers to an item with a prevailing linear dimension, variedly shaped.

Pulling up

Defect that is found on not perfectly seasoned woods, consisting in the raising of the fibres following the action of aqueous products.

R

Radical catchers

Chemical usually added to topcoats that block the ultra-violet rays of the solar spectrum before they reach the substrate. Addition of UV absorbers enhances wood protection and provides longer service life of the coating film.

Removal

This phenomenon occurs when the topcoat solvent penetrated through the basecoat into the wood pores, damages the basecoat and raises it, thus producing swelling.

Retardant

Generally a high-boiling solvent that delays the film forming process and helps the film flow

Reverse roller coater

This machine is made up of two rollers (spreading roller and gripping roller) that rotate in opposite direction, thereby allowing more spreading evenness.

Roller

There are two roller applications:
1) Roller coater in automatic coating lines, made up of a pair of two rollers, a spreading and a gripping one. By changing the pressure of the spreading roller on the wood, as well as its speed, the basic weight of the product applied changes as well.
2) Revolving brush for the manual application of coatings, suitable to be used on flat surfaces. Consisting of a cylinder covered with synthetic or natural bristles rotating on the central pin fixed to the handle.

Running

Drips occurring during coating application on vertical items. It is usually due to: excess coating, too fluid product, lack of thixotropy.

S

Sanding

Operation carried out using sandpaper or other abrasive to prepare the bare timber for the first coat of paint or the base coat for the topcoat. In some coating cycles it is possible to carry out sanding operations also on the impregnant or on intermediate applications of base coats.

Sandpaper

This is used for sanding timber to be coated or to sand previously applied coats of paint. This material is in the form of grains of different size, defined by a number that denotes the number of meshes in a square inch (6.45 cm²) of the sieve, through which abrasive grains identified by such number have passed. The following table shows the most common sand paper types:
                    Paper grit                Definition
                  40 - 60 - 80            Very coarse
                100 - 120 - 150            Coarse
                 80 - 200 - 240             Medium
                280 - 320 - 360              Fine
                400 - 500 - 600           Very fine
                700 - 800 - 900           Ultra fine

Scaling

Detachment of the coating film from wood, in the shape of scales, following cracking.

Scotch-Brite

Abrasive lapping wheel used to sand profiles.

Sealer

Basecoat or primer applied to the item to prevent substances from passing to the following coating layers. It also denotes a product to apply to difficult items, such as melamine papers, plastic sections, special woods, etc., as preparation for a normal system.

Self-priming

This is the ability of the waste formed in the application of synthetic coatings of self-priming. This phenomenon is favoured by an ambient temperature of more than 25-30°C. Always avoid using dry booths and at the end of a working day, move the waste outdoors, collecting it into open-air drums filled with water.

Shading

See Stain retouch.

Shrinkage

Contraction of a coating film during the drying process.

Smoothness

Pleasant touch of a coated surface felt by passing the hand’s back on it.

Solid content

This is the percentage of non-volatile matter of the coating that remains on the film after drying. A high covering is obtained with more than 40% of solid content; 35%-40% gives a medium-high covering, while less than 35% gives a medium-low covering. The solid content is generally low for open-pore coating systems, high for closed and semi-closed pore ones.

Solvent

Liquid that dissolves and keeps the resins in solvent coated products in solution. It reduces viscosity and helps application and flow of the coating. It completely evaporates during drying.

Solvent

Liquid that dissolves and keeps the resins in solvent coated products in solution. It reduces viscosity and helps application and flow of the coating. It completely evaporates during drying.

Solvent-based coatings

These coatings are soluble in solvents, and dry up very quickly compared to water-based coatings. Unlike the latter, they cause colour changes based on the amounts applied on the support.

Specific weight

Weight of the volume unit of a material. Since the weight of a material is given by its mass multiplied by acceleration, unlike density, the specific weight changes with the acceleration. So, while density is a comparable value, specific weight is only acceleration being equal (gravity acceleration varies according to altitude and latitude).

Spray booth

Plant in which coating is sprayed. It can be open (if without roof and walls) or closed (if provided only with opening for the passage of work pieces). According to the direction of airflows, it may have vertical, oblique or horizontal ventilation. Moreover, it can be air-conditioned or pressurised (see Pressurisation). Based on the removal of excess paint particles, it can be humid (e.g. water screen) or dry (e.g. filters).

Spray gun

Tool used to spray the coating. It is available in several versions differing in their construction features and in the type of atomization used. They can be manual and for individual use, or mounted on supports, fixed or program-operated, or robot-controlled.
The main types of guns are:
- Traditional air spray with cup.
- Air gun with under-pressure nozzle.
- Airless, for airless spraying of the atomized moisture at medium-high and high variable pressures (about 120 to 250 atm.).
- Airmix: to spray at intermediate atomization conditions, between air and airless.
- Electrostatic, air, or airmix spray gun that uses the attraction between the item to be coated and the coating, which is given an electric charge opposite to that of the item itself of.
- HVPL (High Volume Low Pressure): they use a large low-pressure air volume to atomise the product; this allows several advantages related to both the enhanced efficiency of transfer and to the improved finish quality.

Spreading rate

Number of square metres that may be coated with 1 kg of ready to use coating.

Stackability

Drying time required for stacking coated items without marking or sticking.

