In the next few weeks I would like to try my hand at building a patio. I would like to concrete the formwork stones on compacted ground (still need to be 30 cm higher), and pour concrete over it. On top of that is the substructure, and on top of that are the decking boards. I chose Douglas fir to make the boards. Do they need to be painted or oiled right away?
I wanted to use pressure-impregnated pine as the substrate. Is that possible or should I also use Douglas fir? But I can only get it untreated and it is too fragile for me.