A sharp edge at the meeting of two surfaces at an angle with one another.


Discolouration of a coating by diffusion of natural timber extractives, or previous coatings such as bitumen based products.


A hazy bloom to the coating surface, much like the bloom on a grape. Often associated with a reduction in gloss level.


Unwanted adhesion between adjacent surfaces of articles that develops when these surfaces are left in contact.


Milky opalescence which sometimes forms as a varnish or woodstain dries


Build is the visual impression of the coating thickness of a dried film. Classification of build based on the measurement of the dry film thickness according to method 5A of ISO 2808 : 1991 is as the following categories:

Minimal build:

mean thickness less than 5µm

Low build:

mean thickness 5µm up to 20µm

Medium build:

mean thickness greater than 20µm up to 60µm

High build:

mean thickness greater than 60µm


Areas of a wet film where the coating material recedes or ‘pulls away’ from the surface.


Areas of a wet film where the coating material recedes or ‘pulls away’ from the surface leaving circular gaps in the film.


Areas of a wet film where the coating material recedes or ‘pulls away’ from the surface.


Loss of adhesion between applied layers of coating, or between the coating and the underlying substrate.


The breakdown of the timber substrate as a result of prolonged exposure to sunlight and rain, resulting in a loose and fibrous surface.


Loss of the natural extractives from the timber surface through exposure to sunlight and rain, resulting in greying and bleaching of timbers.


To remove, by use of a fine abrasive, small raised areas or particles of foreign matter which stand proud on the surface of a coating film, without breaking through the surface coating.

Durability (natural)

The inherent resistance of wood to attack by wood destroying organisms. The term ‘durability’ used with reference to the classification for heartwood, according to BS EN 350-2 : 1994. The majority of sapwood in commercial use is deemed to be Class 5 (Not Durable)

Durability class 1:

Very Durable

Durability class 2:


Durability class 3:

Moderately Durable

Durability class 4:

Slightly Durable

Durability class 5:

Not Durable


White powdery substance on the surface which is the result of soluble salts within the substrate migrating to the surface.


The ability of a coating to stretch with the substrate as it swells or shrinks.


Substance which is not part of the cellular structure of wood and can be dissolved out.


Substance which is formed within the cell structure of wood and is mobilised by heat.


Areas of a wet film where the coating material recedes or ‘pulls away’ from the surface leaving circular gaps in the film.


Pigments form globules due to non-uniform pigment dispersion and spots of colour are noticeable.


The underlying substrate shows through the most recently applied coating. This can happen with an opaque coating, or with a woodstain system if the existing coating/timber and the top coat differ greatly in colour.


The central core of a tree, consisting of non-functioning tissue which is rich in tannins/extractives. The heartwood is often darker than the outer sapwood and generally denser and less absorbent.

High build

See ‘Build’

High Solids

A term applied to coating materials in which, by the choice of suitable ingredients, the content of volatiles (solvents) present is kept to a minimum, consistent with the maintenance of satisfactory application properties.


Permanent reminder of the point where branches began to grow from the trunk of the tree

Low build

See ‘Build’

Medium build

See ‘Build’

Minimal build

See ‘Build’

Moisture Vapour Permeable

Often termed ‘microporous’, the property of a coating to allow the passage of moisture in the form of vapour, not liquid, into and out of the substrate.


See Moisture Vapour Permeable.


Not translucent or transparent, i.e. a coating which will obliterate the colour of the underlying surface to which it is applied.

Orange Peel

The surface of the dried coating film resembles the skin of an orange. This effect is often the result of the use of a roller for the application of a coating, particularly if it is rolled out thinly and unable to level out to a smooth film.

Runs or Sags

Movement and tears of coating soon after application to vertical substrates. In severe situations, also known as ‘curtains’.


The outer wood in a tree, just beneath the bark in tree trunks. This is the living tissue in a tree.


This refers to products in which the main solvent carrier is an organic solvent, usually white spirit.


Allowing light to pass through partially. In terms of a coating, a translucent or semi-transparent coating is one through which the underlying substrate remains partially visible.


Product in which the main solvent carrier is water.


A term used to describe the surface finish of a dried paint film having the appearance of a wrinkled and aged skin. This is the result of excessive thickness of coating so that the surface dries, forming a skin, while the coating remains wet beneath.


Volatile Organic Compound. Definition – Any organic compound with a boiling point (or initial boiling point) lower than or equal to 250oC, at normal conditions of pressure, which participates in atmospheric photochemical reactions.