Polystyrene under concrete?

[iwanttodiy]

Hi

I have fitted underground pipes and just had it all signed off. However as there was less than 300mm between ground level and the crown of the pipes, and my subsurface is concrete, I was asked to sandwich polystyrene as a compressible material on top of 100mm of earth and pour the 100mm concrete over it.

wont polystyrene decompose over time and create a void? It seems to make more sense to sandwich MOT1 to create a more rigid floor.

 

[endecotp]

wont polystyrene decompose over time

No.

 

[iwanttodiy]

Oh, ok. Guessing there’s nothing to worry too much about and just do as BCO says

 

[John D v2.0]

You're not trying to create a rigid floor, you're trying to protect the pipe from movement, which is more important.