Frequently asked question on WPC timber deck

1) What is WPC ?

a) WPC stand for Wood Polymer Composite. It is also known as “Composite wood”.

b) It is made from various type of plastic and combined with recycled wood and additives.

c) It is designed to replace wood and conserve forest by using recycle wood.

2) How does it compare against wood?

a) As it does not rot and subject to termite or insect attack, it tends to last much longer the wood.

b) It does not splinter.

c) It does not need to be varnished like wood.

3) What determine a good quality of WPC timber?

There are several issues to look at:

a) The type of plastic or polymer use. Typically they are PP, PE and PVC

b) Type and consistency of wood chips used

c) The correct treatment of wood chips and sizing to make it compatible with the polymer.

d) The correct formulation and ratio between plastic, wood and additives.

e) The correct process and quality control during production

4) What to look out for when selecting and comparing a deck?

a) Colour fastness:

How far will it fade?

Some product will fade 5% after 2 years and some more than 50%.
WPC with good light fastness will last longer and still looks good aesthetically even after 5 – 10 years.

b) Texture and surface:

Will it collect water?

Collecting water encourage mold/mildew growth and increased slipperiness.

Will it be anti-slip both wet and dry condition?

Slipperiness can lead to falls and injuries.
Deck with an embossed surface has much better anti-slip properties even in wet condition.
The higher the value of co-efficient of friction, the better will be its anti-slip properties
Better deck (WPC) are designed to drain water quickly.

Will the surface of deck cool enough to walk on in a very hot day?

Some deck has a better heat dissipation ability than others and can be walk on without hurting the feet.

Will it grow mould/mildew?

Mould/Mildew is both unsightly and can be detrimental to health.
Mould/Mildew will grow on any substrate that retained moisture.
Once it grows, removing it will be very difficult.
Generally, the less absorbent the substrate, the lesser the chance of growing mold/mildew.

c) Case Histories:

How many years?

WPC with longer case histories and excellent record will tend to continue to perform well as the quality would have been proven.

Local references?

Weather conditions differ from country to country and location to location.
It is good to have a local or similar reference as a gauge.
Local reference also allows personal view and feel of the WPC project.

d) Hardness and stiffness:

Harder surface means better scratch resistance
Higher stiffness means less deflection, less fatigue on the deck.

e) Solid thickness.

What is the thickness decking material?

Hollow WPC deck or WPC joist cost much cheaper but can cause many problems.

f) Type of joist or supporting structure and its spacing


i) How far is the spacing between joist?

It depends on the type and thickness of WPC. Assuming WPC is solid and net thickness is 24mm, a PP based WPC which is stiffer and stronger can have a spacing of 600mm and still has a maximum load of 390kg/m2. And for a span of 405mm wide, it can carry up to 975kg/m2. A similar PE based WPC spacing would have to be much closer to achieve the same loading.

ii) Are the joist made of aluminium, wood or composite material?

Polymeric structural composite member are chemical resistant and does not rot. Wood will rot or subject to attack by termites and insects over time. Aluminium will corrode, especially when in contact with water, salts, chemicals and other metallic parts (Electrolytic corrosion). In the presence of electrolytes, aluminium when in contact with dissimilar material, for examples, stainless steel or mild steel screw or even aluminium rivet, creates a potential energy differences between the 2 metallic surface. This results in corrosion taking place faster on the weaker metal (aluminium). Falling aluminium casement windows as highlighted in our newspaper bear witness to this electrolytic corrosion. To prevent this, a Duralac compound has to be applied on the surface of these metals before they are closed.

iii) Will the joist last as long as the deck?

The joist and all auxiliary material used must last as long as the deck. Simply providing the warranty for the deck and not the whole system will not be meaningful.

iv) What is the maximum live load?

Live load depends on the span, thickness and type of deck. Please see Part (i). On a prudent note, the higher the safety factor number given, the more lasting will be the deck.

v) What will be the warranty period?

This depends on the type of decking materials and the auxiliary materials used and project requirement. It can range from 1 year to 25 years (for the better material and confident level of the company).

g) Fastening accessories:

Using nails or screw? Are they mild steel or stainless steel?

h) The correct type of hidden fastener:

Fasteners made from appropriate materials should last as long as the top deck

*Note: a) to h) above determine the performance and characteristic of a high quality WPC timber deck.
A failure in any one item will mean the failure of the entire system.

5) Workmanship

6) Toxicity

7) Maintenance

8) Prices

Prices is a function of many factor.

a) Deck materials
Generally PVC based are cheaper followed by PE and PP in that order.
Quality and location of manufactures also play an important role.
Product that remains as new for years and maintenance free will cost higher to manufacture.

b) Screw and nails
Screw has much better holding power than nail but are much more expensive
Type of metal eg Stainless steel, galvanized steel, mild steel made a big difference in price.

c) Supporting joist
Wood is cheaper than Aluminium and aluminium is cheaper that galvanized steel and then Polyjoist in that order. They also last longer in the same order.

d) Workmanship
Quality workmanship is generally slower and will cost more.

9) As a consumer, how do we know what type of plastic is being use and why is it better?

a) All plastic are made differently based on the input ingredient.
For example PVC (PolyVinyl Chloride) are made from vinyl chloride monomer (VCM) and phthalate. VCM is a carcinogen. Phthalate will leach out over a period of time.
And PVC when burned produces dioxin and HCL gases.

b) No, you will not be able to visually tell which type of plastic is being used.You will have to depend on the integrity of the supplier to tell you.

c) It is known that Polyethylene (PE) based WPC are softer and less stiff. One can actually create a mark with finger nail.

d) Polypropylene (PP, resin identification code 5) is harder and stiffer.