Wood Protection for Professionals: Chemistry, Mechanisms and Degradation Processes

Professional wood protection begins with understanding the physical, chemical and biological processes that degrade wood. UV radiation, water, oxygen and microorganisms interact in complex ways, accelerating deterioration. This article dives into the science behind wood weathering and explains how modern protection systems counter these mechanisms.

1. How UV Radiation Degrades Wood

UV light — especially UV‑B (280–315 nm) — causes photochemical degradation of lignin, the polymer responsible for wood’s colour and rigidity.

Mechanism

• UV photons break lignin’s aromatic structures

• lignin oxidises → yellowing, browning, then greying

• cell‑wall cohesion decreases

• surface micro‑erosion occurs

• loose fibres wash away with rain

Consequences

• rough, fibrous surfaces

• reduced coating adhesion

• increased moisture uptake

How products protect

• pigments reflect UV

• UV absorbers (benzotriazoles, HALS) neutralise free radicals

• film‑forming coatings block light penetration

2. How Water Moves Through Wood

Wood is hygroscopic: it absorbs and releases moisture continuously. Water transport occurs through three main pathways.

A. Capillary transport

• water moves through pores, cracks and end‑grain

• extremely fast

• primary cause of moisture‑related failures

B. Diffusion

• water vapour migrates through cell walls

• slow but constant

• driven by relative humidity differences

C. Adsorption/desorption

• water binds to hydroxyl groups in cellulose

• causes swelling and shrinkage

Why this matters

• moisture cycling creates internal stresses → cracking

• wet wood is vulnerable to fungal attack

• coatings fail faster under high moisture load

How products address water transport

• oils fill pores → reduced capillary uptake

• silane‑modified systems make cell walls hydrophobic

• coatings act as barriers but must remain elastic

3. How Oils Polymerise

Wood oils are typically drying oils such as linseed, tung or modified alkyd oils.

Polymerisation mechanism

1. Oxidation

   • unsaturated fatty acids react with oxygen

   • hydroperoxides form

2. Radical formation

   • hydroperoxides decompose into free radicals

3. Cross‑linking

   • radicals link fatty‑acid chains

   • a polymer network develops

Result

• oil cures into a solid matrix

• forms a stable but non‑film‑forming structure

• penetrates deeply → excellent adhesion

Factors influencing polymerisation

• temperature

• oxygen availability

• metal driers (cobalt, zirconium, manganese)

• layer thickness

4. How Stains Form a Film

Stains contain binders such as alkyd resins, acrylics or polyurethanes.

Film formation in solvent‑borne stains

• solvent evaporates

• resin molecules move closer

• polymers entangle into a continuous film

Film formation in water‑borne stains

• water evaporates

• latex particles pack together

• coalescence → particles fuse into a film

Film properties

• UV and moisture barrier

• semi‑film‑forming → some vapour permeability

• can crack if stresses exceed elasticity

Why stains sometimes fail

• poor adhesion on weathered wood

• layers applied too thick → internal stress

• moisture trapped under the film → blistering

5. How Fungi Attack Wood

Fungi are the primary biological degraders of wood. They require moisture, oxygen and nutrients.

Main types

• Brown rot

• degrades cellulose

• wood becomes brown, brittle and cubically cracked

• White rot

• degrades lignin

• wood becomes pale and fibrous

• Soft rot

• active under high moisture

• attacks cell walls in soft earlywood

Mechanism

• fungi secrete enzymes

• enzymes break down cellulose, hemicellulose and lignin

• cell‑wall strength decreases

• structural failure follows

How products protect

• preservative impregnations inhibit enzymatic activity

• hydrophobic systems limit moisture availability

• coatings block spores when intact

6. Overview Table: Processes and Solutions

Process	Cause	Effect on wood	Best protection
UV degradation	Photochemical lignin breakdown	Discolouration, fibre loss	Pigments, UV absorbers, films
Water transport	Capillary flow, diffusion, adsorption	Swelling, cracking, rot	Oils, silanes, elastic coatings
Oil polymerisation	Oxidative cross‑linking	Hard, stable surface	Thin layers, oxygen exposure
Stain film formation	Evaporation & coalescence	UV & moisture barrier	Correct thickness, sound substrate
Fungal attack	Enzymatic degradation	Strength loss, decay	Preservatives, hydrophobicity

7. Summary

Professional wood protection requires understanding:

• photochemistry (UV degradation)

• moisture physics (water transport)

• polymer chemistry (oil curing, film formation)

• microbiology (fungal enzymes and decay)

By selecting products that target these mechanisms — pigments, hydrophobic systems, elastic films, biocidal impregnations and deeply penetrating oils — wood can be preserved for many years longer.