prep for vinyl

Hi, I have looked through the listings but previous posts don't quite give me the answers I am looking for.

I currently have ground floor floating 18mm chipboard which I plan to lay with 9mm ply in prep for karndean/amtico covering over the whole downstairs area.

- The chipboard has a few squeaks, should I screw down the whole floor to joists or just the areas concerned?

- There are some slight dips in chipboard, should I use SLC or sand to give the best result?

- I plan to screw down the ply, is the only reason for not going fully through the chipboard to eliminate the risk of hitting cable/pipes? or does this provide a better fix?

- Is it better to screw in grid pattern or a random pattern over the ply sheets?

The fitter is then going to feather the ply afterwoods.

Thanks for any replies.

 

Get the installer to do all the prep work, it will stop any problems IF they arise in the future.
A floating floor is exactly that.

 

Thanks for the reply and that is an option I am thinking of but the answers would be helpful in any case so I have an idea of what should be done.

'A floating floor is exactly that. ' Does that mean the squeaking cannot be solved?
I assumed floating boards were a construction choice, not a necessity and that screwing them down would generally stop the squeak without any adverse effects.