Auto news on Youtube Dec 31 2018

Why two concrete slabs need black plastic under them? Well, there's some

great reasons. Let's find out why.

So before we begin I just want to be clear

that this session is not about waterproofing concrete slabs and it

isn't about protecting concrete slabs from aggressive soils. Vapor barriers are

the black plastic that builders put under residential house slabs. They do

this for two main reasons:

- to prevent moisture from the soil permeating up

through a slab and into a house; and

- to reduce the amount of water in the wet

concrete being sucked up by the great dry ground when the concrete is first

poured. The black plastic sheet that the reinforcement is sitting on is the vapour

barrier. Waffle slabs require vapour barriers too and here's some photos that

show a few waffle slugs with vapour barriers - again before the concrete is poured.

The requirements to have a vapour barrier come from the NCC - the

National Construction Code (Australia) and the Australian standard AS2870 the

residential footings and slabs standard.

When we call vapour barrier in our

drawings we call it up as 0.2 millimetre thick polyethylene membrane. We show it

on top of a 50 millimetre layer of compacted sand to make it easy for the builder to

have the underside of the slab nice and flat. If you need to buy vapour barrier

you can get it from your local hardware store such as this product from

Grunt - which is an extra heavy duty builders plastic.

Thanks very much for joining us for this video training session. If you liked what you saw don't

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