By Candace Sofianos King

African Lumber Traders share tips on how best to select and treat your outdoor timber decking.

When considering laying a timber deck to enhance your outdoor entertainment area there are a few fundamental decisions to consider before diving into the project, says Carl Watermeyer, general manager of African Lumber Traders, Cape Town-based timber trader that sells a select variety of timber sourced from all corners of the world.

These factors include durability, stability, sustainability, widths, colour and budget. Weighing up the readily available decking options in the market against these criterions, Watermeyer notes there are three main categories: southern African lumber, tropical hardwoods and thermally modified timbers (TMT).

Massaranduba is a dense and heavy timber perfect for outdoor decking. Credit: Master Decks

Southern African lumber

South African pine (Pinus patula)

The cheapest option available – treated South African pine – is a perfectly acceptable choice that will look great for three to five years, but don’t expect it to look like new forever. Various widths are available, but as with all timbers, go with a thicker (>30mm) option if you are looking for boards that are 150mm or wider.

Eucalyptus (Eucalyptus cladocalyx)

Eucalyptus is a broad term encompassing a number of locally harvested ‘gum’ species like red river, karri and sugar gum. They vary from species to species but they are all relatively hard and durable but are not stable so will move once laid. Seasoning of eucalyptus is notoriously difficult so the timber is expected to dry in situ which causes the movement and cell collapse. The trees often grow in clusters near water which causes the trunks to grow skew, resulting in tension in the boards when harvested. This is a relatively cheap option but more suited where a ‘rustic’ finish is desired.

Zimbabwean / Rhodesian teak (Baikiaea plurijuga)

This species of teak is available from time to time. Although it is unrelated to true teak, it is hard and durable but prone to splits and surface cracking if not treated regularly. If maintained well, the colour is variegated and quite unique. Longer lengths are a premium as the tree is not big and logs over 3m are a rarity.

Tropical hardwoods

Yellow balau (Shorea laevis)

Native to Southeast Asia, yellow balau has been the benchmark for better quality timber decking for a long time. It is hard and durable but tends to crack, splinter and warp over time more than other tropical hardwood equivalents from South America that have come onto the local market over the past eight to 10 years. Pricing is very similar to the Amazon competitors, but sustainability is a real problem with balau. It is listed on the International Union for Conservation of Nature (IUCN) Red List which means that the forest where it is being harvested is poorly managed with concerns of extinction. An additional problem with balau is that any number of similar shorea species may be included in the bundle which may be less durable than initially thought.

Garapa (Apuleia leiocarpa)

This Brazilian yellow coloured timber is often preferred by contractors as it is the softest and easiest to work with of the tropical hardwoods. With the light colour it can get dirty early on but will turn a silver/grey colour if left untreated.

Massaranduba (Manilkara bidentata)

Massaranduba is a very dense and heavy timber from South America. Pricing is very similar to the previous two, but is probably more durable. Expect to break a few drill bits while pre-drilling the screw holes. The rich red colour also turns grey but retains a darker hue.

Ipé (Handroanthus / Tabebuia)

The most expensive of the tropical timbers available on the market but is undoubtedly the most long-lasting and stable so expect to enjoy a beautifully flat and smooth deck for years and years. There is a concern about ipé being registered on the IUCN Red List in the near future as demand, mostly from the American market, has been high for some time and log stocks are running low in the forest.

There are several other tropical species that make an appearance on the South African market from time to time. Importers often bring these in as replacement for massaranduba and garapa when availability of these is restricted. This will be the case for at least the next 12 months with a severe shortage of logs in the Amazon basin due to very late rains significantly shortening the harvesting period. Some of these species include:

Jatoba (Hymenaea courbaril)

This species is widely used for flooring which has more figure and character. Its durability is enhanced by the presence of natural oils in the timber.

Muiracatiara / tiger wood (Astronium lecointei)

A cheaper alternative and more readily available than the others. It has darker streaks, which adds some character to the boards.

Cumaru (Dipteryx odorata)

Cumaru is a very hard and heavy timber and is rightly considered the next best alternative to ipé but availability is also restricted. This is also reflected in the price.

