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News Story

Wood Flooring Technical Terms explained


Many people are unfamiliar with terms used in a particular industry, this blog is intended to help explain these phrases in a simple way, please let us know if you have any comments on these. There are a few blogs with separate headings on different aspects of wood flooring and fitting.

Timber, wood flooring and the terms used in its construction from tree to unfinished floor – if you need further professional advice, please call our experts here at the Solid Wood Flooring Company on 01666 504015.

Air Drying

This is the traditional method of drying timber which occurs over a few years and is otherwise called Seasoning. This however will not normally reduce the moisture content below 15% depending on how it has been seasoned and the humidity levels at the time.

Kiln Drying

We need a moisture content of 8% to 10% for wood flooring in the UK not to move excessively once fitted, this is achieved by kiln drying which is like a big oven in which the temperature, humidity and movement of the hot air is controlled. This means that the wood flooring we produce is kiln dried to BS8201. If a floor is fitted in a very hot climate where humidity is low then it could reduce the moisture to 5%, which means that you will get gaps appearing on the wood flooring. This can also happen if you have hot spots with underfloor heating.


This is where we bond one material such as a solid layer of oak on the top of a multilayer plywood board. The level of adhesion will be affected by the conditions of the surfaces of the timber to be coated with an adhesive, the closeness of the contact and temperature and humidity at the time. We control the environment where our engineered boards are made

Bevel Edge and Micro Bevel Edge

This is a feature in the manufacture of wood flooring whereby the sharp edge of the board is taken off and the bevel clearly defines the floor board edge (which can be more than 2mm) which can add to the ambience of the room it is installed in. The bevel edge is normally angled at 45 degrees. The micro bevel edge will be 0.5mm to 1mm so it is hardly visible but does leave a definition between each floor board once it is laid.


This process is used to lighten timber and is normally a VOC free chemical. All natural wood will bleach with direct sunlight especially Walnut and Maple.

Dark Brown Oak

This is oak that has a dark chocolate colour and has turned brown due to a fungal infection that causes a chemical change in the tree, this happens a lot in English Oak.

Parquet Wood Blocks

These are small pieces of timber in sizes that range 70mm x 250mm or 90mm x 350mm in varying thicknesses, our blocks are 8mm thick as we fix them direct to a plywood sub floor. The old traditional parquet blocks were 20mm to 22mm thick and fixed to a concrete floor using bitumen. The problem here is that they often lift and it is difficult to replace.

Floor Boards (planks and strips)

This is the finished wood flooring which can be from 60mm to 200mm wide in solid boards and up to 340mm wide in engineered boards. Solid floor boards must never be floated as they will expand and contract too much.

Janka Test of Brinell Hardness Test

This is a hardness scale of different species of timber and the higher the number on the janka test the harder the wood flooring. Strand Woven Bamboo is one of the hardest flooring options available and is also the greenest option helping our environment.

Case Hardening

This is where wood has been kiln dried incorrectly. It can never happen with naturally seasoned timber. If timber is dried too quickly the surface shrinks very heavily which then compresses the interior of the tree which still contains a lot of moisture. You can find that cheap wood flooring has been subjected to fast drying which means that when fitted the flooring is likely to split, warp and move excessively.


Cellulose is a long-chain polymeric polysaccharide carbohydrate, of beta-glucose . It forms the primary structural component of green plants. It forms the cell walls and framework for trees to grow and thrive.


This is a separation of the wood fibres lengthways which extends across the rings of annual growth. This usually results from stress within which occurs when wood seasoned.

Click System

This is a method of joining floor boards together without using any adhesive. There are several patents and systems and it is where you need to put the boards together at and angle and then “click” them into place so that they stay together. This should not be used with solid boards and is normally associated with the cheap poplar softwood engineered boards.

Close Piling

Stacking of wet timber without sticks for air circulation (not kiln drying) which results in staining of the timber and serious losses due to fungal decay.

Coefficient of Expansion

Any natural product especially timber will expand and contract with changes in humidity and moisture. The rate of change will depend on the porosity of the wood and how well it has been dried. The rate of change, which will depend on the species of timber can be measured by producing a table with test results. We have all these results in our technical specification document. The change in width can happen when moisture goes from 10% to 20%. For example Beech has a high coefficient whereas oak has a low one. Oak is a very stable wood floor especially and engineered wood floor and this link will explain more.


Health and safety is a very important issue these days and you can see more on our web site. We do not use VOC in our production and all our wood flooring is produced in accordance with the control of Substances Hazardous to Health.

Conditioning and Balancing

We use a special type of kiln to balance all the wood flooring we produce so that the moisture in the different layers is all the same to create an equilibrium in the flooring.


