Ultimate Deck Coating System (SEQ Conditions)

How to Build a Deck Finish That Actually Lasts

The Problem Most Decks Have

Most deck coatings fail early because the timber underneath was never properly prepared.

In South East Queensland, this is made worse by merbau (kwila)*—a timber loaded with tannins that:

  • Bleed when wet
  • Stain surrounding surfaces
  • Interfere with coatings if not properly removed

Once tannins stain concrete or masonry, you’re not removing them—you’re managing the damage.

So the goal is simple:

Stabilise the timber first. Then build your coating system on top of that.

*Note: This guide applies to all timber types used for decking. The steps outlined below are particularly important for tannin rich timbers like Blackbutt, Western Red Cedar, Merbau/Kwila and Jarrah as well as oily timbers like Spotted Gum, Teak and Rosewood.

The PHMS System — Overview

This is a layered system, not a single product solution.

  1. Remove tannins and contaminants
  2. Neutralise and brighten the timber
  3. Allow to properly dry
  4. Penetrating oil (timber stabilisation layer)
  5. Final coating (appearance + wear layer)

Done properly, this system:

  • Protects the timber long-term
  • Extends coating life significantly
  • Produces a far better finish

Step 1 — Tannin & Oil Removal

Fresh merbau must be treated.

Use a tannin and oil remover (alkaline cleaner):

  • Aggressively lifts tannins and surface oils
  • Essential before any coating system begins

This step is non-negotiable for new timber.

Step 2 — Deck Wash & Brightening

Follow with a deck wash solution:

  • Typically contains oxalic acid
  • Often supported by citric acid as a brightener

This step:

  • Neutralises the alkaline cleaner
  • Restores timber colour
  • Prepares the surface for coating

Process

Mix deck wash solution according to directions on the bottle.

Apply to deck surface with a soft bristle broom or spray pack.

Keep deck surface continually wet with deck wash solution for 15 minutes. Areas that dry out during the process must be re-wet with solution.

After 15 minutes or more has elapsed, thoroughly rinse deck surface.

  • Notes:
    • A thorough rinse really floods the surface and keeps the water running across it for fifteen minutes.
    • Hose down the deck along the length of the boards. Work systematically.
    • A normal garden hose is usually the best. Only use a pressure washer with a wide fan jet to avoid surface damage.

Step 3 — Drying

Allow timber to dry:

  • Minimum 24 hours in good weather
  • Longer if conditions are humid or shaded

This ensures:

  • Moisture content is suitable
  • Even if the surface looks dry it can take longer for water beneath the surface to fully evaporate
  • Coatings will bond properly

Step 4 — Penetrating Oil (Timber Stabilisation Layer)

This is where most systems stop short—and why they fail early.

A penetrating oil layer:

  • Soaks into the top 1–2mm of timber
  • Sets hard within the fibres
  • Acts as a moisture and contamination barrier

Options

Traditional System (High Performance)

  • 50/50 Natural Gum Turpentine + Boiled Linseed Oil

Used for centuries by:

  • Boat builders
  • European trades
  • Traditional timber craftsmen

Benefits:

  • Deep penetration
  • Breathable finish
  • Strong resistance to moisture, mould and rot

Natural gum turpentine (plant-derived) performs very differently to mineral turps—it carries the oil deeper into the timber.

Commercial System

  • Solvent-based timber oils

Benefits:

  • Consistent formulation
  • Proven durability
  • Easier repeatability for contractors

Curing Time

  • Boiled linseed oil: minimum 48 hours
  • Heavier solvent-based oils: up to 7 days

For water-based topcoats:

  • Allow a minimum of 7 days before overcoating

Step 5 — Final Coating (Wear & Appearance Layer)

This is the visible finish.

Typically:

  • Water-based acrylic coatings
  • Flexible, durable, UV resistant

Recommended Systems

  • Sikkens BLX-Pro
  • Intergrain Ultradeck (Oil or Stain variants)

These coatings:

  • Provide the look
  • Take the wear
  • Protect the system underneath

Performance Expectations

Oil-Based Systems Only

  • ~1 year exposed
  • ~2 years covered

Full System (Oil Base + Water-Based Topcoat)

  • Up to 10 years service life
  • Water based finished last a long time however manufacturers generally advise they cannot be successfully “serviced”. One their service life is done they must be sanded back and completely removed before starting again.

Final Word

This isn’t just, “Hey, your deck is looking good.”

It’s about making sure that years from now your deck is still looking good.

Get more enjoyment from your outdoor living areas, everyday.