Composite decking problems and disadvantages owners report

Composite decking has real disadvantages, and the owners who write reviews are good at naming them: heat, mould on the shaded end, scratches, bounce on wide joists, movement in the heat, and warranties that exclude the thing that went wrong. Most of them can be avoided, and most of the fixes happen before the first board goes down. My advice is to read the list now rather than in the second summer.

Composite decking problems that owners report

Each problem below comes from owner posts on ProductReview and Whirlpool, checked against the makers' own documents, and each one ends with how I'd avoid it.

It gets hot underfoot

The makers admit it. NewTechWood compares its boards in direct sun to concrete on a hot day⁹, and Trex says the darker the colour, the hotter the deck feels⁸. A Trex owner in Sydney wrote that any sun on it "burns the feet"¹³, and an Ekodeck Classic review says it "seriously burnt kids feet"¹⁵.

Avoid it by choosing a light or mid colour for any deck in afternoon sun and by testing samples in the spot, with shade planned from the start. The heat guide goes through each of those.

It costs more upfront

Trex says its own boards cost more than wood at the start⁸, and the clips and the closer joist centres add to that. One Whirlpool member who had to double every joist called the extra timber a cost they hadn't anticipated¹⁹, and another put composite in August 2024 as "a lot more expensive than it should be"¹⁸.

The owners who are happy with it count the oiling they no longer do. One Ekodeck owner says it is not cheap but saves on painting and oiling in the long run¹⁶. A Whirlpool member who upgraded two decks to Millboard set the price against the alternative. Compared with twenty years of sanding and staining, he said, he didn't care¹⁹. I won't put figures in this guide because they move. The prices page carries current state-by-state numbers and the cost per square metre calculator will do the sum for your deck.

It is heavy and it chips at the edges

Owners notice the weight. A Whirlpool member with Ekodeck boards wrote in 2019 that they are "very dense", more so than hardwood²⁰. The same post warns that a board chips if you drop it or knock its end or edge, and that the chips can be "quite large"²⁰. An Ekodeck owner on ProductReview said the thin plastic coating gouged easily when a tool was dropped on it¹⁵.

Avoid it by carrying long boards in pairs and on edge, the way ModWood asks for its boards⁶, and by cutting on a bench rather than across a knee. Keep a couple of spare boards from the same batch for the one that gets chipped.

It bounces on wide joist centres

This is the problem I'd guard against first, because it is the hardest to fix once the boards are down. The Ekodeck owner on Whirlpool said the boards were not too hot "but will sag", and would not recommend them for an upstairs deck unless the joists were run closer together²⁰. A 2018 Whirlpool post describes "huge flex" in a hollow composite board from an importer's trial batch, and the owner ended up doubling the joists across the whole deck¹⁹. Their centres went from 400 mm to 200 mm¹⁹. Another member laid boards on an old 450 mm timber frame against a 400 mm recommendation, after checking with the maker, and reported "a bit of bounce"¹⁹.

Avoid it by reading the joist centres in the install guide for the exact board, including any tighter figure for a diagonal lay, and by not trusting an old timber frame. The joist spacing guide explains why the centres are tighter than for timber. Composite shows every dip in a frame that timber hid.

It goes mouldy in the shade

Mould turns up wherever the deck stays damp. One ModWood owner said that after the heavy rains of 2022 the deck "began to exhibit a lot of black mould"¹¹, and another said it "turns green and extremely slippery every winter"¹¹. A third shifted theirs with "sugar soap and a stiff broom"¹². Capped boards aren't immune. A reviewer on the NewTechWood listing said mould formed on five decks he built with it, and titled the review "mould forms on capping"¹⁴.

The warranty won't help much, and Ekodeck's terms show why. Both its Classic and Designer Series warranties limit mould claims to the first two years and exclude staining from mould and mildew⁴⁵. A capped board is easier to keep clean, but I'd pair it with real airflow under the frame, which ModWood says its boards need to dry out after rain⁶. Then follow the washing routine in the cleaning guide.

It scratches, and capped boards can't be sanded

Trex says none of its product is scratch proof⁸. A NewTechWood owner said the top layer scratches "so easily"¹⁴. One Ekodeck Designer Series owner wrote that people walking across the front porch to the door had left scuff marks¹⁶. The deck had been down two months. What makes this a composite problem rather than a decking problem is the repair. NewTechWood says composite cannot be sanded back like timber¹⁰, Ekodeck says sanding its capped boards causes damage that cannot be repaired¹, and Trex says its decking should never be sanded⁸. Some uncapped boards can be sanded. Ekodeck says you can sand out scratches and marks on its Classic board², though one owner found it hard to match the surface finish even with the coarse paper recommended for it¹⁵.

Avoid it with pads under the furniture, which NewTechWood and ModWood both ask for. For small marks, use the maker's own touch-up product, such as the wax pen NewTechWood names¹⁰.

