Softwood Grades - Choosing the right grade for your job

Choosing the right grade of timber for your job is one of the most important things when embarking on a project. Most of the joinery timber imported to this country comes from Scandinavia, with some coming from Baltic countries. We’ll discuss both visual grades for decorative joinery projects and strength grades for timber used in construction projects. 

Visual Grades

The system used in Scandinavia now uses grades A, B, C and D, however for many years a system of Roman numerals was used I, II, III, IV, V, VI, VII (firsts, seconds, thirds, fourths, fifths, sixths and sevenths). Grade A now includes the old grades I-IV, grade B was V, grade C VII and grade D VII. Grade D is not exported for commercial use so we can forget that. The most important, and widely used, are A and B. The most commonly used grade being B or V (fifths) in the old system. Grade A, commonly referred to as ‘Unsorted’ includes a mixture of I-IV in the old system, and allows only very small knots in certain concentrations to meet this grade. This is the best commercially available grade of timber sold in the UK market. 

The name unsorted comes from the mechanical system that scans the timber as it’s produced and sorts the various lower grades as they pass on a conveyor belt, rejecting lengths with large knots or higher quantities of knots that are allowed in this grade. The timber that reaches the end of the conveyor and hasn’t been sorted into one of the lower grades is given the name unsorted.

Unsorted grade permits only very small, live knots, that aren’t barkringed or likely to come loose. There are limits on the number and position of knots and the direction of the grain. This grade is an excellent choice for high quality decorative mouldings, as dead, loose knots, will adversely affect the final finish when the mouldings are varnished or painted. 

Grade B (fifths) allows larger knots that can be dead, leaving a darker bark ring around them. They can be loose or have even fallen out. These knots can be higher in concentration, covering more of the piece than allowed in unsorted. This grade is perfectly serviceable for most joinery projects where a clear, knot free surface isn’t essential. Darker knots can be treated with knotting solution, to seal them, prior to painting so dark rings don’t penetrate the painted surface over time.

In addition to knots effecting the aesthetics of the timber they can also cause the timber to distort in a number of ways. Larger knots can interfere with the grain and create tension in the timber. When the timber is cut, the tension is released and can cause bowing, twisting and warping. The knot can also become a weak point in the timber with breakages often occurring at the site of a dead knot. 

Grade C (sixths) allows knots larger still and in higher concentrations in the piece. This grade can include other imperfections such as knot clusters, shakes (cracks in the surface of the piece), wane (bark still present from the outside of the tree giving an uneven edge to the piece), bark and sap pockets. This grade is used for low grade joinery where the timber is likely to be covered up with fabric, as in furniture manufacture, or in the packaging industry.

All of our decorative moulding such as skirting boards, architrave, picture and dado rails and smaller decorative panel mouldings are produced from unsorted Scandinavian softwood giving a nearly knot free product for the best joinery projects. Whilst it may cost a little more we believe the work needed to cut, use and finish is reduced by having a product with fewer defects and easier to paint, it’s a price worth paying.    

Strength Grades

The system used for strength grading is more simple than the visual grading rules. Most timber that is used in UK domestic and commercial construction is one of two grades, C16 or C24. The C simply stands for ‘Conifer’. There are one or two others but they are for very niche applications so we won’t cover them in this article. 

C16 grade is usually home grown, largely Scottish and Irish, and due to the climate in these countries the trees grow relatively quickly and this effects its density. This grade allows for a number of defects that may reduce the overall strength of the wood, such as knot size and location, grain deviations and wanes. There can be an unlimited amount of superficial defects that do not affect the strength of the wood, such as machine marks, surface chips and blue stain. C16 is the most widely used timber in the UK as it is strong enough to be used in most applications and is the most cost effective option.

C24 is imported from colder countries such as Sweden, Finland and Baltic countries, where the trees grow much slower giving a tighter grain and increased density. C24 has fewer defects than C16 graded timber giving a stronger, more stable timber. This grade usually has a more uniformed and neat appearance as there are fewer physical imperfections on the surface of the board. C24 is used where a higher degree of strength is required, often specified by architects where high loads or long unsupported spans are present. This higher quality is reflected in the price, which can be 15-20% more expensive than C16.

In addition to the strength grades chemical treatments can be applied to this type of timber to further enhance its durability. The most comment treatment process is pressure impregnation with Tanalith. In this process the Tanalith is forced into the timber under vacuum resulting in better penetration than simple surface applied treatment. The combination or C24 graded timber and pressure treatment gives our construction timber the best strength and protection, making it a great choice for almost any application.