How caustic TFR (Traffic Film Remover) can sometimes damage aluminium and galvanised metal

Many TFRs contain caustic alkalis, most commonly sodium hydroxide (NaOH) or potassium hydroxide (KOH). These chemicals are highly effective at breaking down organic grime, but they react aggressively with aluminium.

Here’s what happens:

Chemical Reaction Aluminium is amphoteric, meaning it reacts with strong acids and strong alkalis.

When aluminium contacts a caustic TFR – Reaction: Aluminium + Sodium Hydroxide → Sodium Aluminate + Hydrogen Gas

This reaction:

• Dissolves the protective oxide layer on aluminium
• Eats into the metal underneath
• Releases hydrogen bubbles (causing a fizzing or pitting effect)

Types of Damage

Surface Etching – The first visible damage is a dull, grey, chalky appearance. The natural oxide layer is stripped away, leaving the surface raw and uneven.

White staining / streaking – Uneven application or rinsing leads to patchy whitening. These areas have experienced deeper or uneven etching.

Pitting – Prolonged or repeated exposure produces tiny pits or craters. This is irreversible metal loss.

Loss of polish or shine – Polished or anodised aluminium becomes rough and matte because caustic alkali strips the smooth surface layers.

Why some TFRs are more damaging

• High pH (above ~12) = very aggressive to aluminium
• Hot application accelerates corrosion
• Strong concentrations used undiluted or incorrectly diluted
• Long dwell times allow deeper chemical penetration
• Spraying on dry aluminium increases reaction speed

How to prevent damage

• Use non-caustic traffic film remover or products labeled “safe for aluminium”
• Dilute exactly as recommended
• Never let TFR dry on the surface
• Keep dwell time short (30–60 seconds max for sensitive metals)
• Rinse thoroughly with plenty of cold water
• For polished aluminium, avoid caustic cleaners completely—use neutral pH alternatives – see Non-Caustic TFR