Dpm, required for concrete drive?

jotto · Post: # 29306Post **jotto** Tue Jun 17, 2008 7:48 pm

Following on from here

I now have frame up, shuttering in place and am ready to lay out reinforcing before pouring the mix.

Do I need to lay a DPM? The edges of the slab will be exposed at some points and as its out in all weathers as such, not sure what the membrane will do. Is it required for external applications?

If I do need to lay a dpm, can I just lay one flush with the slab base as if I go up the sides, it will just be flapping in the breeze.....such a n00b!

Mikey_C · Post: # 29307Post **Mikey_C** Tue Jun 17, 2008 8:43 pm

the main purpose of the DPM is stop the moisture being sucked out of the concrete mix to quickly and therefore weakening the mix. therefore omit it at your peril. The flapping bit can always be cut off after curing.

Post: # 29311Post **seanandruby** Tue Jun 17, 2008 9:39 pm

Yep, DPM.

Bob_A · Post: # 29314Post **Bob_A** Wed Jun 18, 2008 9:59 am

I've heard of people wetting the sub base with a garden sprinkler before pouring the concrete to limit the amount of moisture the sub base will take in. Secondary action is that the concrete and sub base fuses together better.
Is that an option or someones excuse to save a couple of quid on dpm.

jotto · Post: # 29315Post **jotto** Wed Jun 18, 2008 12:14 pm

Thanks, Dpm will be picked up later today!

Post: # 29321Post **seanandruby** Wed Jun 18, 2008 8:51 pm

Bob_A wrote:I've heard of people wetting the sub base with a garden sprinkler before pouring the concrete to limit the amount of moisture the sub base will take in. Secondary action is that the concrete and sub base fuses together better.
Is that an option or someones excuse to save a couple of quid on dpm.

Before poleythene was invented that may of been the only option. But have you seen the slabs of yesteryear?. apart from it stopping rapid drying visqueen is also a seperation barrier.

jotto · Post: # 29326Post **jotto** Wed Jun 18, 2008 10:08 pm

seanandruby wrote:
Bob_A wrote:I've heard of people wetting the sub base with a garden sprinkler before pouring the concrete to limit the amount of moisture the sub base will take in. Secondary action is that the concrete and sub base fuses together better.
Is that an option or someones excuse to save a couple of quid on dpm.

Before poleythene was invented that may of been the only option. But have you seen the slabs of yesteryear?. apart from it stopping rapid drying visqueen is also a seperation barrier.

how does visqueen differ from good old fashioned plastic membrane? I was looking at a 4m wide 250 micron? cheap and cheerful roll, was Â£2.20 a metre but if visqueen means doing it right....

Post: # 29652Post **Tony McC** Tue Jul 01, 2008 10:27 pm

Visqueen is a brand name. As long as it's 1000 micron or thicker and DPM grade polythene, it will be fine.