2. BS EN 314 - Plywood - Bond quality

Part 1 : 1993 Test Methods

This specifies methods for determining the bond quality of veneer plywood by shear testing. The principle of this method is technically equivalent to appendix A of BS 6566 : Part 8 1985 - Specification for bond performance of veneer plywood.

Before carrying out the shear tests, the plywood samples are required to undergo a sequence of pre-treatments e.g. Section 5.1.4 calls for immersion for 72 (± 1) hours in boiling water followed by cooling in water at 20 (± 3)°C for at least 1 hour to decrease the temperature of the test pieces to 20°C.

Part 2 : 1993 (re-confirmed 2001) Requirements

Specifies requirements for bonding classes of veneer plywood according to their end uses.

(This supersedes clauses 1, 2 and 3 of BS 6566 : Part 8 : 1985. It was clause 2 Table 1 that listed WBP as a bond type and named US Product Standard PS1 as an acceptable bond quality equivalent to WBP).

Three classes of bond quality are listed:

Class 1 Dry Conditions

interior applications with no risk of wetting (12% or less moisture content – 20°C 65% relative humidity).

protected exterior conditions (20% or less moisture content – 20°C at 85% relative humidity).

Class 3 Exterior

unprotected exterior conditions (above 20% moisture content).

These three bonding classes relate to the hazard classes laid down in BS EN 335 - Hazard classes of wood and wood-based products against biological attack - Part 3 : Application to wood based panels (see Table 1).

BS EN 314-2 Section 4 Table 1 gives the relationship between the respective bond classes and the pre-treatment conditions. For bond class 2 (protected exterior conditions) there are two pre-treatment conditions the plywood test pieces must undergo before shear testing can commence. Similarly, for bond class 3 (unprotected exterior conditions) there are three pre-treatment conditions - see Table 2.

Table 2

APA Plywood and bonding classification

* Exposure 1 panels are manufactured with the same phenolic adhesives used for Exterior panels, but due to other compositional factors, Exposure 1 panels should only be used in applications where their ability to resist moisture and weather during long construction delays is required prior to providing protection.

APA Exterior plywood complies with the requirements for European bond class 3 as laid down in BS EN 636: Plywood - Specifications Section 3.3 - plywood for use in exterior conditions.

APA Exposure 1 plywood complies with the requirements for European bond class 2 as laid down in BS EN 636: Plywood - Specifications Section 3.2 - plywood for use in humid conditions.

Both APA Exterior and Exposure 1 bond durability classifications are eligible for use under Eurocode 5 section 3.4.1.1 (p) 2 and (p) 3 respectively.