Stain retouch

Operation that colours spots where an excessive sanding has removed the basecoat, by applying a specific stain on an already sanded basecoat. This process is used to balance any differences of colours found after the basecoat application.

Stratification

Lack of adhesion between different applications of the same coating product.

Substrate

Synonym of ''Support''. Another term to indicate a surface to be coated.

Support

Any solid surface intended to be coated.

Surface hardness

Resistance exhibited by a coating to mechanical stresses (scratches, impacts, friction, pressures, etc.).

Swelling

Alteration of a coating film following the absorption of liquids and vapours.

T

Thermo-hygrometer

Instrument consisting of a thermometer and a hygrometer to respectively measure the temperature and the relative humidity of the coating environment, also called environmental factors (see conditions for good painting).

Thickness gauge

Easy to use instrument that measures the wet thickness of coating when applied.

Thinner

Fluid that changes the coat viscosity and drying time to improve its application and help the film flow. Specific thinners should be used for each type of product due to compatibility reasons. Thinners are characterised by solvency (ability to decrease viscosity of the coating), speed of evaporation, resistance and ability to increase the pot life. Each type of coating requires specific thinners (polyurethane coatings require alcohol-free thinners with less than 0.5% water). The choice of a proper thinner, which also depends on the application method, is very important to obtain a perfect result.

Thinning ratio

Quantity of thinner expressed in parts (by weight and volume) that is added to 100 parts of a coating to bring it to the desired application viscosity.

Thixotropy

Property of a coating to be applied on vertical items without running.

TLV

Threshold limit value of the substances, indicated at item 8 of the Sayerlack Material Safety Data Sheet. It indicates the concentrations in p.p.m. (parts per million) or mg/m³ of the substances dispersed in the air at which most workers can be exposed repeatedly without negative effects on health: the higher the TLV, the more hazardous a substance.
TLV-TWA: threshold limit value - time weighted average.
TLV-STEL: threshold limit value - short time exposure limit.

Topcoat

Final coat applied in the coating cycle. It can be clear or pigmented and gloss or matt.

Transparency

Ability of a coating not to hide the appearance and the colour of a substrate.

U

UNI

Standards among which several relate to the tests for assessing the quality of the finished surface of coated products. UNI EN standards are acknowledged at a European level.
For further information, see www.uni.com.
UNI EN 12720 Evaluation of surface resistance to cold fluids.
UNI EN 12721 Evaluation of surface resistance to damp heat.
UNI EN 12722 Evaluation of resistance to dry heat.
UNI 9115 Surface behaviour to abrasion wear.
UNI 9149 Determination of the surface specular reflection.
UNI 9241 Determination of surface resistance to cigarette action.
UNI 9300 Determination of surface tendency to retain dirt.
UNI 9427 Determination of surface resistance to light.
UNI 9428 Determination of surface resistance to scratching.
UNI 9429 Determination of surface resistance to sudden changes of temperature.
UNI EN 71-3 Safety of toys. Migration of some elements

UNI Standards

See UNI.

UV absorber

Chemical usually added to topcoats that block the ultra-violet rays of the solar spectrum before they reach the substrate. Addition of UV absorbers enhances wood protection and provides longer service life of the coating film.

UV lamps

Lamps emitting radiations that are capable of hardening some types of resin-based coatings such as unsaturated polyester and acrylic coatings, etc.

V

Vacuum

Priming method especially suitable for casings, consisting of the following steps:
1) Negative pressure in autoclave to remove most of the air from the wood intercellular gaps.
2) Inlet of the priming product in the autoclave, which gradually reaches the atmospheric pressure, thereby helping the primer penetration, due to the difference of pressure produced by the previous vacuum treatment. The intercellular gap vacuum helps a deep penetration.
3) Emptying of the autoclave and final vacuum, which is higher than the first stage and therefore helps the exit of excess primer.
4) The item is returned to atmospheric pressure, which causes a return of the primer still on the surface, with consequent drying of the same.

Verticality

See Thixotropy.

Viscosity

Fluidity degree of a coating whichcoating that can be modified by adding solvents. It is very important for coating workability, according to the application method used: it is usually low for spraying, immersion or flow coating, medium for curtain coating and high for vertical spraying and roller coating. It is usually measured by "DIN CUP" viscometers. These viscometers are 100 cm³ cylindrical containers with a conic bottom provided with a 2, 4 or 8 mm hole. For example, if the diameter is 4 mm, the cup is called DIN no. 4. The cup is filled with coating and its discharge time expressed in seconds is the measure of viscosity. The discharge time (= viscosity) must be measured by a chronometer. Since viscosity is affected by test temperature, viscosity values in technical data sheets usually refer to a standard measurement temperature of 20°C.

W

Waterborne coatings

These coatings are thinned in water, which has a high affinity with wood and therefore enhances its grain and hues, thanks to its deep penetration. They can be applied by dipping, cloth, spray, and flow-coating. In the brush application, the excess of coating must be removed by a dry brush, a sponge or a cloth, according to the grain direction.

Weathering resistance

Resistance of the coating film towards the erosion and corrosion of atmospheric agents. This characteristic varies according to the wood and coating used, based on the item installation place

White pores

Defect of a coating (nearly always due to the detachment of the film from the substrate) causing white-silver spots between wood and coating.

Whitening (of a coating)

See Bleaching.

Wrinkling

Defect of a coating occurring when a film dries on the surface more quickly than below a surface.