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.

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. Sealing oil system (optional but premium)
  6. 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
  • As a Gen-X’er I’ve called deck wash “clearasil for timber”for years!
    • “It gets deep into the pores…”

Then:

  • Thorough rinse
    • You’ve read the safety warnings: If such-and-such get’s in your eye, rinse with cold water for 15 minutes. The same rule applies to your deck. A thorough rinse really floods the surface and keeps the water running across it for fifteen minutes.
    • 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
  • 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
  • Example: Sikkens Cetol HLSe

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 — Sealing Layer (Premium System Upgrade)

For best results, build a sealing system using:

  • Sikkens Cetol HLSe (1–2 coats)
  • 3rd coat fills grain and produces a satin finish
    • essential if this is the final finish chosen.

This layer:

  • Further seals timber
  • Creates a stable interface
  • Enhances final coating performance

If this is not the final top coat:

  • Sikkens should be aged 1 month before any other coating is applied.
    • Full hardness of Sikkens Cetol system achieved after 4 weeks.

Step 6 — 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
  • Recoat after 5 years for a smaller work investment → extend surface life to 10 years before resurfacing is required.

Maintenance Reality (What Most People Get Wrong)

Manufacturers often say:

“Must be sanded back to bare timber before recoating.”

That’s not entirely true.

What Actually Happens

  • If coating fails unevenly → must strip back fully
  • If coating wears evenly → can often clean and recoat
    • practically, the deck needs to be recoated before the coating fails.

Older oil systems:

  • Easier to maintain
  • Blend better

Water-based systems:

  • Last longer
  • Less forgiving if patch repairs are needed

Rejuvenation Cycle (Years Later)

When eventually sanding back:

  1. Strip coating
  2. Sand to desired finish
  3. Deck wash
  4. Recoat system

Important:

The original oil stabilisation layer is often still doing its job.

Only reapply penetrating oil if:

  • Significant timber has been removed during sanding

Where This System Applies

Use this method for:

  • New decking installations
  • Full deck rebuilds
  • Decks sanded back to bare timber

Why This Matters

Most contractors:

  • Skip steps
  • Rush coatings
  • Treat decking like paintwork

That’s why decks fail early.

This system takes a little more time and care.

And it delivers:

  • Longer lifespan
  • Better finish
  • Proper timber protection

Final Word

This isn’t just, “Hey, you’ve had the deck done? It’s 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.