Pete.
Member
- Messages
- 14,142
- Location
- Kent, UK
There’s the issue. I had a chat with a friend today, used to work for the council laid many an exterior path and base. Never once did they use a DPM, and never once did they experience excessive bleed water and long periods before the surface was trowel ready.
With a DPM in place the water has nowhere to go when tamped but upwards. Without a DPM the porous surface below will absorb some of the water which I believe is necessary otherwise too much will rise to the surface. Too many fines at the surface make for a watery like mortar which isn’t very strong.
Months back I laid a small path and built a small set of steps. No DPM was used here. I trowelled that as I have with the other jobs. No dusty surface and no aggregate appearing.
I work on building sites and when any slab is poured onto any porous surface they put a DPM down.