The Pro’s and Con’s of WPC decking in Australia

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There is great debate about what is best between real timber (grown from a tree) as opposed to WPC (wood plastic composite) timbers. Firstly let’s look at what is WPC timber?
Wood-plastic composites (WPCs) are a man-made timber which include the use of wood fibre/wood flour and plastic…these includes PE (Polyethylene), PP (Polypropylene) or PVC (Polyvinyl chloride) plastics. Chemicals and pigments are added and then extruded into planks. The ratio to wood flour to plastic can vary but normally its 45-65% wood to 65-45% plastic. The quality of the product can vary on the amount of wood content and quality of the plastic.

Pros of WPC:

  1. The main advantage is that WPC requires less maintenance i.e. does not need to be re-coated on a regular basis and should be more durable. However it is not “maintenance free”.
  2. It is meant to be resistant to rot and decay from borers and termites.
  3. It made using recycled plastic such as water bottles etc., so are often considered better for the environment.

Cons of WPC:

  1. It does not look like timber. With its beautiful variations in grain and colour, real timber always has a premium look and feel.
  2. It is not as strong as hardwood timber and requires the framework bearers to be closer together to support the WPC planks.
  3. It normally becomes much hotter (in direct sun) than real timber and in hot countries this can make it difficult to walk on in bare feet, especially when used around pools.
  4. WPC expands and contacts (with heat) significantly which can cause problems with the fixings and gaps/ventilation of the decking.
  5. Most WPC can fade, scratch and mark very easily.
  6. Cleaning agents can often mark the WPC.
  7. Water absorption can easily occur through the wood fibres, which in turn can cause fungal attack.
  8. Like all plastics exposed to weathering, WPC becomes porous over time.
  9. Although WPC requires less maintenance than real timber, it is not “maintenance free”. It has been found that most WPC decks require regular scrubbing to remove mildew. Also to maintain a fresh clean look you may need to clean/sand and coat with a stain and sealer once every few years.
  10. Generally WPC is a higher fire risk than real hard wood.
  11. Often more expensive than real timber.

Which is the best decking timber

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There is no perfect timber for decking, however below is some of the “Pro’s and Con’s we have encounted of the more popular species

Name of timber

Pro’s

Con’s

Origin

Merbau

  • Durable/strong
  • Stable/minimal swelling/movement
  • Smooth surface
  • Fire resistance
  • Leaches tannins until sealed
  • Enviomentally not popular as there has (in the past) been widespead illigal felling in Asia
  • S.E Asia

Spotted Gum

  • Beautiful looking grain
  • Quality look and feel
  • Often attracts moisture and mould
  • Prone to rot in lighter heartwood areas
  • Heavy
  • Coatings tend to need to be re-applied more often than other wood
  • Australia

Blackbutt

  • Light colour
  • Often can be prone to splitting/cracking/twisting
  • Can leach black/brown tannins
  • Grain is easily raised
  • Australia

Tallowwood

  • Light colour/great looks
  • Durable
  • Not as durable as merbau
  • Australia

Ironbark

  • Comes in grey/red/brown hues
  • Attractive grain, quality feel
  • Very dense
  • Heavy
  • Often expensive
  • Australia

Northern Box/Forest Reds

  • Interesting mix of grain and colours
  • Does not leach tannins as much as other wood
  • Not as durable as some other hardwoods
  • Can easily absorb moisture and cup/swell
  • Australia

Treated Pine

  • Value for money
  • Plantation grown so enviomentally friendly
  • Light in colour and weight
  • Easy to sand/cut
  • Uneven grain, density and knots
  • Can look and feel budget focussed
  • Sometimes has the green treatments in timber
  • After sanding tends to easily have raised grain
  • Australia but often NZ

Bamboo

  • Enviomentally friendly
  • Interesting look
  • Different
  • Actually a grass not a timber
  • Highly problematic
  • High sugar content means mould problems
  • Absorbs moisture easily and easily swells
  • Man-made with resins means inconsistent quality from different suppliers
  • China

Which is the best coating for my deck?

