All aboard for the delights of composite decking

Kya deLongchamps has warmed to the potential of plastic and covers everything you need to know if you’re planning to install a new deck.

IF ANYONE had asked me last week about composite decking, I would, without hesitation, have bounded to my environmental concerns.

How and ever — today, spattered lightly in walnut-shaded deck reviver with a splinter in my undercarriage and the solid beginnings of a middle-aged back, my green deck ideals are slightly underwater.

That said, it’s been about seven years since I tripped the boards, brush in hand. Wood decking has been good to us. We replaced the original wrap around of 18 years, six months ago, and every single pressure-treated board (all perfect structurally) went into the garden of a neighbour in a chicken house, a log store and to clad several raised vegetables beds. Quite properly, none was burned. Only that we left the new deck to green up just too long — a couple of lashes of oil and it would have been ship-shape.

Plastic Fantastic

Plastics around the exterior of our house and gardens are nothing new —windows, fencing, seating, facias and soffits — we’re in familiar territory. Composite, is a carefully chosen word, as quality faux wood decking is a not just plastic but a blend of modern, high-density polyethylene (HDPE) polymers and wood dust.

Properly installed, it looks great and, until your bare tootsies feel a slight chill and revealing glide, it’s reasonably convincing.

Early varieties of fake decking were notorious for chipping and were not sufficiently UV resistant to hold up for more than a few seasons.

Now, you just wash down your plastic fantastic and you’re done. With up to 25 years of fade resistance, and no screw heads on show, the performance, as guaranteed, is impressive.

It’s worth noting that in board form, elements of wood polymer can be replaced, so it can be repaired in the conventional sense — a problem often levelled at plastic made into anything substantial.

The texture of good composite decking has reasonable heft, a visual honesty and the latest products can be worked with woodworking tools. For a DIY, entry-level soul, the composite installation is relatively straightforward.

Composite construction

Composites saw well, drill out perfectly and don’t twist and warp. There’s no wastage with a delivery of perfect, synthetic boards and finishing strips. It’s the groundwork and any wood support below decks, that may sink that rookie project.

The added flexibility with rigid strength of composite wood is great, but we don’t want a bouncy deck in any material. Composite deck can be laid flat down on a patio but only on dedicated support rails (also in composite). It’s similar to floating a laminate floor — with clips and grooves that marry up.

Level ground, 150mm below the DPC [Damp Proof Course] thresholds to your doorways — and you’re ready. Using just support rails straight down on the ground, leave an expansion gap of 10-15mm from the end of the beams to the house wall to allow water to escape, and check the maker’s instructions on gaps between butting boards and rails.

Height is not adjustable

Remember that the supporting structure at any real height from the ground, will be as standard (that is, in wood) and joined to the house via a wall-plate. After the standard ground preparation (levelling and installing a geo-textile to hold back weeds) — key in the price for your chosen height in pressure treated joists, posts and so on.

If you don’t know what you’re doing, have a professional prepare the ground and put in the wall-plate, posts and joists — with levels, drainage, structural strength and safety — this is not something to get wrong. Wishbone patterns, decorative borders and colour changes? Again, examine your skill set.

Putting the deck down on joists or on the patio, a 10cm concrete base with a 1:80 gradient/ fall away from the house would be appropriate. Straight down on the ground out in the garden without a rail? Dig out the turf, level the area, and add 40-50mm of gravel over the geo-textile weed barrier.

With the support ready, all you need is spirit level, mitre saw; electric drill with appropriate drill bits; tape; a jigsaw and power screwdriver.

Some deck products have a very obvious ‘grain’ direction and will tell you to allow some seasoning to bring planks to the same colour —they really should be the same colour from the beginning.

Plan the deck to take whole deck boards to cut down on cuts and joint complexities. Step surfaces, and decking in composite with wood rails is a great combination, with the authentic touch of timber under the fingers and the durability of composite underfoot. Skirting can be used below the deck, if you fancy.

Price wise, composite deck boards by a reputable company like WhiteRiver or Trex (delivered ex installation), compare to entry level hardwood prices at around €30 for a 3.6m slender width of 135mm boards per piece — roughly €60 per square metre.

Hollow form boards are cheaper than solid boards and the installation rates would compare with wood if you have the professionals handle it. Shorter Trex boards from B&Q are reasonable at €102 for a pack of four 2.4m/140mm solid boards. Dead easy? Choose a clip down square tile system, from €6 a tile, also from B&Q.

Deep 60mm finishing strips of 4m length (cut to suit) start at €15, but you can of course use leftover boards as skirting too. Buying in bulk form, a builder’s supplier online or off, should see that price down by as much as 5-10%, great if you need 25-40 boards plus.

Extras on top

Additional costs include the set of dedicated screws to attach the supporting rails down to the joists (a bit for your drill may be included) and secret-fix clips that attach on a side rib and secure the boards to each other and the edges.

The clips ensure a uniform 7mm or so gap for drainage. Allow around €15-€18 per 2.5msq of deck for these essentials. Most boards come double-sided, so you can choose from a wider or finer groove when you install; it’s simply a preference thing.

Common colour choices include dark brown, dark graphite grey, light brown, hunter green and a pale dove grey.

Composite decking is resistant to mould and mildew, but not impervious to it. If organic rubbish and slimy dirt collect, it can get green. The beauty is, it washes down beautifully with a soft long handled brush, and once clean, you’re free to pour the margaritas and recline.

Otherwise tough and shock resistant —drop a cigarette or smoking charcoal on faux wood decking — it can mark. You certainly would not want to inhale those sophisticated fumes.


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