Pergola Decking Advice Needed

[Mikegtr]

I am having old decking replaced on my old pergola which is pretty old. The original has thin plastic sheet ( thin 'dustbin' plastic sheet) put down for membrane--not the proper membrane as used today.

My question is:
Can the proper membrane--as used today--be put down over the top of the thin plastic sheet? or doesn't it make any difference? Just a sort of double layer?

Look forward to your replies.
Many thanks.

 

[saffer]

hey mike. recently done some decking myself. would recommend putting down a water permeable membrane to aid drainage. perhaps some gravel on top for good measure. so in short, i would rip up the plastic sheet.