Six Birch Plywood Grades, All Birch Core

A plywood grade tells you what the two face veneers look like. It does not tell you how strong the sheet is.

CP is a repaired grade, not a weak one. The mill fills every defect that could affect strength, so a CP sheet carries what a BB sheet carries. Species, veneer thickness, ply count and adhesive are identical across our sanded grades. Paying up to BB buys appearance.

What you are choosing between

Six grades, all from the Stiga RM mill in Kuldiga, all 100% birch veneer: 1.5 mm plies laid cross grain, phenol formaldehyde (WBP) glue, density around 680 kg/m3, moisture content 10% plus or minus 2%. No poplar core, no birch faces over something cheaper. Check the cut edge and you will see uniform birch plies.

We publish the thickness tolerance for every listed thickness, which most importers do not. Grade has no bearing on it: a nominal 18 mm sheet is permitted anywhere from 17.1 to 18.7 mm whatever the letters say. The thickness guide has the rest.

And you mix grades and thicknesses in one load. BB/BB for the doors, CP/CP for the carcasses behind them, two packs of F/F on the same truck, confirmed at quotation.

What the grade is grading

Every sanded grade is made to EN 636-2S, bonding class 2 under EN 314, interior and humid. C/C and BB/BB carry the same classification. Same mill, same core, same glue. Grading happens at the veneer sorting line and at the sander, and all it changes is two faces, graded apart. First letter the face, second the back: BB/CP is a BB face over a CP back.

What each grade permits

These are the mill's published limits, as the mill states them.

C grade permits all sound and unsound knots, open knots and holes up to 40 mm with up to 10 per m2, open splits up to 10 mm wide, discolouration and dents, and up to 50% of the surface left unsanded. Delamination and bark are never permitted at any grade. Open holes and half the face unsanded makes C/C a utility face, not a cosmetic one.

CP grade, also written grade IV, permits sound knots up to 40 mm, repaired knots and holes up to 15 mm, repaired open splits up to 600 mm, discolouration and curly grain, and up to 5% unsanded. The word doing the work is repaired. A 40 mm hole in a C face stays a hole. In a CP/CP face it is filled.

BB grade, also written grade III, permits sound intergrown knots up to 25 mm, small repaired knots and holes up to 6 mm filled with matched wood inserts and up to 10 per m2, and light discolouration on up to 15% of the surface. No open defects. Both faces sanded. Three numbers separate BB/BB from CP: knots 25 mm against 40 mm, repairs 6 mm against 15 mm, matched wood inserts rather than filler. A BB face still has knots and repairs. It is a clean commercial face, not a flawless one.

F1 film, standard on F/F and F/W, permits minor film stains on up to 15% of the surface and small matte areas, with no delamination. F2 is available for rough work on request.

We publish no limit on colour variation between sheets, and no face veneer thickness distinct from the 1.5 mm core plies. Ask us at quotation if your job turns on either.

Letters mean nothing without limits

Grade letters carry no enforceable standard across the industry. Mills and merchants use B, S, BB, CP, C and the Roman numerals I to IV for quality bands that overlap, so a BB from one supplier is not a BB from another and a grade IV from one mill is not the CP above. We publish the maximum sound knot size, the maximum repair size and the unsanded percentage for every grade we sell, in writing, with the quotation. Ask whoever else is quoting you for theirs. If the answer comes back as the letter again, there is nothing to compare.

The four way comparison

	C/C	CP/CP	BB/CP	BB/BB
Face appearance	utility. Open knots and holes to 40 mm, open splits to 10 mm, dents, discolouration	sound knots to 40 mm, repairs to 15 mm, repaired splits to 600 mm, curly grain	clean. Sound knots to 25 mm, matched inserts to 6 mm, no open defects	clean. Sound knots to 25 mm, matched inserts to 6 mm, no open defects
Back appearance	same as face	same as face	CP. Repairs to 15 mm, repaired splits permitted	same as face
Sanding	up to 50% unsanded	sanded, up to 5% unsanded	both faces sanded	both faces sanded
Use it for	hidden structure, packing, crating, sacrificial layers, substrates that get covered	structural and concealed work, lamination substrates, floors under a finish, jigs	carcasses, cabinet backs, shelving, linings where one side shows	doors, exposed shelving, furniture, ceiling and wall linings
Visible surface?	no	only where a workshop finish is acceptable	face yes, back no	yes, both sides

CP/CP and BB/CP are the same sheet on the back. Specify BB/CP for a carcass that goes against a wall and you pay for the one face you see, which is right. Hide both faces and CP/CP is the call.

C/C is not a cheaper CP/CP. The 50% unsanded allowance and the open holes rule it out as a lamination substrate: a 40 mm hole telegraphs through a thin face material and an unsanded surface will not bond even. For laminating, CP is the floor.

The spread from our cheapest sanded grade to our dearest is about 15%, which the price guide sets out. Dropping a grade saves a fraction. Push the borderline decisions upward.

F/F and F/W

A different proposition, not another step up the same ladder. F/F is smooth phenolic film, dark brown, both sides. F/W adds a wire mesh anti slip film on the face. Both are made to EN 636-3S, exterior and humid, rather than the 2S on the sanded grades, which is why these two and not BB/BB are the answer for formwork, trailer floors, ramps and anything that meets weather.

The edges come sealed with water resistant paint. Film protects the faces, paint protects the exposed end grain, and together they set the service life. Cut one on site and you have opened an edge that needs resealing.

Film weight is 120 g/m2 as standard, 220 g/m2 on request for more reuses. Counting pours, ask for the heavier film. Reuses per film weight are not published, so take no number from anyone who quotes you one. Film thickness runs 6.5 to 35 mm on request, against 6.5 to 40 mm uncoated.

Choosing

Water or weather takes F/W where the surface must be non slip and F/F otherwise. Everything else, count the faces that will be seen. Two, BB/BB. One, BB/CP. None, but structural, laminated or needing a sound sanded surface, CP/CP. Nothing visible and nothing bonded, C/C. Anything bonded or finished counts as visible, because laminate, veneer, paint and lacquer all reveal what is underneath. The applications guide works through this by job type.

Tell us the load

Grade, thickness, square metres, destination. You get a pack count, a price and the certificates. Minimum is half a truck, about 8 packs, roughly 18 m3 or 12.5 tonnes, and mixing grades across it costs nothing extra.

Request a quote or browse the full range.

The mill produces to order and holds no stock, with production up to 3 weeks depending on season plus transit, so a job starting next week is a merchant's job and we will say so.

Related reading

• Birch plywood direct from the mill
• How birch plywood is priced: per sheet, per m2 and per m3
• Plywood thickness guide, including the tolerances
• How much plywood fits on a pallet, a truck and a container
• Plywood for furniture, construction and interiors
• Birch plywood compared: softwood, poplar and Finnish birch