Moisture Protection/Flooring - Vapor Emission Barrier

Many General Contractors have gotten into trouble when backed vinyl, carpet tiles, sheet vinyl, seamless resinous flooring, rubber, PVC, or nonporous flooring has been installed directly above a concrete slab that has not fully cured yet. This causes bubbling or delamination to occur because the moisture can’t escape the slab resulting in expensive flooring replacement.

It has been our experience that all new concrete slabs whether on grade or elevated, will not dry out enough to meet the stringent requirements of the flooring manufacturers. It can take years for the concrete slab to reach a point to be within flooring manufacturers’ limits for vapor emissions, especially in high humidity areas like the Southeastern US or along the coast. These requirements are usually set at a threshold of 3#/sq ft/24 hrs. The unit of measurement is not a percentage.

The vapor pressure that occurs from the hydration process has nothing to do with the vapor barrier beneath the slab on grade. Even if you have a Stego wrap or 10 mil plastic vapor barrier installed before the slab on grade is poured, this situation will still occur as the concrete slab cures and moisture escapes from within the concrete. However, it is likely that without a vapor barrier below the slab on grade that moisture from the soil will reach the underside of the slab on grade and increase the probability that the concrete slab will remain moist for a longer period.

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So, in retrospect, installing a vapor barrier below the slab is good practice. In Southern California, specifically Los Angeles County, there is also a concern with methane in the ground and as such many projects require a methane barrier. That will be the subject of a future bulletin.

We should always require the flooring subcontractor to take measurement readings on the slabs at a couple of different stages of the construction. The first test perhaps as early as 28 days after the pour (to establish a baseline) and the second two weeks prior to the planned start of flooring. If the test results are not sufficient to achieve the required results for the flooring manufacturer, which is a very high probability, then it will be necessary to apply a vapor emission barrier membrane to the concrete prior to installing the flooring. Bergman should include a vapor emission barrier cost in the estimate on all projects where there is nonporous flooring.

The best way to achieve a moisture level within the required guidelines is to energize the building air conditioning systems which will assist in dehumidifying (or drying out) the slabs. This goes for not only the slab on grade but also for the elevated deck slabs as well. However, the schedule will often not allow for the air conditioning to be fully operational prior to installing the flooring.

One trick to assist with the curing or drying out of elevated slabs on metal deck (in a structural steel building) is to install vented deck. Add fans to pull/move air over the surface. That allows some of the moisture in the concrete to escape through the bottom of the deck/slab.

As a standard practice to ensure that healthcare is not interrupted. Mapei brand products are used by US Renal Care; the products are:

1. Mapei Planiseal MVR

2. Mapei Planiseal VS Fast

We need to plan for a vapor emission barrier on top of the slab in the estimate as well as in the schedule. Researching a product that we have used in the past from Koster, we find that the cost for the material is roughly $300/gallon and that one gallon spread at a thickness of 11 mil results in coverage of 150 sq ft per gallon. That results in a material cost of $2/sf. Labor costs vary greatly depending on the amount of area to be treated. A fully burdened (labor, material, equipment, tools, OH&P) subcontracted cost can easily run $8/sf.

This is an epoxy product and therefore requires the installers to wear proper eye and skin protection as well as respiratory protection. The area must be well ventilated, and, in fact, the work should be performed on second shift when no one else is in the building. Assign the responsibility for the ventilation requirement to the subcontractor.

Scheduling the Koster Epoxy Product

The Part A and Part B components are mixed on site in a bucket and only have a pot life of 12 minutes, so the material needs to be spread on the floor immediately. It has a cure time of 12 hours. It should never be applied to a concrete slab that is less than 7 days old.

The surface prep requires shotblasting. This portion of the work can be done during normal working hours. Grinding the surface should only be used at corners where the shot blasting cannot reach. Acid etching should never be used. Do not clean the area with sweeping compound. Vacuum the loose cement after the shot blasting. The subsurface must be clean and free of debris, dust, grease, oil, leveling products, curing compounds, and sealers.

Up to a 15-year warranty can be obtained if the installers are trained/certified by Koster.