BMW Technical Guideline - 019 Plywood Cladding - Government of Western Australia

BMW Technical Guideline
                               019 Plywood Cladding

1.1       Purpose
This guide sets out BMW’s requirements for specifying plywood cladding for government
building projects. This guide is required to be circulated to BMW consultants and contractors
when specifying and installing plywood cladding.

1.2       Background
Failure to correctly select or undertake proven procedures for selection, transport, storage and
preparation of plywood and the application of the applied finish coating may result in defects,
including surface cracking and fissuring of the plywood sheet and failure of the applied finish
can result in both aesthetic and structural failure.
These defects may not appear until after the contractual Defects Liability Period (DLP) has
ended. Remedial solutions may be protracted because solutions need to be monitored over a
reasonable period to ensure that rectification is adequate.

1.3       Recommendation
To manage the risks of using plywood particularly in external locations the Lead Consultant is
required to:
-     Provide clear and comprehensive Contract Specifications.
-     Ensure the Contractor conducts appropriate checks at relevant stages, including prior to
      departing factory, post-transport to site and prior to installation.
-     Ensure the Contractors Site Inspection records are comprehensive and up to date.
-     Verify at the initial check that the specified plywood is being used and specified sealant
      has been applied correctly to manufacturer’s recommendations.

1.4       Selection
The location of the project, regional requirements and local environments determine the
plywood selection for specific building projects. Specification of plywood grade suitable for
individual project is critical and take account of specific functional requirements.
Where a project is located in a region affected by cyclonic activity plywood may be used for
structural bracing and impact resistance of the building exterior. It is noted that these regions
are typically hot humid climate zones and therefore moisture resistance should be considered.

1.5       Types of Plywood
The following qualities of plywood sheeting should be considered for specific projects areas:
Face grading (veneer quality):
There are 5 face grade qualities specified for plywood in Australia - A, S, B, C, and D grades.

-   Grade A: high quality appearance grade veneer suitable for clear finishing
-   Grade S: an appearance grade veneer which permits natural characteristics –
    specification should clarify natural characteristics permitted
-   Grade B: an appearance grade veneer suitable for high quality paint finish – not suitable
    for clear finishing.
-   Grade C: Non-appearance grade with solid surface i.e. all open defects filled. Regarded
    as non-decorative appearance
-   Grade D: Non-appearance grade with permitted open defects i.e. limited number of knots/
    knot holes up to 75mm wide permitted. Typically used for structural application e.g.
    structural bracing.
Where plywood is used internally only, appearance Grade A, S or B plywood would be
appropriate to achieve the required standard of finish.
Stress Grade:
AS/ NZS 2269 refers to eight stress grades of structural plywood for use in structural
components and industrial applications. The higher the stress grade the thinner the plywood
required to perform the same structural function. Stress grades include F7, F8, F11, F14, F17,
F22, F27 and F34
Impact resistance:
In areas affected by high winds including cyclonic regions plywood is commonly used for
structural purposes for external walls including to provide bracing to wall framing and impact
resistance.
Fire Performance:
Fire resistance is the ability of a building component to resist a fully developed fire while still
performing its function. Plywood may be acceptable to meet fire resistant requirements but
must be used in combination with other non-combustible materials or chemical treatment/
coating.
Preservative Treatment (Termite):
Plywood is subject to decay and/or termite attack under certain conditions and correct
preservative treatment is essential for all plywood exposed to weather. Treatments may
consist of impregnation of veneers prior to manufacture, pressure treatment of manufactured
plywood or treating surfaces after manufacture.
Plywood with Type A bond used as an external cladding is required to be treated against
fungal and insect attack with a preservative treatment of minimum level H3 (outdoors above
ground) as defined by AS/NZS 1604.3
Bond/ Glue types:
Type A bond produced from phenol formaldehyde (PF) resin which forms a permanent bond
is typically suited to exterior plywood with long term full exposure or damp conditions. Type B
bond is formed from melamine fortified urea formaldehyde (MUF) and is typically used for
exterior plywood including concrete formwork.
Type C and D bonds are formed from urea formaldehyde resins (UF) and are typically used
for internal conditions. These bonds should not be used for any exterior use, exposure to
damp/ wet or long term bearing conditions.
Phenolic type A bonds have very low formaldehyde emissions (approx. E0) while urea
formaldehyde type bonds are below the 0.1ppm (approx. E1).

Marine Grade:
Marine Grade plywood is manufactured to AS/NZS 2272 Plywood – Marine. This plywood
consists of a Type A Phenolic bond and is manufactured for selected species based on
density, bending strength, impact resistance and surface finishing. This means that the marine
plywood has known and consistent structural properties and is typically stress grade F14.
Marine plywood typically has 2 x A grade face veneers.
Sealing / Coating:
Plywood used externally requires mandatory edge sealing is undertaken to minimise moisture
uptake through the panel end grain and to reduce risk of localised swelling and surface
checking at edges.
Sealing all sides of plywood sheeting prior to transport to site is considered good practice to
minimise damage from damp or wet conditions that may be inadvertently encountered prior to
installation on site and application of final seal coats.