It can give you a static shock

Ekodeck calls noticeable static rare, but it is strange enough to end up in reviews. A NewTechWood owner wrote years ago about getting "electric shocks when walking on your deck"¹⁴, and a more recent NewTechWood review says the static drives the owner mad¹⁴. Ekodeck's care guide says static builds up in low humidity, that the subframe material and any metal balustrade play a part, and that it is not covered by warranty¹. NewTechWood says the same and suggests an anti-static spray⁹.

Avoid it, or at least reduce it, with the spray the maker suggests. NewTechWood says static usually eases as the surface settles and wears in⁹.

It moves with the temperature

Composite grows and shrinks along its length with the temperature, so the ends need room. One maker's FAQ puts the movement at about 1.1 mm per metre of board as it warms from 15 °C⁹. Over a long run that is a real gap or a real crush. A NewTechWood owner described the movement at the joints along the length as incredible¹⁴. An Ekodeck Designer Series owner said it "expands under heat" and needs the spacing¹⁶, and an Ekodeck Classic owner warned buyers to "make sure you leave sufficient gaps" because the boards move more than you'd expect in warm weather¹⁵.

Avoid it by leaving the end gaps the install guide gives, sized for the temperature on the day you lay, which is how NewTechWood says its boards should go down⁹. Never butt a board hard against a wall or a fascia. The expansion gaps guide has the detail.

It spans less, and it will not take every frame

Every composite board comes with a maximum joist centre in its install guide. ModWood's fixing guide sets one for its decking boards and says heavy concentrated loads may need closer centres⁷. It also asks for a doubled joist, or a block laminated onto the joist, where two board ends meet. An old frame laid out for timber boards may not meet that as it stands, and a new frame needs the extra timber. There is no trick here. Price the frame for the board, not the board for the frame.

It can be slippery when it's green

The worst slip complaint here comes with mould. The ModWood owner whose deck turns green every winter says it gets extremely slippery, and ModWood's reply notes that almost anything outdoors is more slippery when wet. An Ekodeck Designer Series owner put the everyday difference as "a little more slippery than timber but not too bad"¹⁶. The makers publish slip ratings to the Australian standard for pedestrian surfaces. One maker's spec sheet for its capped range lists R10 and P5 ratings to AS 4586, and adds that the surface may wear and that the owner should test it periodically³. I'd treat any rating as the best case, because it can't allow for a film of algae on a shaded deck. Keep the deck clean and the rating has a chance of holding.

The warranty excludes the thing that went wrong

This is the complaint that stings. A Trex owner whose dark boards developed a whitish discolouration was told it was a "dirty deck" situation and not covered¹³. On the ModWood listing, an owner whose boards warped and split says the only offer was discounted boards he would pay for, plus freight¹¹. The maker replied that the warranty had already expired and that the fixing instructions hadn't been followed. On the Millboard listing, an owner whose deck surface had worn through to fibres says the company called it normal wear and tear¹⁷. The deck was thirteen years old.

Read the exclusions before you buy. Ekodeck's Designer Series warranty excludes ordinary wear, including natural colour change, and staining from dirt or mould⁵. It also excludes splitting around screws and improper installation or maintenance, along with any movement of the ground or the structure under the deck. Its payout steps down with age, from the full purchase price in the early years to a small share in the final ones, and install and removal costs are excluded. The lifespan and warranty guide goes through other makers' terms.

Read that way, the warranty covers a manufacturing defect on a deck installed to the guide, kept clean, on a frame that did not move. Keep the receipt and the install guide, and photograph the frame before the boards go on.

Replacement boards will not match

A new board starts out different from the weathered ones around it. ModWood says its colours vary from batch to batch, and that batches of the same colour weather to within a commercially acceptable tolerance⁶. In a reply to one reviewer, it says a new board typically takes about three months of sun to weather in. In most cases, it says, the result is a good match¹¹. That reviewer, writing about a screen built from the boards, said the new ones still hadn't matched after eight months and that the whole screen had to be replaced to get a match. On the Ekodeck Classic listing, an owner who ran three boards short couldn't get more in the same colour, and now has "3 darker boards" in the deck¹⁵. Ekodeck's warranty treats colour variation between boards as normal rather than a defect⁵.

Avoid it by buying spare boards from the same batch on day one and storing them dry and off the ground, as the makers ask⁶. If a repair comes later, replace a whole run rather than a patch.

Before you order

I'd choose a capped board if the deck is shaded or near a barbecue, and a lighter colour if it is in afternoon sun. Design the frame for the board, with the joist centres from the install guide, and treat an old timber frame as suspect until it has been checked. Order spares from the same batch. Keep every document. Then go through the myths guide for the claims you will hear on the other side, and use the deck designer to draw a concept plan with the joists at the right centres for the board you pick.