Composite Decking Fail

howardtaylor

Hi

First post on here and ive sat on this topic for too long!
In 2021 we built a deck at our property and covered this with composite decking.

Around 18 months after install i noticed the composite was contracting, moving and had started to crack on the surface (see photos). So i contacted the company we purchased from, bearing in mind this was 125sq m of decking so a large area.

After some back and forth, 2 guys came and 'conducted and investigation' into the decking.
They sent a lengthy report, claiming that we had built the deck incorrectly and this was the causation of the damage.

Granted due to our inexperience we used 600mm centres for the joists and not the recommended 300mm centres. So ive always assumed this was my responsibility.

However the more i think about this the more grieved i am and i cant see how the spacing of the joists could account for the cracking of a large portion of the planks? Each crack is along the shallowist part of the material along the top where the honeycomb section is within the plank.

I can see how the spacing could affect the movement between each plank but not the cracking.

Is this my own fault for DIYing the job, or is the supplier trying to get away with selling a faulty product?

Could i speak to citizens advice, some kind of ombudsman or am i destined for this to just degrade until its unsafe?

Now ive vented and wrote a really long post, i'd be interested to hear feedback on this?

Cheers

Aylesbury_Duck

https://forums.moneysavingexpert.com/discussion/6669180/composite-decking-fail

I think you have to accept responsibility for this. Doubling the recommended span has significantly decreased the support each plank is receiving, it's not a linear relationship. Doubling the span leads to four times the stress each board is under (it's a squared relationship). More critically, doubling the span increases the deflection under load by a factor of eight (it's a cubic relationship), so if in the correct set-up, someone walking on a plank caused the plank to deflect downwards by 2mm, under your set-up, that deflection will be 16mm. You can see why, after five years of use, the planks are cracked.

There isn't an ombudsman for decking.

Isthisforreal99

Will be as polite as I can.......clearly not professionally installed.

The poor fitting, not in accordance with manufacturer recomendation, is on you.

Aylesbury_Duck

I think you've got two options here. One is to leave it, accept the cosmetic appearance as it is and hope that the decking holds up for another few years before it becomes unsafe. The other is to take it up, replace it with decking that is compatible with 600mm spacing between joists (if there is such a product) or re-work the frame to halve the spacing and lay replacement decking of a similar type.

born_again

Is this my own fault for DIYing the job, or is the supplier trying to get away with selling a faulty product?

Manufactures give recommendations on spacing for a reason well covered above.

Sorry, but this is fully on you.

DeathByFluffy

Unfortunately this is on you - even if the spacing was unrelated (which as someone else has explained, it's likely not) you've still not installed it as per their requirements so can't expect them to help.

600mm spacing is far, far too wide for most decking materials.

Aylesbury_Duck

Now I'm on a device where I can easily zoom in to the pictures, I think it's clear what's happened. The lack of sufficient support has meant that even without load, the planks' own weight has caused them to bow over time. The different layers that make up the plank will have different strengths and flexibility, and as the shape of the lower layers has changed over time, the top layer, presumably the most brittle and certainly the only visible layer, has broken down.

I suspect that the gaps that have opened up are down to one of two things, or both. If the decking was installed in hot weather and the planks were butted together, then in cooler temperatures they shrink very slightly. Over long lengths both adjoining planks would shrink enough to show the sort of gap seen in these pictures. With there only being half as many joists as there should be, any expansion or contraction would meet less resistance.

howardtaylor

thanks for the feedback. I suspected this might be the general perspective on it. I think i was hoping for a miracle. We built the deck for this exactly the same as we did at my brother in laws (albeit it was much smaller) and that has weathered fine.

Will leave for now, save and most likely replace with a patio in time. Appreciate people making the effort to comment