1.6      Design/ Documentation Stages
At the design and documentation stages ensure the design/ detailing approach to the external
linings minimises exposure of any plywood cladding to UV and rain.
Where plywood is intended to be used as a structural element and specified to provide impact
resistance in cyclonic areas or structural bracing; clad plywood with an exterior lining to
provide mechanical protection. A prefinished/ low maintenance material would be suitable.
All exterior plywood is required to be Type A bonded and preservative treated to provide long
term durability. Where plywood is installed in a fully exposed location then additional
mechanical protection is required to be used e.g. prefinished metal or compressed fibre
cement or similar claddings.
Plywood that is not fully exposed to weather/sun (i.e. protected location) may have an A or B
grade face veneer and may have an approved quality paint or sealed finish. Particular care is
required in coating patches or plugs in plywood sheeting as they are more likely to move
independently and can cause paint failure.
Ensure the specification includes a provision for all plywood sheeting to be sealed with a sealer
approved by the Superintendent’s Representative, on all surfaces including sheet ends and
sides prior to leaving the factory.

1.7      Finish/ Coatings – Protected or Internal Locations
Paint systems such as oil based and alkyd enamel paint systems are not recommend for
external plywood. The EWPAA recommends the use of 100% acrylic latex paint system that
consists of 1 coat of 100% acrylic stain blocking primer and 2 coats of acrylic latex top coat.
An exterior, water repellent stain, compatible with specific preservative treatment, may be
considered for plywood in protected external and internal locations. Stained plywood exposed
to sun and weather will require on-going high levels of maintenance and is not considered an
acceptable finish.
The compatibility of any paint or sealing or staining system is required to be checked and
approved by the plywood supplier and the paint manufacturer. Any change of warranty
conditions is required to be confirmed in writing by the paint manufacturer and the plywood
supplier.

1.8      Construction Period
Risk of material failure is minimised if care is taken with the handling and storage of plywood
prior to installation. Prior to commencement of construction on site the Contractor should take
all reasonable steps to ensure plywood is in the best possible condition for its application.
Ensure that plywood sheeting is protected from the elements including condensation during
transportation, storage on site and post-installation prior to the application of final coating or
cladding.
Storage of plywood sheets in exposed conditions may result in damage to the plywood
including warping and swelling which will compromise the ability to install and finish plywood
sheeting to the required finish.
Storage should always be in a dry sheltered position with no solar exposure. Plywood sheeting
should be stored flat on rails, with top panel protected from changes in moisture. Ensure that
all flashings, trims, protective coatings and external linings are installed to the plywood
cladding as quickly as possible to minimise exposure to elements.
The Superintendent’s representative is required to inspect plywood sheeting to check that only
sheets that achieve the required finish quality are deployed for fixing.
Contractor shall ensure that fasteners/ fixings area compatible with the preservative salts that
may be present in fungal/ insect prevention treatment.

1.8      Maintenance
All plywood claddings are required to be inspected on a regular basis to ensure that
performance of the finish. During DLP this should be 2-3 times, then annually.

2        REFERENCES
Refer to the following documents:
NatSpec 0431 Cladding
NatSpec 0641 Applied Wall Finishes
NatSpec 0511 Lining
Australian/ New Zealand standards related to the Engineers Wood Products
Association of Australasia (EWPAA) products certification scheme:
AS/NZS 2269: 2008 Plywood – Structural
AS/NZS 2270: 2006 Plywood and Blockboard for Interior Use
AS/NZS 2271: 2004 Plywood and Blockboard for Exterior Use
AS/NZS 2272: 2006 Plywood - Marine
AS/NZS 4357: 2005 Structural Laminated Veneer Lumber
AS 6669: 2007 Plywood Formwork
Standards in relation to sampling and testing
AS/NZS 2097: 2006 Methods of Sampling Veneer and plywood
AS/NZS 2098: 2006 parts 1 to 8 Methods of Sampling Veneer and plywood
AS 2754.1 1985 Adhesives for Plywood Manufacturer

AS/NZS 2269.1: 2008 Structural Plywood – Determination of Structural Properties
Others standards that may be applicable to plywood:
AS 1684: 2006 Residential Timber frame Construction Code
AS 1720.1 1997 Timber Structures Code
AS 3610: 1995 Formwork for Concrete

3       DOCUMENT CONTROL

 TRIM Reference                                                                 02068651

 Date prepared                                                        14 December 2016

 Content Owner                  Assistant Director , Building Quality , Policy and Practice

 Version                                                                               1.0

 Next revision                                                        14 December 2018

 Enquiries          Consult with Content Owner or principal.architect@finance.wa.gov.au

4       DOCUMENT APPROVAL
This guideline was endorsed and approved for use on 14 December 2016 by:

Carolyn Marshall, Principal Architect
Building Management and Works