Patio

That's an insightful question that separates a sound build from a potentially problematic one. ​The short answer is No, a Damp-Proof Membrane (DPM) is generally not required for a standard outdoor patio on an MOT Type 1 base. ​Here is the professional breakdown of why and what membranes are used for in patio construction: ​1. Damp-Proof Membrane (DPM) is Not Necessary ​A DPM (the thick plastic sheeting used under concrete floors in a house) is designed to stop moisture from the ground rising up and into a permanent, enclosed structure. • ​Patios are an exterior, free-draining structure. Your MOT Type 1 sub-base is a crushed stone material that is specifically graded to compact well while still being permeable (allowing water to drain through it). • ​A DPM would be detrimental. Placing an impermeable membrane (like a DPM) on top of the MOT base would trap water and prevent it from draining away. This trapped water would saturate the mortar bedding layer and could lead to issues like frost heave in winter (where frozen, expanding water lifts and cracks the slabs) or accelerated joint failure. ​2. The Correct Membrane (Geotextile) ​If you use a membrane, it should be a Geotextile or Weed/Separation Fabric, and its correct placement is underneath the MOT Type 1. Conclusion: ​Focus on proper drainage and compaction, as these prevent the issues that lead to 'damp' problems in a patio. Ensure your patio is laid with a minimum fall (slope) of 1:80 to 1:60 to direct surface water away, and that your mortar bed is a strong, cohesive mix (often sharp sand and cement) laid directly onto the well-compacted MOT Type 1.

No, you don’t need a membrane under patio slabs — just a solid MOT base, full mortar bed, and proper drainage.

Definitely no membrane needed,100mm of compacted mot and a full bed of wet mortar using sharp sand using mortar mix in mix and tap slabs into laying bed which will create suction sticking slabs down for the foreseeable, membranes are overused and a lot of the time are not needed

No a membrane is not required for Paving. It would be required for a concrete pad designed to hold a shed etc but not when patio Paving is to be laid.

No dom needed outside just compacted mot and good drainage for the water after you laid the slabs

You don’t need a membrane under a patio that’s laid on MOT. The water needs to drain through, not get trapped. As long as your base is solid and compacted properly, and you’ve got a slight fall for water to run off, you’ll be fine without it.