This can be a small or wide gap in the timber normally caused by the wood shrinking or where we have a shake which is a defect in the board. Shakes as they are known can increase in size if the timber has not been kiln dried properly or if it is from an old tree that has not been processed properly. You can see obvious shakes in old green oak gate posts for example.


This is where the floor boards distort towards the inner rings of the tree so that the surface becomes convex usually caused by humid or damp conditions on solid wood flooring.


Similar to the above but where the boards distort and the surface become concave. This always happens if there is damp or moisture below the floor so that the bottom surface becomes saturated with moisture and expands and the top surface is still dry with a lower moisture content. Once cupping takes place it is unlikely that the board will flatten out again but there could be some movement in the future if the bottom dries out or the top surface takes in moisture.

Shrinkage Differential Problems

Wood flooring that come from different trees of the same species can shrink and expand at different rates due to the individuality of trees. The most stable floor boards are those that have been quarter sawn but this is wasteful in production so we now use engineered wood flooring.

Dimensional Stability

This is what we call the movement of wood flooring. All wood will expand and contract and solid wood will move a lot more than engineered wood flooring. Movement is caused by the cell structure of the tree still being able to absorb moisture and expand and then in really dry or hot conditions (when central heating is on) to get rid of the moisture which means the flooring will then shrink. Installation of wood flooring will depend on whether it is engineered or solid and also what species it is.

Ends Matched

This means that the tongue and groove on the boards match each other and are also on the ends of the boards. This means that the end of a board can straddle a joist with the tongue and groove on the end matching each other and a full board either side giving additional strength.

Engineered Wood Flooring

This is the most stable wood flooring and is made up of good quality multilayer cross grain plywood back with a 4mm, 5mm or 6mm top layer. The thicker the top layer the more expensive the wood floor as more wood is used. These engineered boards should not be confused with the cheaper laminate either where there is a thin top layer like 1mm or 2mm and a softwood middle or the really awful cheap plastic imitation flooring.

Fair and Average Moisture Content F.A.M.C

Moisture content can be measured very accurately these days but it will always vary across a batch of wooden flooring due to the fact that each tree is individual just like we are and therefore the cellulose structure will vary which therefore follows on that moisture will vary. This is why we state that the moisture content will be 8% to 10% and is well within industry standard tolerances.

Wooden Fibre Saturation Point

This is the point (theoretically) when the cell cavities of a tree’s cell structure are totally empty of water but the cell wall still remains saturated. The moisture level of such wood is 20% to 30%

Wood Flooring “Figure”

The natural beauty of wood is brought out in wood flooring. There are many types of “Figure” as they are called such as the “birds eye” in Maple or medullary rays in Oak, you should always look at a manufacturers grading specification to see what you are likely to get when you purchase your wooden floor. Many displays only show the really good bits.

FSC Forestry Stewardship Council

This is a non-profit organisation responsible for controlling ethically and managed sources of timber. Full details can be seen on their site and as we are members with a chain of custody certificate you can see our own policy by clicking on the FSC link on the top of the page in the scrolling pictures.

Grading of Wood Flooring

There are various grades on timber, some manufacturers describe them as “Prime”, “Rustic” “Select” etc. There is no EN standard or BS standard for grading wood flooring so you need to understand what you are being sold. Prime may mean no knots or sapwood but it could mean very small knots depending on how the manufacturer defines their grading. So please check what the grading includes or excludes. For example Prime Oak may not contain any sapwood or knots or pin knots (pin knots are the size of a pencil point), but Prime Walnut may have some sapwood and knots as a characteristic of Walnut is its grain and knot variations. Click here to see our grading standards across our range of products.

Green Timber

This is a term used for unseasoned wood and is never used indoors only outside for structures where movement is not an issue.


Wood flooring is a hydroscopic material. This means that wood can attract water in and around its environment so that its moisture content increase when the air is humid and it will also lose this water when the air around it is hot and dry. Water will expand the wood and then when it dries out it will shrink, but either way it is never exactly the same, which is why poor quality wood flooring can warp and twist.

Honeycomb of Timber

This happens with case hardened timber where the outer zones of the wood set and harden without shrinking leaving the inner core to die. This type of timber is structurally weak and will not withstand the load bearing requirements for buildings.

Wood Knots

These occur as figures and sometime holes in the grain where once a branch grew out of the tree as it was maturing. In most cases these knots are very attractive and even where there is no actual knot the grain will swirl and vary due to the effect the branch had as it was being fed by the trees sapwood. Some tree have a lot of knots like walnut whereas others like birch have very few. We carefully grade our knots so that you know what you are getting (see grading above).

