Specification for preservative-treated plywood
1969 Edition

IS 5539 outlines four preservative categories for plywood protection:

• Type 1 (Oil-Based): Includes coal tar creosote and petroleum oils with high boiling points.
• Type 2 (Organic Solvent-Based): Comprises chemicals like copper naphthenate, zinc naphthenate, pentachlorophenol, benzene hexachloride, and DDT.
• Type 3 (Water-Soluble Non-Fixing): Contains zinc chloride, boric acid, borax, sodium fluoride, and sodium pentachlorophenate.
• Type 4 (Water-Soluble Fixed): Encompasses copper-chrome-arsenic compounds, acid-copper-chrome, chromated zinc chloride, and copper-chrome-boric mixtures.

For detailed descriptions, refer to IS 401-1967. The standard also emphasizes the impact of preservatives on adhesive bond strength and surface treatments.

IS 5539 prescribes that preservative application on plywood should be carried out using brushing, spraying, or brief dipping methods. At least two coats are required, with the second coat applied when the first is partially dry but the surface remains damp. Edges must receive thorough treatment to ensure complete protection. Any cutting or drilling should be performed prior to preservative application; if done afterward, exposed areas must be promptly brush-treated. The treatment uses one of four preservative types (oil-based, organic solvent-based, water-soluble non-fixing, or water-soluble fixed) to achieve surface protection with limited penetration.

IS 5539 specifies preservative retention values based on the service environment and preservative type:

• Water or ground contact with painting (e.g., pontoons): Type 4 (Copper-Chrome-Arsenic or Acid Copper-Chrome) with 12.0 kg/m³ retention via pressure or veneer treatment.
• Same conditions but with light or no painting: Type 4 at 12.0 or Type 1 (Creosote or Creosote-fuel oil 50:50) at 10.0 kg/m³ via pressure treatment.
• Marine structures exposed to borers: Type 1 with 20.0 kg/m³ retention using pressure process.
• Concrete shuttering plywood: Type 4 at 12.0 kg/m³ via pressure or veneer treatment.
• Exterior cladding or roofing with paint: Type 4 at 12.0 kg/m³ via veneer treatment.
• Exterior exposed without concern for paint color: Type 1 at 10.0 kg/m³ via pressure.
• Bus or rail flooring: Type 4 or Type 1 at 7.5 kg/m³ via pressure.
• Interior applications not exposed to ground moisture: Type 4 or Type 2 at 4.5 to 5.5 kg/m³ via pressure or soaking.
• Decorative interior paneling: Type 2 or 3 at 4.0 kg/m³ via pressure or soaking.

These values ensure durability against decay, insect attack, and environmental factors.

IS 5539 mandates preservative treatment for all sapwood and the heartwood of non-durable species. Durable heartwood requires treatment only when utilized in harsh environments such as ground contact, marine exposure, or termite-prone areas. Species are categorized by durability classes (I - highly durable, II - moderately durable, III - less durable) and treatability ratings (a to e, where 'a' is easiest to treat). Examples include:

• Tectona grandis (Durability Class I, Treatability c)
• Dalbergia latifolia (Class I, Treatability e)
• Mangifera indica (Class III, Treatability a)
• Acrocarpus fraxinifolius (Class III, Treatability c)
• Terminalia tomentosa (Class II, Treatability b)

Thus, treatment is compulsory for sapwood universally and for heartwood depending on durability and use conditions.

IS 5539 ensures treatment quality by prescribing standardized application methods including soaking and surface treatments, with clear procedural clauses (5.2.2). It mandates penetration testing through sampling at minimum distances from edges, employing IS 401:1967 Appendix C methods like boring and chemical analysis to verify preservative depth. Minimum absorption levels are defined to guarantee sufficient uptake. The standard also advises manufacturers regarding preservative effects on adhesive strength and paint compatibility, while purchasers must clarify if treatment is solely fire retardant or combined with preservatives. These measures collectively assure durable, effective, and safe preservative application in plywood.