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  • Water based coatings are easier to apply in cooler temps. (e.g. Intergrain Ultradeck/Natural Stain). Dry faster for quicker re-coats
  • Oil based are easier to apply in warmer to hot temps. (e.g. Cutek and Sikkens) Dry slower, normally re-coat after 24-48 hours.
  • Darker tinted coatings last longer but can be more challenging to get an even finish.
  • Lightly tinted coatings show the grain more, are easier to apply evenly, but are less durable.

There are many different coatings on the current market and there seems to be new products appearing nearly every month, making great new claims.  One thing for sure is, that there is no perfect finish for exterior wood. Australia has some of the harshest weather conditions for timber to endure. High UV, hot temperatures, high rain fall, sea salt etc. all contribute to significant weathering and every product has its “pro’s and con’s”. Most products are designed to either penetrate/preserve the timber or create a protective film over the wood. Below is just our observations of some of the coatings on the market.

Some general rules to consider

Timber Coatings

Pro’s

Con’s

Comments

Totally penertrating coatings/wood preserver

Cutek CD 50 and Extreme

  • Easy to apply, minimal skill required
  • Can be applied on hot sunny days
  • Excellent water repelency
  • Stabilizes timber from cupping/splitting
  • Protects the timber from within
  • Will never peel or crack as no film
  • Less likely to attract mould
  • 1-5 days is required before appling 2nd coat
  • It does not give a deep lustre look to the timber
  • Raised grain can appear after rain on some timbers
  • Very matt/natural looking finish
  • The finish is an aquired taste, some people will not expect such a flat look.
  • A re-coat is required every 9-12 months in exposed areas.

Film forming coatings

Intergrain Natural Stain

  • One of the more durable acylic coatings
  • Provides an attractive semi transparent  finish
  • Dries fast to apply 2nd coat
  • Available at every Bunnings store
  • Easy to use in cooler weather
  • Water wash up
  • Like all acylic coatings, can peel and crack if timber is too hot to coat
  • Good allround timber finish

Intergrain Ultradeck

  • Looks great when first applied
  • Expect to re-coat after 6-8 months in exposed areas.
  • Very popular finish, sold at most hardware stores

Intergrain DWD

  • Can be extremely durable
  • Dimension 4 primer required
  • Can be very difficult to maintain
  • Once it breaks down it de-laminates, bubbles and becomes flaky
  • A complete sand back is often required when this happens.
  • One of the most difficult coatings to remove
  • It can trap moisture into timber, when it breaks down

Cabot’s Aquadeck

  • Budget priced water based decking oil
  • Expect to re-coat every 4-5 months in exposed areas
  • Shiny finish

Cabot’s Deck and Exterior Stain (waterbased)

  • Durable timber stain
  • Hides marks
  • More than 2 coats can look like paint.

Cabots Timbercolour

  • Excellent durability (many years between coats)
  • Hides many marks
  • As it’s a paint it will hide the grain and can hold moisture in timber to cause rot.
  • Great if your deck is looking very tired and you do not mind not seeing the grain.

Spa n deck (Floods)

  • Well proven acrylic coating
  • Very durable when 3-4 coats applied
  • Water repelency teads to breakdown after 6 months.
  • After 4 coats looks almost like a paint (tint hides grain)
  • Can become sticky if re-coated too soon between coats
  • Light finishes tent to look “orangy” in colour

Decking Oils

Intergrain Nature’s Timber Oil

  • Looks fantastic initially
  • Expect to start darkening after 3 months
  • Clean/Re-coat every 4 months in exposed conditions

Cabot’s Natural Decking Oil

  • Budget focused
  • Can be difficult to clean back to bare timber to re-coat.

Feast and Watson (wide varety of coatings both and oil and water based coatings)

Film forming oil based coatings

Sikkens

  • Attractive
  • Durable
  • Great to coat during hot weather in direct sun
  • Well know established brand
  • Expensive
  • Wait minimum of 24 hours between coats (3 coats required)
  • Problematic if becomes wet after coating
  • Can crack when breaking down.
  • Hard to remove by sanding