Bamboo-based materials are rich in starch, sugars, and protein — ideal nutrients for mold and decay fungi. In hot-humid regions like Guangdong, untreated bamboo outdoor flooring can develop visible mold within three months. Anti-mold preservative treatment is non-negotiable for outdoor bamboo products. This article compares zinc borate, ACQ, and CCA through two years of field data under Guangdong conditions.
Three preservatives at a glance
| Characteristic | Zinc borate (ZB) | ACQ (alkaline copper quat) | CCA (chromated copper arsenate) |
|---|---|---|---|
| Main ingredient | Zinc borate | Copper oxide + DDAC | CuO + CrO₃ + arsenic acid |
| Mold resistance | Good | Excellent | Outstanding |
| Decay resistance | Moderate | Excellent | Outstanding |
| Toxicity | Low | Low | High (arsenic, chromium) |
| EU REACH | Allowed | Allowed | Banned (civil use) |
| US EPA | Allowed | Allowed | Restricted |
| Treatment cost (CNY/m²) | ¥8–¥15 | ¥12–¥20 | ¥6–¥10 |
| Durability (years) | 3–5 | 8–12 | 15–20 |
| Color effect | Slight whitening | Slight green tint | Noticeable green |
Two-year outdoor exposure results (Guangdong, hot-humid)
| Test item | Untreated | Zinc borate | ACQ | CCA |
|---|---|---|---|---|
| Mold at 3 months | Severe | None | None | None |
| Decay at 6 months | Moderate | None | None | None |
| Surface at 12 months | Decayed, cracked | Slight mold spots | Sound | Sound |
| Decay at 24 months | Fully decayed | Slight decay | None | None |
| Flexural strength retention at 24 months | — | 72% | 91% | 95% |
| Color change | — | Slight whitening | Slight green | Noticeable green |
Zinc borate: eco-friendly but limited durability
Zinc borate is an inorganic flame retardant and preservative with low toxicity and good environmental profile. Its weakness is rain leaching; the protective period outdoors is about three to five years. Regular maintenance is needed (re-coat every two years). Best suited for indoor or semi-sheltered outdoor applications and environmentally stringent projects.
ACQ: the most balanced choice today
ACQ is the mainstream replacement after CCA was phased out. Copper ions provide decay protection and quaternary ammonium compounds provide mold resistance. After two years of exposure, ACQ-treated flooring showed no decay and 91% flexural-strength retention. ACQ durability is roughly eight to twelve years. Note: copper ions in ACQ can corrode metal fasteners; stainless-steel screws are recommended.
CCA: strongest but environmentally restricted
CCA contains arsenic and hexavalent chromium and has been banned for civil building use in the EU since 2004; the US EPA also restricts residential use. It remains usable for non-residential applications such as docks and industrial platforms. CCA protection can reach fifteen to twenty years. If local regulations allow and the client has no environmental concerns, CCA is the most cost-effective choice.
Selection recommendations
- EU market exports: choose ACQ or zinc borate (CCA is banned).
- North American residential projects: choose ACQ (CCA restricted).
- Hot-humid regions (Southeast Asia): prefer ACQ.
- Temperate dry regions: zinc borate can suffice.
- Semi-sheltered outdoor areas: zinc borate is adequate.
- Budget-limited projects: ACQ offers the best value.
Need anti-mold treatment recommendations for bamboo outdoor flooring? We can provide ACQ and zinc-borate-treated samples and two-year outdoor-exposure test reports.
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