Concrete Vapor Barrier

http://www.AsktheBuilder.com founder Tim Carter describes a vapor barrier that's underneath a concrete slab that's about to be poured. Carter reveals why it's mission critical to install a vapor barrier.

Category:

Howto & Style

Tags:

• Concrete Vapor Barrier
• vapor barrier
• vapor retarder
• ASTM-1745
• concrete slab
• Tim Carter
• AsktheBuilder
• Ask the Builder
• home improvement
• installing a vapor barrier

[DaemonEA]

I see two problems there: 1) The vapor barrier is not wrapped up the sides. Big no no. 2) The steel is sitting in direct contact with the vapor barrier. Unless you are doing a 2" slab I don't think that is correct.

[AsktheBuilder]

@DaemonEA Concrete shrinks 1/16th inch for every 10 linear feet. When the slab fully cures, there will be a minimum of a 1/16th-inch gap all around this slab. The vapor barrier at the sides as you want will be virtually worthless. Any water vapor just escapes into the air. The mesh is pulled up as the concrete is poured. You need to see that done in the 4-part Concrete Slab video series I did an hour later. It's right here on my YouTube AsktheBuilder channel.

[neoursa]

It's a good idea, but they should have Sealed the floor barrier to the walls with a watertight sealant. So no part of the concrete touches the dirt and its water tight. Yeah it's picky and most people don't even bother with a barrier, but if you're doing one, do it right.

[echtconservative]

Thank you for the video.

I'll be taking your suggestion in your column to install a high performance vapor barrier in the crawlspace of my old house! I believe another moisture problem is being caused by moisture wicking up through the mortar joints of an abandoned/unusedold chimney whose footing is in the dirt crawlspace and evaporating and migrating into the attic and the drywall that surrounds it. Do you know of any way--short of removal--I might handle this?

[CanadianToolGuy416]

you can also use rigid foam insulation under concrete.  it acts as a vapour barrier and provides some thermal insulation, just remember to tuck tape the joints between the sheets of insulation.

[GypsyKing7]

Thanks