The destructive process of concrete slab construction

These extracts from the appendix of a 1998 ASTM vapor barrier specification indicate that some ASTM committee members believe that vapor barriers will not survive construction.

Rebar fabrication can involve welding, foot traffic, and sharp edges of cut rebar and wire, On most large projects, steel rebar is installed over the vapor barrier.

Source: www.constructionphotographs.com (#a00305

Prior to the concrete pour, plastic, wood, or steel “chairs” are inserted at rebar intersections. 

Source: www.constructionphotographs.com (#a00322-section zoom)

Sometimes large equipment is driven over the vapor barrier.

Source: www.constructionphotographs.com (#a00305-section zoom)

Concrete mix trucks weigh 25,000 to 30,000 pounds, and carry 40,000 pounds of mix.

Source: www.constructionphotographs.com (#a00308)

 Concrete mixes contain aggregate with sharp edges.

The edges and points create added likelihood of vapor barrier punctures.

Source: www.istockphoto.com (#143034)

During concrete placement, numerous workers stand ankle deep in concrete, and can damage the vapor barrier every time they put their foot down

 

Source:www.constructionphotographs.com (#a00467)

While consolidating concrete, there is vigorous use of sharp-edged tools.

Source: Portland Cement Association (Vol. 2 #34)

Internal concrete vibrators are also used during concrete consolidation

Source: Cement Association of Canada (EB101-7 Fig. 11-11)

Specifications of one major vibrator manufacturer show impact force of 3200 lbs. on their 3” head diameter model.

Sources: Wycotool (Vibrator Drawing) Vibco (Vibrator Specifications)

Finally, there is the possibility of INTENTIONAL vapor barrier damage.

Ironically, quality control
instruments like this depth probe might damage vapor barriers.

Source: Portland Cement Association (Vol. 2 #162_4)

 

 

 ASTM E 1643 – 98, section 6.3:

   “Avoid use of stakes driven through vapor retarder”

  PCA Engineering Bulletin 075, page 15:

“The practice of intentionally punching holes through a vapor retarder to allow bleedwater to exit the slab bottom is unacceptable because it defeats the purpose of the membrane.”

Conclusion: Vapor barriers are a proven method to reduce vapor transmission.  But with the likelihood of multiple punctures, nobody should depend on a vapor barrier to help waterproof a structure.

 

Nor should anyone depend on vapor barriers as a termite barrier.  Puncture damage creates entryways for 1/50th inch wide subterranean termites.