filling chases containing pipes in concrete floor

[samohtom]

Hi. I have chases in my concrete floor that go down to the damp proof membrane (about 70mm deep) and are about 60mm wide. My plastic radiator pipes are run in these inside slightly larger diameter corrugated pipe, such that the flow and return together take up most of the width of the chase. I've been advised by the installer to fill with sharp sand and portland cement (ratio?), with some aggregate/gravel mixed in. Does this sound about right? Also, I'm guessing cement won't stick to plastic....I'm not sure if I need to pva anything first? Or should I just add plasticiser and squeeze it in all the gaps?

Thanks

Tom

 

[^woody^]

Use sharp or screed sand, 3:1 mix, no need for gravel and a bit wet so it flows in well

Don't worry about it sticking to the plastic pipe, it will still stick to the concrete each side of the channel - dampen them first though