I had my decking timber delivered six months ago and some of it has cupped slightly while sitting. It's 140 x 35 pine. When I install it does the curve need to face up or down? Has anyone had a similar problem ? Cheers Marty.
You want the curve to face down wherever possible, so it does not retain water and increase the potential for slippery algae, moss and rot. This diagram shows how timber shrinks differentially depending on the grain direction and the orientation of the board within the log it was cut from. https://media1.britannica.com/eb-media/19/67719-004-A5F7ECED.jpg