membrane under screed??

[Red Kite]

Hi, just laying insulation on 1200g DPM and now looking for a cheap / simple VCL to lay on top of the insulation and under the screed. Looking for a FLAT membrane as I am told the creases you get when you unfold 4m wide DPM / polythene from a 1m roll can cause cracks (plus its a real pain to lay). There seem to be some very sophisticated / expensive membranes / VCL out there but this is just there to stop the screed leaking into the insulation. I think it needs to be 500g / 125 mu. Any suggestions?

Many thanks

[PeterW]

Folds don’t cause cracks - not sure who told you that. 
 

if it’s only to stop screed running through then any cheap plastic will do - check Screwfix. 

[Temp]

+1

 

Doesn't need to be super thick.

 

If it's going to be hot weather  you might consider getting enough to put some on top of the screed as well (as soon as it can be walked on). That will help stop water loss and slow the drying a bit to reduce possibility of cracking.

 

Where two rooms of screed meet at a doorway consider forming a deliberate "crack" (aka expansion gap) across the door. Otherwise you may get a nice curved crack like we did !

 

 

 

[JFDIY]

Check out item number 261995719615 on eBay, I bought a roll for the same purpose as you, but not used it yet.

 

was delivered inside a week at height of lockdown