So you want to know about timber grades…
Grades are the timber industry’s way of telling whether a piece of timber is good for the job. Whether it’s strong enough, what mix of grain & knots it has, what sort of colouring it has, all sorts of things.
As with all traditional craft or artisanship, the transfer of wisdom and knowledge that only grows out of experience and gets passed down over time is insufficient for 21st century application. The timber industry is a prime example of this.
So before we get into the explanations of grades using Oak as an example, it’s worth noting that although every piece of wood is unique – reflecting the species of tree, it’s growing history, the climate, geology, geography, level of management and all the other things that can act on a tree to give it’s wood the appearance and characteristics it does – these well understood variables have now been studied and specific scientific timber grades have been established and documented to make visual identification of grades universal, usable by manufacturing, engineering, architecture and other industries.
One significant reference to aid timber grading and therefore specification is the publication Making the Grade. Well worth a read if you want to build your wood knowledge and understanding and a must have if you use timber in your work.
Download a copy by clicking on the book below and see MORE useful links at the bottom of the page.
For simplicity’s sake we talk about most of our stock, especially our furniture making and joinery Oak, in terms of Character, Prime or Super Prime…
Technically, as documented by Making the Grade, this refers to a relatively low grade of timber that exhibits a mix of inter-grown knots, pin knots, heart shake, or colour variations.
At English Woodlands Timber we use the term Character Oak to describe a very broad grade that includes anything that falls below Prime, 1st grade Oak standards with exceptions only for our feature grades
This then means under the term Character our boards include 2nd Grade Oak and incorporated sub grades plus may include pin knots, splits, cracks, heart shake, insect attack, bark pockets, areas of rot, sapwood and colour variation.
As an overview we don’t put restrictions on boards in this grade providing the appearance and mechanical properties of the particular timber are suitable for its intended purpose.
Our actual stock then incorporates particular selections within the grade of Character Oak.
Waney Edge Character Oak stock will generally sit in original boules and we select and measure from the stack depending on each customers requirements, preferences and the particular use for the board.
Square Edge Character Oak stock is a different thing altogether.Here a more sophisticated, applied grade selection has been carried out and boards are stocked in packs of similar grade qualities.
These packs tend to contain the higher qualities of Character Oak, the 2nd grades which exclude more rustic features and in terms of appearance are more representative of real Oak with good grain patterns, sound knots, lovely honey colouring… everything one normally expects from real Oak.
This means by selecting from packs it’s possible to get a consistent grade and overall ‘look’. This speeds up selection and is useful for flooring projects, cladding projects, bespoke kitchens, door manufacture, furniture range manufacture etc where all boards need to have similar colouring, knot sizing and grain pattern. By selecting from graded packs of Square Edge Oak you get a reassuring consistency, even in Character grades.
WATCH our Guide to Character Oak video
The term Prime has always been used to indicate the top grade of timber.
It’s criteria is used to verify the mechanical properties of a board by visual means and seeks to differentiate Prime graded boards as boards that are fit for specific purpose, namely joinery, cladding, cabinetry, furniture making or highly machined timber products.
In this way, the grading of Prime timber is about what is allowed within a board outside of straight grain, even colouring and good quality wood husbandry.
In Prime Oak we allow one inter-grown knot* up to 20mm diameter or several small knots up to a 20mm combined diameter**. One small bark pocket is allowed. Small sap bands are allowed.
In selecting from Prime Waney Edge Oak boards to a cutting list or customer requirement we would measure out the waney edges (re:sap), the heart cracks, large knots, shakes and other typical board features that are not allowed within the grade so the board measure (the bit you pay for) would only include what comes within Prime grade, although you may receive a whole waney edge board.
In this way Prime timber does waste more wood than other timber grades but it is how a single, unique waney edge board can be used to select for a multitude of grades and purposes and is one reason we love our waney edge timber.
Our Square Edge Prime Oak timber has been pre-selected into grades at the milling stage and is an easy, reliable, fast way to buy Prime Oak, especially if you are self-selecting. These boards can be just taken straight from a timber stack and each board measure meets the stated grade on at least one face, if not both.
For homegrown waney edge Oak take a look at Making the Grade – Oak grade 1 for illustrations of Prime Oak
WATCH our Guide to Prime Oak video
SUPER PRIME OAK
Super Prime is a term that indicates a grade ‘above’ Prime.
