Palm plywood – wood or not?19 December 2009 by Dr Vic Kearley
Dr Vic Kearley, section leader, Engineering and Product Services, gives TRADA’s view on the thorny issue of palm-cored plywood
• Palms’ structure and form differ from those of hardwoods.
• TRADA says palm ply can be tested and marked in accordance with BS EN13986: 2004
• It says it should be described with the “palm” prefix.
• A much greater degree of testing is needed than for conventional plywood.
The issue over whether palm plywood can be referred to simply as plywood, with no further qualification, has been hotly debated in the timber trade for a while. This is understandable as it’s a complex question.
Chemically, palm stems are made of lignocellulosic material, like wood. But botanically, they are members of the ‘woody’ Monocotyledons order of angiosperms, which also includes bamboo. Hardwoods are also angiosperms, but come from the Dicotyledons order.
Hence there is a botanical difference between the classification of conventional hardwoods and the palms. A palm’s microscopic structure is also different from hardwoods, with significant variation in structure and density along and across the stem. Palms lack the ‘lateral meristems’ present in hardwoods, that allow for ‘secondary thickening’, despite their tree-like appearance. So, despite being a member of the angiosperms, their structure and form differ from hardwoods.
In common parlance, trading and use terms, however, the situation regarding palms is less clear-cut. A growing palm is commonly referred to as a tree, even if its microscopic structure is different from a hardwood, with BS 6100-1: 2004 Building and civil engineering – Vocabulary - Part 1: General terms defining wood as “lignocellulosic substance between the pith and bark of a tree or shrub”. Most people would accept that palm material meets that definition, despite the botanical differences between palm and softwood/hardwood.
The outward appearance of palm material is also similar to wood and, as a result, has been reportedly viewed by HM Revenue & Customs as wood “by association”. There are also many palm products that have been traded internationally as palm wood for many years in established markets. And in Trading Standards terms, there are precedents for products being described in terms of common English usage rather than scientifically accurate terms and this appears to be applicable to palm wood products. The timber industry sells its products primarily to other members of the timber trade, to the wood-using industries and to the public, most of whom could not be expected to have an in-depth knowledge of the botanical structure of the products they are buying.
Whatever the market description of the material, whether palm plywood if made from palm veneers or, palm core or composite plywood for products with palm core and other wood external veneer, it must comply with the requirements for these definitions as given in BS EN313-2: 2000 Plywood. Classification and terminology. Part 2: Terminology. This is the guidance given in a recent statement by BSI Committee B/541 and further circulated by The Timber Trade Federation’s National Panel Products Division. Further complicating the matter, however, this statement was based on the assumption that palm cannot be considered as a wood and further investigation since the B/541 meeting has cast doubt on this assumption.
Considering all the above, TRADA has concluded that such palm veneer products could correctly be described as palm plywood and sold on that basis. As such they can be tested and marked in accordance with BS EN 13986: 2004 Wood-based panels for use in construction. Characteristics, evaluation of conformity and marking and BS EN 636: 2003 Plywood – Specifications. To avoid misunderstandings it should probably not be described without the “palm” prefix as that could be considered misleading.
If a palm product is to be used in non-construction applications, such as furniture, suppliers need to demonstrate that it is fit for purpose, and this can simply be agreed between supplier and the purchaser.
If it is for construction use then, as with all plywood, the supplier must demonstrate compliance with the European Construction Products Directive (CPD). For products qualifying as “plywood”, the most straightforward route for this is by demonstrating compliance with the CE marking requirements of BS EN 13986. However, in the case of panels containing palm-based materials, the assumptions which allow Classification Without Further Testing (CWFT), for properties such as reaction to fire, should not be made without supporting test evidence.
It is clear that a much greater degree of testing will be required for these materials than for conventional plywood. The extent of this will depend on end use and whether the panel is intended for structural or non-structural use, but might include tests for durability, reaction to fire, mechanical properties and stability. It’s back to that well-worn phrase, caveat emptor. Know what you are buying and ask for evidence that it does what it says.
For further information contact Vic Kearley at firstname.lastname@example.org or on 01494 569600.