waterproofing membrane vs vapor barrier 2

[Caribbean]

1. Would you recommend a waterproofing membrane with protection board etc or a vapor barrier beneath the slab on grade in a tropical climate on very stiff clays covered with 1.5m of structural backfill compacted to 95% standard proctor. The slab is a 6" Reinforced concrete.

2. What exactly is the difference between the two.

3. Is visquene (plastic sheeting) an acceptable vapour barrier or waterproofing membrane?

 

[SlideRuleEra]

IMHO, if you have proper surface drainage (directed away from the building), then a vapor barrier is adequate. Polyethylene (Visquene) is a good vapor barrier. In residential construction a 6 mil thickness is the norm. For a commercial building you may want to consider something thicker.

When using a vapor barrier, proper curing of the concrete slab becomes even more important - water cannot quickly out the bottom of the slab. Without curing, the top of the slab dries out quicker than the bottom which leads to curling upward - tending to cause cracking (even in a reinforced slab).

Polyethylene (like other vapor barriers) only slows down moisture transmission, it does not stop it. A water proof membrane essentially stops flow of both water vapor and liquid water. (It does not really stop it, but reduces transmission by several orders of magnitude more than a vapor barrier).

http://www.SlideRuleEra.net

 

[oldestguy]

Hey guys: Note the middle para. of SlideRuleEra. A very true statement and I wish this was publicized more so concrete construction would not result in so many curled slabs!!. I differ slightly in that I think the lower W/C ratio in the bottom versus top controls subsequent amount of drying shrinkage. The wetter the mix, the more she shrinks later. Regardless, the thought is the same.

 

[jike]

We no longer refer to polyethylene as a "vapor barrier" since it is not a barrier. We refer to it as a "vapor retarder" since it reduces the flow of vapors thru it but does not stop it. We use 10 mil thickness for commercial applications.

 

[Caribbean]

Because we have both areas of cut and fill, the Geotech engineer has said the water table will stabilize at the new ground level in areas of cut and 2-3 m below the original ground level in areas of fill. Despite having cut and fill areas we have placed 1.5m of fill and in some areas lean concrete (1000 psi mix) to underside of slab.

Is the waterproofing membrane the better choice for the 6” slab on grade with such varying conditions.

 

[theCorkster]

Carribean:

What's the structure to be used for, and what type of floor coverings are going to be placed on the slab, if any? Some commerical/industrial applications can handle some vapor transmission through the slab during the structure life.

If there are floor coverings planned that will not be permeable, capable of transferring moisture, then the quality of the barrier becomes more critical.

I have encountered visqueen degradation over a relatively short time frame; if you use visqueen, use "virign" material, not created from recycled plastics. Go 10-mil minimum.

As noted by sliderulera, the w/c ratio of concrete and curing have impacts on the long-term performance of floor covering, regardless of the barrier. The entire floor covering process needs to be considered since each aspect, if not done properly, can result in floor covering failure.

 

[tpmanzi]

does anyone have a suggestion for a watertite membrane to be used under a slab and on foundation walls for an application ~3 ft below water table?

 

[SlideRuleEra]

http://www.cetco.pl/e/panels.htm

http://www.SlideRuleEra.net

 

[jike]

Don't forget that if you have a slab on grade that it will not be able to resist hydrostatic uplift greater than it's own self weight unless it is designed as a structural slab.

Volclay panels work great and we have used them in many commercial applications.

 

[golf39]

See Structural Thread 507-179186 Concrete Cover w/Vapor Barrier. Here are some references that address this issue.

http://www.post-tensioning.org/pdfs/sog-faq3.pdf

http://www.nrmca

Concrete In Practice CIP29, Vapor Retarders Under Slab on Grade.
ACI recommends vapor retarders for all slabs which recive moisture sensative flooring, which to me includes most carpets, VCT, etc. The first two references recommend vapor barriers be installed for all interior slabs on grade, which I concur with.
Hope This Helps.