Building materials in quantity are a different job from general cargo. They are heavy, they are dirty, and cement is ruined by a single wet hatch.
We carry bagged cement, aggregate, sand, block and steel by the hold load, priced by the tonne. For a site running a programme we will take a standing weekly space so the materials arrive against the pour schedule rather than whenever a boat has room.
Cement is loaded under cover and never under a deck hatch that leaks, and we will refuse to load it in weather that will spoil it rather than deliver you eight hundred bags of set powder. That refusal has annoyed people and it has never once been wrong.
Steel is bundled and dunnaged so it does not shift, because a moving bundle in a hold is a danger to the crew and to everything else on board.