Buried Pipework

[Brian1960]

Hi folks, my son is currently in the process of getting his kitchen full renewed, floor, walls, units etc.
Currently he has copper pipes running along the floor in a trench from one side of the kitchen to the other, the trench/pipes are covered by a bit of timber set into the trench. In time the floor will be getting tiled, I'm concerned about the pipes being permanently buried.
Would it be possible to go from copper to plastic (under the floor) then back to copper? so it can be safely covered.
I've read about running hot/cold in plastic through 40mm waste pipe beneath the floor which can be filled with a weak mortar mix.
Any advice please on the type of plastic pipe I should be using?
I was thinking of PEX as I'd need a gentle curve as it exits the floor at either end.
Any advice will be greatly appreciated
Many Thanks.

 

[CBW]

There’s no harm in using plastic, especially to allow it to be one continuous length.

 

[Madrab]

You can also use cold formers, that will curve the pipe to 90 deg for you if needed Any plastic, PEX or otherwise can be used with them if there's any concern.