Radiata Pine, Marine Ply : About Plywood

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ABOUT PLYWOOD			PRINTER VERSION
Some useful tips and Info Plywood Grades ‘A’ Grade An ‘A’ face on ply means it has a high quality clean face basically clears grade suitable for clear/stain finishing. ‘B’ Grade A ‘B’ face will have a permitted quantity of small knots, high quality suitable for a paint, whitewash or stain finish. ‘C’ Grade This grade will likely have knots and splits with filler and sanded, medium grade. ‘D’ Grade This will likely have open knots and splits and may be unsanded, rough appearance. There are also some low grade plywoods that come available from time to time but are rated non-structural and priced accordingly. Some examples of the above grades would be; AA Grade 2 ‘A’ faces, good both sides AB Grade one ‘A’ face with a ‘B’ back AD Grade one ‘A’ face with a ‘D’ back BB Grade 2 ‘B’ faces CD Grade one ‘C’ face with a ‘D’ back DD Grade 2 ‘D’ faces, rough both sides Radiata Plywood general info Radiata ply available in New Zealand is bonded with a water proof glue (type A or WBD phenolic) easily identified by its dark colour. The sheet sizes are generally 2400 x 1200 although some are available in 2440 x 1220 and 2700 x 1200 A selection of radiata is available in a tongue and groove format ideal for applications such as decking, roofing, flooring, ceilings and wall panels. Plywood must be used where a under floor heating system is used as opposed to particle board which has the problem of formaldehyde emissions. The veneers are rotary peeled even layers pressed to achieve a standard thickness, the number of veneers varies from mill to mill but a guide would be;
3 ply 5ply 7ply 9ply 11ply	4mm, 7mm, 9mm 12mm, 15mm 17mm, 19mm, 21mm 25mm 33mm
Treatments Radiata plywood is available in 3 finishes;
Untreated CCA Treated LOSP H3	No preservative at all, mainly interior, OK outside if painted. (Copper, Chrome & Arsenic) H3 Treatment, green colouring on sheets. Do not use with aluminium boats or near aluminium (causes electrolysis). Ideal for under butyl membranes, suitable for marine glues and resins, all exterior uses. (Light Organic Solvent Preservative) H3 Treatment, clear finish, ideal for staining, all exterior uses. Not suitable for under Butyl membranes and is not compatible with marine glues and resins. Is an above ground treatment only, for on or in ground use H4.
Cladding It is recommended that Stainless screws be used for outside applications. Any H3 treated plywood is suitable for exterior cladding although there are some specialty products available for this. These would be LOSP treated having a ‘Bandsawn’ finish with either a grooved or non-grooved appearance. They also have a shiplap type of edging which has a weather seal and allows for expansion (3mm recommended). These sheets are generally 12mm thick which is the standard for cladding although 9mm would be the thinnest recommended. Bracing Structural plywood is the ideal plywood used for bracing in walls, roofing and sub floors. The beauty of plywood opposed to other products is that as well as forming a bracing effect it may also be your finished surface making a cost effective solution. Marine Plywoods & Marine Bonded Exterior Plywoods Marine plywoods are made up from many species of timbers selected for their individual qualities. These may be hardwoods selected for their strength or timbers selected for lightness, their bending ability, surface finish, strength etc. These plywoods are commonly used in the construction of marine craft and motorhomes where strength and weight are important factors. These also have a type A phenolic glue which meets with international standards. Usual sheet size would be 2440 x 1220 with some Gaboon being 2500 x 1220 and also 3050 x 1530 and 3100 x 1530. Common grades would be;
BS1088 Marine Grade BB BB/CC		A high strength marine ply with 2 very good faces and zero core gaps. The top spec for common marine Plywoods. 2 ‘B’ faces as described above, a few small core gaps, small filled splits on faces acceptable ‘BB’ face with ‘CC’ back, core gaps acceptable, BB faces may have small filled & sanded defects. ‘CC’ back may have rough patches & filled splits
(BB & BB/CC are marine bonded exterior grades) Architectural Plywoods These are plywoods commonly used for cabinetmaking and would include the Marine Plywood range with some of the top grade Radiata’s as well as some specialist plywoods. Some of these would include species such as Hoop Pine, Birch, Fiji Kauri and Brown Wood (Keruing) being the common ones. We also offer the facility to press a wood veneer onto a sheet of marine ply (usually Meranti) for that extra special finish. See elsewhere on our web site for a comprehensive list of species available.