Laminate Flooring

This is a cheap plastic alternative and not only looks and feels cheap but is also a hydrocarbon product which means it is detrimental to our environment. It lacks warmth and resilience and we feel it is better to have a painted concrete floor than fit cheap laminate

Moisture Content

This is the amount of moisture in the wood flooring which for our manufactured boards is 8% this means that any subfloor that you fit our boards to must have a moisture content of less than 8% otherwise the hydroscopic tendencies of wood will draw the moisture up and the wood will swell which could have serious consequences for your flooring.

Moisture Meters

These are used to test the moisture content of your floor and subfloor. These measure wood moisture equivalent as the moisture content of wood will be fairly consistent in the same board due to its fibrous nature however sand/cement screed, plaster on walls etc will vary considerably according to their particular composition. Consequently they are measured with the same meter that is used to check your floor.

Parquet Flooring

There is a lot of confusion about this term, in reality it means small pieces of solid wood 8mm to 22mm thick in sizes 70mm x 250mm up to 90mm x 350mm which is used to make traditional herringbone or chevrons patterns. We have our EAZY FIT Parquet flooring blocks with sizes that will allow you to make up any pattern and long pieces you can use as a border.


This is a Pan European Forest Council whose task is like that of the FSC to ensure that all our flooring comes from sustainable sources and managed forests


These are where a lot of small pin knots form in a cluster it is similar to burrs on walnut and can be extremely attractive.

Plain Sawn

This is the common way to cut logs these days rather than quarter sawn. It means we get a lot more wood flooring from a tree and the log is sawn into slices across the tree.


This consists of thin layers of wood about 1.5mm to 2mm thick bonded together under high pressure. Most of our engineered wood flooring uses birch slices with the grain of each layer going the opposite direction of the other so that the board is totally stable.

Quarter Sawn

This is the old fashioned method of creating wood flooring. These boards are very stable as the tree is first cut into quarters (like a circle cut into 4 segments) and then each plank is cut from the quarter. Therefore these wood floor boards will not cup or warp like those that are plain sawn. Old galleons were made using this method and also Cathedrals and palaces and you can see the medullary rays (streaks) which are clearly visible running in swirls along the wood floor which looks fantastic.

Random Lengths

This is flooring where lengths can vary from 300mm to 1800mm on cheap flooring with an average length of 700mm. All our random length flooring starts with a 400mm long board and has an average length of more than 900mm

Random Widths

This means that someone has used different width boards when installing a floor to give a more random effect. In the old days boards were cut as they came from the trees and laid accordingly which is why in very old buildings you see lots of different width boards.


This occurs where sanding has not been done correctly.


This mainly occurs in Maple and is really attractive and makes Maple a floorboard to be prized.


This is the outer part of the tree that is very liquid and the cell structure is very open as it feeds the tree’s growth. It can bee seen as very light wood, on Walnut it looks white and in oak it is much lighter than the rest of the wood floor and is also softer as the cells have not matured.

Carbonising, Steaming and Thermo Treating

This is a variety of processes where the floorboard is heated to high temperatures which turns it darker and also at the same time making it stronger and less susceptible to moisture.

Stick Marks

For air or kiln drying, sticks are placed between the boards to allow air to circulate and sometimes these sticks can cause a mark in the wood normally when some form of chemical reaction takes place.

Sustainable Source

This means that the wood flooring comes from a sustainable source where the forests are managed properly and more trees are planted than are cut down.

Tongue and Groove

The groove is machined into the side of the wood floor board and the tongue is machined to exactly match the groove and protrudes from the edge of the board. The top of the tongue is normally 5mm to 6mm from the top surface or the floor board on a solid and engineered board, this means that you can sand a good quality engineered board as many times as a solid board. On good quality flooring the tolerance is important as if you want to float the floor you need as tight a fit as possible. In cheap flooring you will get very poor tolerances and therefore the boards will need to be filled with glue and the tongue and groove match will not give sufficient strength in the installation.


This is a defect in wood due to the cell structure shrinking excessively leaving a crack. These can open even more if the board shrink further after installation.


This happens when wood flooring dries out naturally or when it is being kiln dried, the moisture in the cell structure “fills” the cell like a balloon with air in it, when the wood is heated and dried the moisture disappears into the atmosphere. The moisture content of a tree recently cut down could be as much as 35% to 40% and when dried the timber will shrink more tangentially than radially. Shrinkage longitudinally is very minimal due to the cell structure of the tree.

Spalted Wood or Brown Oak

Spalting or browning of timber is caused by fungi growing on the tree during its lifetime. If there are black lines this would have been the fungi dissolving the wood in order to feed itself from the nutrients in the tree. It affects the colour, hardness and strength of the wood flooring if it has not been selected out.

Wear Layer

This is the solid top layer of Oak, Maple, Walnut or other species of wood that is glued to a base plywood board. Wear layers on our wood flooring are between 4mm to 6mm thickness and our unfinished sanded to 120 grit which means, if fitted properly you do not need to sand before applying oil.