Thermally modified timbers (TMT)

With its rich red colour, massaranduba is a popular South American tropical hardwood used locally. Credit Master Decks

“TMT refers to a process that transforms widely available timbers into very durable and stable wood to be used outdoors by applying very high temperatures in hi-tech kilns. The heat and controlled application of moisture permanently changes the chemical structure of the wood and depolymerises the lignin content in the wood,” explains Watermeyer.

He adds, “In simple terms the sugars are extracted, removing the food on which fungus, mould and other biological bodies feed. The change in the cell structure makes for a much more stable product as water absorption is drastically reduced and durability is unrivalled by other timbers due to the absence of wood sugars.”

Nordic pine and spruce are softwoods most commonly used for TMT decking, notes Watermeyer. “This is a cheap way of installing a high quality deck that will last a lifetime; but although the colour is darker than our SA pine, they are still soft and have a very similar grain so may mark in high traffic areas.

“Ash goes through an intense TMT process so changes colour from the normal blonde to a dark brown hue but still retains the beautiful figure for which ash is known. Thermo ash and ipé are the only two timbers listed here that are Class 1 for durability according to European standards classification so longevity and stability are key factors. Ash has the added advantage of being available in wide boards up to 150mm and still able to be fixed by means of a non-visible clip system with no risk of cupping or warping – a rare and wonderful characteristic.”

Durability versus budget

As a rule of thumb, the cost of the timber bares a direct relationship with the longevity of the product, notes Watermeyer. “So chromated copper arsenate (CCA)

Thermory ash pool decking in Sea Point, Cape Town installed by Timber Connection. Credit: Timber Connection

treated South African pine would be the cheapest option but don’t expect your deck to look like new forever; while at the other end of the scale, ipé and Thermory ash will last a lifetime with very little or no maintenance.

“The problem with outdoor decks exposed to the elements is that deterioration is a constant process, so if a deck is guaranteed to last 10 years, it won’t look new in year nine and will look like death in year 11. The ageing process starts from day one and timbers that crack or warp will show signs early and slowly accentuate over time. It is therefore desirable to extend your budget as far as possible to build the best entertainment area possible. Rather reduce the size of the deck than reduce the quality of the wood you choose.”

In terms of using decking clips, Watermeyer says he has never advocated the use of a hidden fixing system as wood swells and contracts from season to season which will place strain on the tongue holding the decking plank down as the wood moves – this is especially the case with wider boards. He notes the exception to this rule is with the advent of TMT decking. The stability is unparalleled in this decking so feel free to use clips if you don’t see screws as part of the charm of the deck, Watermeyer advises.

When it comes to substructure, most decks built in South Africa have CCA treated South African pine substructures. “Be very careful going this cheap route. It’s not worth taking shortcuts on the hidden parts of the deck to save a buck and have it collapse or just sag a few years down the line while the upper surface is still perfect,” Watermeyer notes.

Take care of your timber deck

Timber deteriorates due to fungus eating away at the fibres of the wood so be careful to install in a way that doesn’t trap moisture on the timber, highlights Watermeyer.

“Although the sun will dry the top boards of your deck as the rain fades away, the substructure will still be in the shade and will remain damp and therefore is a fungus breeding ground if air movement isn’t allowed to dry the unseen timber below. The best solution is to use the same timber below as in the top structure but unfortunately this will cost more, although long term quality is assured.

“Remember to allow for the free flow of air, not only between decking boards, but also around the bearer beams to ensure evaporation of moisture under the deck. Also, along south facing walls where the deck isn’t exposed to much sun, moisture lingers longer and fungus grows very easily. This makes the deck slippery when wet and also shortens the lifespan of the wood,” highlights Watermeyer.

Watermeyer adds that it’s also essential to leave space between the boards to allow for expansion which will close the space between the boards in wet winter months as well as between the decking boards and the substructure, he adds.

While the choice, planning and maintenance of timber decking takes time, money and effort, the natural and potentially carbon negative beauty of a wooden deck outweighs it all. If it is carefully constructed and correctly taken care of, a deck is for life.