Decking mitre gaps

[Chrisryzen]

Hi there, we’ve just installed new decking and oiled it. But for some reason the inside of the mitred joints have spread open. About 2-3mm gap tapered to nothing. Would I be able to use wood filler in the gap then oil it again. Or would it look obvious that there was a gap there. The boards are 120mm wide so the joint is probably roughly 140mm long. Many thanks

 

[200sols]

Mitred wooden decking will always move like this, filling will look crap and it will continue to move with the seasons.

https://www.deckmagazine.com/design-construction/railings/movement-in-mitered-corners_o

 

[Abyss]

Trying to fill it will look at mess and it'll just fail when the wood moves. A 2-3mm gap is nothing on decking and it'll naturally expand and contract by this amount through the seasons.

I'd just leave it and be confident that the only person that ever notices these things are the ones that installed it!

 

[Jez]

Oil will also not work into filler as it will wood, it'll make it far more noticeable.