Plywood and OSB in Construction
Plywood
Plywood is a wood based panel product consisting of layers of veneers glued together, with the direction of the grain in adjacent layers at right angles. It is available in various species and qualities dependent upon the end use.
MDF
MDF is a wood based sheet material manufactured from wood fibres bonded together with a synthetic resin adhesive and suitable for a wide variety of interior uses. For more demanding situations MDF is also available in moisture resistant, flame retardant, high density and exterior grades.
OSB
OSB is an engineered wood product formed by layering strands of wood in specific orientations. It is compressed and bonded together using both wax and resin adhesives. There are two main types, OSB 2 for use in dry conditions and OSB for structural use in humid conditions.
Particle Board or Chipboard
Particle Board is an engineered wood product manufactured from wood chips, shavings and/or sawdust then pressed and bonded together with a synthetic resin. This product is mainly used as a carcassing material in the furniture trade or as a flooring product.
Marine Plywood to BS1088: 2003
Marine Plywood should meet the requirements of BS 1088:2003 (Marine Plywood). BS 1088 comes in two parts, Part 1 (Requirements) and Part 2 (Determination of Bonding Quality Using Knife Test). The key requirements from part 1 of BS 1088 are highlighted below. However, this is no substitute for purchasing and using the full version of the standard. Requirements of manufacture include classification according to panel type, Standard (S) and Lightweight (LW). Standard marine plywood has veneers possessing outstanding durability with respect to fungal decay and bonding quality making it suitable for marine construction while lightweight marine plywood is of veneers from timber species of lower density/ durability than those in standard marine plywood while all other requirements remain the same.
Veneer Durability
Standard marine plywood as defined in BS 1088 should have outstanding resistance to biodeterioration (durability) with time. The biological durability of marine plywood is expected to be greater than that of plywood of the same species that meets the requirements of BS EN 636-3. In this respect, Standard marine plywood should be made throughout of timbers having a durability rating of class 3, BS EN 350-2, or better and a nominal density of > 500kg/m3 and up to 5% sapwood per veneer is permitted.
Number and thickness of plies
According to BS 1088, Marine Plywood panels having a thickness of 6.5mm or less should have three or more plies. Panels having a thickness of greater than 6.5mm should have five or more plies. With 3-ply panels, the combined thickness of the two outer plies after sanding should be between 40% and 65% of the nominal unsanded thickness of the panel. With 5-ply panels, the combined thickness of the two outer plies after sanding, combined with those of the core and other inner plies with their grain direction parallel to the outer plies, should be between 40% and 65% of the nominal unsanded thickness of the panel. Additionally, for panels with nominal thicknesses of greater than 3.8mm, each outer ply should not be less than 1mm thick after sanding and each inner and core ply should not be more than 4.8mm thick.
Manufacturing Defects
In accordance with BS 1088, all marine panels should not contain any of the following manufacturing defects: open joints (e.g. core gaps, overlaps and pleats, blisters, hollows, bumps and imprints), roughness (other than that due to the irregular structure of the wood), sanding through, foreign particles, defects in the edges of panels (e.g. due to sanding, sawing, missing wood).
Bonding Quality
All marine plywood as defined in BS 1088 should have outstanding resistance to loss of bond strength with time. When tested in accordance with BS EN 314-1, the bonding quality should meet a minimum requirement of BS EN 314-2, Bonding Class 3.
Marking
Panels conforming to BS 1088 should be indelibly marked on the back or edge with the following information in the order shown:
1) The number and date of the British Standard “BS 1088-1:2003” and the word “MARINE”
2) The word “UNBALANCED” if panels are of unbalanced construction
3) The word “TREATED” if there has been any application of preservative treatment
4) The nominal panel thickness
5) The manufacturer’s name or ID mark
6) The country of manufacture
7) The panel type (Standard (S) or Lightweight (LW))
8) The name of the timber species according to BS EN 350-2:1994 In addition, the documentation for each consignment of panels should include the marking information above and a list of all the species used in their construction and details of any preservative treatment which has been applied.
