EN 252:2014

Overview

EN 252:2014 - Field test method for determining the relative protective effectiveness of a wood preservative in ground contact (CEN) defines a standardized outdoor field procedure to evaluate how well wood preservatives protect timber when in direct soil contact (Use Class 4, EN 335). The method compares test preservative performance against a specified reference preservative using treated stakes partially buried in selected test sites and monitored for fungal decay, termite attack and combined damage.

Key topics and technical requirements

• Test principle: Treat wooden stakes to target preservative retentions, install partially buried stakes in the field, and periodically inspect and compare condition against untreated controls and reference-treated stakes.
• Test material: Sapwood of Scots Pine (Pinus sylvestris) is the standard; additional local hardwoods may be included. Wood must be straight-grained and defect-free.
• Stake dimensions & conditioning: Typical stake size (measured at ~12% moisture) is 500 × 50 × 25 mm. Stakes are conditioned to constant mass at (20 ± 2) °C and (65 ± 5) % RH before treatment.
• Number of stakes: Minimum 10 stakes per field for each preservative/retention; at least 10 untreated controls and at least two series of 10 reference stakes per field.
• Treatment process: Default full-cell (Bethell) process: initial vacuum < 10 kPa for ≥ 30 min, pressure ≥ 1 MPa for ≥ 90 min. Detailed records of each treatment charge are required.
• Retention measurement: Retention (kg/m3) is calculated from stake volume, mass uptake of treating solution and solution concentration. Stakes with individual retentions deviating > 10% from the series mean shall be rejected.
• Reference preservative: Composition and two target dry-salt retentions are specified (Cu/Cr/As mixture or alternative Cr-containing composition if As cannot be used). A fixation period (manufacturer’s recommendation) is required; for reference salts at least 3 weeks wrapped before air-drying.
• Assessment: Regular inspections record fungal decay severity, termite attack and combined damage. The method provides relative protective effectiveness compared to the reference.

Applications and users

EN 252:2014 is used by:

• Preservative manufacturers for performance validation and product development
• Independent test laboratories performing regulatory or certification testing
• Wood treatment plants to verify process efficacy and target retentions
• Specifiers, architects and asset owners assessing long-term durability of ground-contact timber
• Regulators and conformity assessment bodies for comparative performance data

Benefits include reproducible, field-based evidence of preservative performance under natural soil exposure and a standardized basis for comparison between products and retentions.

Related standards and notes

• Linked to EN 335 (Use Classes for wood in service) - ground contact = Use Class 4.
• EN 252:2014 supersedes EN 252:1989 and includes updated decay assessment criteria and informative annexes (site characterization, MoE testing, sample reports).
• Regulatory context: note restrictions on chromium- and arsenic-containing preservatives under EU biocide legislation (refer to applicable regulations).