Selecting the right timber treatment is crucial for ensuring durability and longevity in decks, pergolas, and retaining walls. This guide explores CCA, MicroPro, and LOSP treatments, their H-level classifications (H3, H4, H5), and expert insights from Demak Timber.

Understanding Timber Hazard Levels:

  • H1 & H2: Indoor framing (protection from borers and termites).
  • H3: Above-ground use (e.g., decking, pergolas) 
  • H4 & H5: In-ground use (e.g., subfloors, retaining walls) 
  • H6: Marine-grade timber (wharves, piers).

Types of Timber Treatments:

1. CCA (Chromated Copper Arsenate):

Description: CCA is a water-based wood preservative combining copper, chromium, and arsenic to protect against termites, fungi, and decay. It is a reliable choice for structural and outdoor projects.

✅ Best Uses for CCA:

  • Deck subfloors and joists (H3/H4)
  • Fence posts, retaining walls, and sleepers (H4/H5)
  • House stumps and structural framing (H4/H5)

⭐ Benefits of CCA-Treated Timber:

  • Structural Strength: Ideal for heavy loads (e.g., subfloors).
  • Long-Lasting: Proven durability against rot and pests.
  • Versatile: Suitable for H3 through H5 applications.

2. MicroPro (Micronised Copper):

Description: MicroPro is an eco-friendly wood preservative using micronised copper to guard against decay, termites, and fungal growth. 

✅ Best Uses for MicroPro:

  • Decking and pergolas (H3)
  • Outdoor furniture and landscaping (H3)

⭐ Benefits of MicroPro-Treated Timber:

  • Eco-Friendly: Uses recognised green chemicals.
  • Aesthetic Appeal: Ages to a soft grey.
  • Sustainability: Recognised by green building standards.

3. LOSP (Light Organic Solvent Preservative):

Description: LOSP is a solvent-based preservative suitable for decorative and structural timber. Pre-primed options like Design Pine are ideal for painted finishes.

✅ Best Uses for LOSP:

  • Feature fencing and trims (H3)
  • Pre-primed (Design Pine) for handrails, balustrades, and fascia boards (H3)

⭐ Benefits of LOSP-Treated Timber:

  • Pre-Primed Option: Ready for painting (e.g., Design Pine).
  • Maintains Shape: Fingerjoint or Laminated timber maintains shape better than solid pine.
  • Decorative Appeal: Ideal for visible features.

4. Copper Azole (CA):

Description: Copper azole (CA) is a water-based preservative using copper and azole to protect against fungi, mold, and insects. It has a green tint that weathers to a natural grey.

✅ Best Uses for CA:

  • Decking and pergolas (H3)
  • Garden sleepers (H4)
  • Structural framing and outdoor projects* (H3/H4)

⭐ Benefits of CA-Treated Timber:

  • Effective Protection: Defends against decay and termites.
  • Aesthetic: Natural golden hue, aging to grey.
  • Eco-Friendly: Water-based and virtually odorless.

* We have a product called Low Deck or Xtreme Joist, where you need to achieve a H4 rating for a low-lying subframe.

Summary Table: Timber Treatments Overview

Application Best Treatment Recommended Level
Decking Boards (Above Ground) MicroPro/LOSP/CCA H3
Deck Subfloors & Joists (Structural) CCA/LOSP/Copper Azole* H3/H4
Retaining Walls CCA/MicroPro H4/H5
Windows, Feature Fencing & Decorative Timber LOSP (Design Pine) H3
Handrails & Balustrades LOSP (Design Pine) H3
Marine Applications Marine-grade H6