Kwila & Garapa Decking

These installation guidelines apply to all hardwood decking species supplied by Black Forest Investments NZ Limited.
Before beginning, it is crucial to identify whether your decking timber is kiln-dried or air-dried, as this will determine the appropriate spacing allowance. These recommendations should be read in conjunction with NZS 3602, NZS 3604, NZS 3605, NZS 3640, BRANZ Bulletin 489, and any relevant Territorial Authority requirements.

---

Disclaimer

Our decking is manufactured and inspected with care to ensure quality. However, timber is a natural product and is subject to variations in weight, density, colour, grain, and performance. Movement, swelling, shrinking, and surface checking are normal characteristics and should be expected. Installation and maintenance must accommodate this natural behaviour.

---

Transport, Storage, and Handling

• Keep decking timber dry prior to installation.

• Store on bearers (100–150mm off the ground) in a cool, dry area.

• If stored outdoors, cover with a waterproof tarp to protect against weather.

---

Installation Span

• 19mm decking: Install on joists at maximum 450mm centres.

• 21mm or thicker decking: May be installed on up to 600mm centres.

Note: Radiata pine joists are softwood. Ensure they are clean and sound. Screws should penetrate at least 40mm into the joists for a strong hold.
Pre-drilling and countersinking are essential when working with hardwood.

---

Spacing

Decking will either expand or shrink depending on its drying method:

• Kiln-dried decking (16–20% MC) will expand:

  • 90mm x 19mm: Space at 4mm

  • 140mm x 19mm: Space at 6mm

• Air-dried decking (over 20% MC) will shrink:

  • Both sizes: Space at 3mm

Check the label or use a moisture meter to determine moisture content. Proper spacing aids drainage and promotes air circulation.

Note: These are general recommendations — adjust for your local climatic conditions.

---

Ventilation

Good airflow beneath the deck helps minimise cupping and warping.

• Allow at least 450mm ground clearance

• Keep deck perimeters open for ventilation

• In wet or over-water areas, increase clearance and ventilation

• Consider installing a vapour barrier (with drainage slits) and applying coating to all sides of boards

Note: Inadequate ventilation is a leading cause of premature decking failure.

---

Fastening

We recommend stainless 316 steel screws for all hardwood decking:

• 140mm x 19mm decking: Screws are essential — use 60mm screws, pre-drilled, two per joist

• 90mm x 19mm decking: Screws preferred. If nails are used:

  • Use 60mm annular grooved nails

  • Pre-drill to reduce risk of splitting

---

Coating

To reduce surface checking, cupping, and discolouration:

• Apply coating to all four sides of each board before installation

• Ensure boards are clean and dry before coating

• Coating slows moisture movement and extends deck life

• Helps prevent bleeding from timber

---

Pre-Drilling & End Sealing

• Pre-drilled holes and board ends should be sealed immediately after cutting or drilling

• Prevents splitting, checking, and black staining

• Use a compatible end sealer, or a migrating decking stain if suitable

---

Maintenance, Cleaning & Washing

• Clean decking annually with a stiff broom to remove debris and mould

• Keep deck clear of leaf litter, and rotate pot plants or furniture to avoid moisture trapping

Water blasting:

• Use low pressure to avoid damaging fibres

• Always lift nozzle at the end of each pass

• Be aware that coatings may need to be re-applied after water blasting

Chemical cleaners:

• Follow manufacturer’s instructions

• Be cautious of run-off and potential impact on coatings

---

Re-Coating

• Always follow the manufacturer’s instructions for re-coating

• We recommend clear or light-coloured finishes — darker colours can increase heat retention and stress the timber

---

If you require further information, please don’t hesitate to contact us.