In truth, technically Super Prime hasn’t been documented or normalised as a timber grade in the UK and isn’t a scientifically recognised term. It’s a description we use of a grade that goes above and beyond normal Prime Oak timber qualities and requirements.
Super Prime is a selection of the most pristine, the most clear, the most pale and evenly honey coloured, usually Eastern European, Prime Oak you will ever see. I think we’ve called it ‘relentlessly clean’ before and that about sums it up.
Knots aren’t strictly excluded but if you see one it’ll be small and only visible on one face. The other face will undoubtedly be clear. In Super Prime Oak there will not be a lot of grain pattern. There will not be a lot of variation of anything. There will be no dark colouring. No bark pockets. No wild grain. No splits, no cracks, no shakes. There may be a high proportion of Quarter Sawn boards. There may be a lot of very flat boards. There may be a lot of very straight boards.
If you have a large run of Oak doors and you need them all to look and behave the same, use Super Prime. If you need a quiet, understated solid wood for an interior surface use Super Prime. If you need simple elegance with embodied strength and durability for a feature staircase use Super Prime.
Although it’s a little hard for us to admit, Super Prime Oak has superior qualities that cannot be replicated by other grades or timber species. For this we are grateful as it is a pleasure to work with, a pleasure to select from and a thrill to see it in situ in a customer project.
WATCH our Bitesize Guide to Prime Oak video
FEATURE OAK GRADES
These are not all strictly grades of oak, although some are (Making the Grade will guide you) but include certain desirable qualities produced by the tree.
This is a very popular feature in Oak resulting from the presence of frequent small pin knots. The can appear singly, in 2’s or 3’s (cats paw) or in groups of growing density which we describe as light, medium or heavy pip depending on number of knots in a group.
TIGER or BROWN OAK
This describes an attractive colouration caused by the beef steak fungus Fistulina hepatica. We see it in Oak and it produces two different effects.
The first is a narrow brown streak going down through the grain that can hit and miss to produce a variable stripe. This is the Tiger Oak, surprise surprise! Super jazzy, it’s a wonderful vibrant alternative to an exotic species therefore prized by sustainable minded, conscientious designers and makers.
The Brown Oak is where the whole whole cross section of the heartwood is affected, leaving a solid brown colouring known, funnily enough as Brown oak. This may not sound too special but the colouring is so deep and chocolatey and different to anything else that it’s a joy to see and an absolute gift to cabinetmaker looking for that something special.
Burr describes what appears to be dense area of pin knots covering more than 50% of a board. It’s a spectacular visual effect, much sought after and is actually a feature caused by irregular grain growth around groups of epicormic buds.
Although Burring does change the mechanical properties of a board by interfering in the growth of the grain as the knots are so tiny and woven into the grain the board stays intact. Burr boards take more care to dry. They retain moisture differently to a straight grain board. They dry differentially in thickness and hold onto moisture in little pockets. This can produce undulations in the sawn surface but they can be worked very successfully for furniture making, box making, cabinetry etc
We have normal Burr boards but we also keep the actual burrs (big lumpy things) taken from the outer log prior to sawing. These are for special projects, wood turning, one off furniture pieces and the like. If you’re a Burr fan you’ll love these pieces.
QUARTER SAWN OAK
This is the term for boards sawn on the radial plane to reveal the very decorative figuring known as medullary ray. A visible medullary ray (shiny flame pattern) and vertical growth rings in the end grain indicate quarter sawn timber.
This vertical grain means that boards will have maximum potential for stability. This is due to an absence or relative absence of curve/growth ring in the thickness therefore the absence of tension and/or compression inherent in the growth rings that act on boards to cause cupping.
We choose not to saw entire logs by the quarter sawn method but instead our T&T*** sawmilling produces a number of quarter sawn boards near the centre of every log which allows us to select for quarter sawn boards but also select for varying strengths of fabulous grain pattern that occurs in outer and crown boards.
The best of both worlds!
*inter-grown knot, alternatively know as sound knot = a knot that the grain has grown through/into rather than around/against so that it is integral in the body of the timber. An unsound knot has grown separately to the flow of grain and can move separately, can be dislodged or even fall out.
**E.g. 1 knot at 6mm diameter + 1 knot at 5mm diameter + 1 knot at 7 mm diameter = a total 18mm diameter and therefore is allowed within Prime grade
***T&T Through & through sawing produces the same boards as plain sawn or also rift sawn