Addressing Moisture Related Problems

Addressing Moisture Related Problems Relevant to Resilient Floor Coverings Installed Over Concrete

Moisture related failures of resilient floor coverings installed over concrete have focused unfairly over the years on the premise that the product itself is at fault or the flooring contractor, perhaps, did not install the product correctly. The purpose of this document is to dispense with such misconceptions and put moisture related problems in their proper perspective. It is not the intent to address each facet in depth and provide absolute curative measures. A greater awareness of the many problems is our goal.

Where concrete slabs rest directly on the ground, installation failures can occur due to the presence of moisture in the slab. The moisture can come from the slab itself if not completely dry, or from the ground where a protective membrane is not present or is ineffective, as the slab comes to equilibrium with ground moisture. A slab may seem dry, but actually has moisture and moisture vapor passing through it and evaporating. Moisture content and rate of transmission will normally vary throughout the year due to climatic conditions and the humidity level in the building. As moisture passes through a slab, it can carry with it alkaline salts and contaminants from the ground and/or the concrete itself.

Above grade concrete floors can also retain moisture and should be tested. Moisture and alkali can cause the following problems after installation:

1.Adhesive deterioration
2.Bumps, ridges, or bubbles
3.Color change
4.Mold, mildew, or bacteria growth
5.Efflorescence (alkali build-up at tile joints)
6.Tile peaking or curling

Any of these conditions could occur at any time after installation if a moisture condition is present (see: "Testing for Moisture in Concrete Slabs"). Proper site preparation, slab construction, and subfloor preparation will make a successful installation more likely. However, since installers and resilient floor manufacturers have little control over these factors, installation failures due to the presence of excess moisture and alkali are generally not warranted by the manufacturer. A review of the manufacturer's warranty is recommended.

The following are offered as guidelines only for the use of the facility owner and/or architect/engineer in preparing specifications in facilities where resilient floor coverings are to be installed. The issuance or use of these guidelines shall not be construed to mean that the Resilient Floor Covering Institute (RFCI), the flooring contractor or the floor covering manufacturer accepts any responsibility for the construction or performance of the concrete slab.

Site Preparation

The single most important consideration affecting resilient flooring installations on concrete in contact with the earth is knowledge and proper preparation of the construction site. Prevention of alkaline moisture transmission through the slab into the adhesive film and resilient flooring eliminates a multitude of potential problems.

Assuming that there is no control over the site selection, there are still many preparatory procedures that can be employed before pouring of the slab begins.

Following is a list of considerations

1.Obtain a geotechnical survey to determine geological strata and water table levels.
2.Survey records for historical data on ground water and flooding situations for the area.
3.Determine water drainage characteristics for the area.
4.Provide detailed instructions for any excavation required.
5.Proper preparation of subgrade where required with appropriate fill.
6.Utilization of 4" (100 mm) to 8" (200 mm) of washed and graded gravel over acceptable sub-grade.
7.Insure positive gravity outflow to resist buildup of hydrostatic pressure.
8.Installation of mechanical means of achieving outflow if gravity outflow is not possible, as with many below-grade slabs.
9.Placement of 1" (25 mm) to 2" (50 mm) of sand over the gravel to prevent puncture of the moisture barrier.
10.Use of moisture barrier of proven performance. Make certain that seams are sealed and the membrane is not punctured during the concrete pour.

Concrete Floor and Slab Construction

After the site has been properly prepared, a moisture barrier with a permeance of less than 0.3 perms (0.2 metric perms), as measured by the ASTM E-96, must be installed under floors on and below grade. This barrier must be resistant to deterioration as well as to puncture during construction and must remain intact and continuous.

The specific composition of the concrete floor should be in accordance with the Guides and Practices of the American Concrete Institute but should have a minimum density of 100 lbs. per cu. ft. (1,600 kg/m3). Information for construction of many concrete floors is contained in the three guides listed below:

1.ACT 302.1 R-89 Guide for Concrete Floor and Slab Construction.
2.ACT 360R-92 Slab on Grade.
3.ACT 223-93 Standard Practice for the Use of Shrinkage-Compensating Concrete.

In enclosed buildings, properly constructed concrete slabs on-grade and below-grade level are stable after they are cured. There will be little lateral or vertical movement at either contraction or construction joints. Therefore if joints are present they should be filled with latex patching compound formulated with Portland cement, fine aggregate, and organic latex.

Experience has shown that properly formulated concrete, specifically with respect to water/ cement ratios and slump factors, will produce benefits of lower porosity concrete.

The concrete must be troweled smooth with a surface tolerance (depression in the floor between high spots) of 5/16" (8 mm) in 120" (3,050 mm) as recommended by the American Concrete Institute.

The concrete floor must be allowed to cure and dry for a minimum of 6 weeks before it is suitable to install resilient floor covering. See Moisture Testing following.

Some additives promoting shortened cure time or easier/longer concrete workability may increase concrete's natural alkalinity leading to increased risks of resilient floor failure if moisture movement transports this alkali to be in contact with the floor/adhesive system.

Testing for Moisture in Concrete Slabs

New or Existing
Several tests are available to determine if moisture is present in concrete slabs. Rubber mats, for one, are placed on the concrete floors for 24 hours. The floor beneath the mat is then examined for dampness. Another method of test involves the use of electrical resistance meters such as the Delmhorst Moisture Detector and the Protimeter Concrete-master.

A widely used and accepted test for moisture in a concrete slab is the anhydrous calcium chloride test developed by the Rubber Manufacturers Association, Inc. in the early 1950s*.

The RMA Moisture Test Unit is designed to measure moisture qualitatively or quantitatively in on-or-below-grade concrete floors only at the time of testing. The RMA test procedure states "that the concrete underfloor when in contact with the earth, must have a moisture barrier sufficiently effective so that the entire floor will pass the following moisture specification, when tested in accordance with the prescribed procedures, at the time of installation of the floor, and also at any future date... and ...The specification shall be that the emission of moisture vapor from the floor shall not be more than 3 pounds (1 .3608 kg) per 1,000 square feet (1.465kg/l00m2) per 24 hours." This method can also be used to determine whether above grade or suspended concrete floors are sufficiently dry to receive resilient floor coverings. Multiple tests are recommended depending upon the size of the installation.

*The Resilient Floor Covering Institute subscribes to the use of the RMA Moisture Test method. It has been widely used and accepted by the flooring industry since the early 1950s, and quantitatively measures the rate of moisture transmission through a concrete slab.

Visual or Qualitative Method
This method suggests that the test unit remain on the concrete floor for a minimum of 60 hours, and then the calcium chloride crystals visually examined for moisture as described in the instructions. The Qualitative Method is very subjective. It may not show moisture which is marginal.

Quantitative or Referee Method
In this procedure, the weight of the calcium chloride and container is determined before the test is started and then reweighed at the conclusion of the test period to determine the amount of moisture present.

It should be noted that any moisture test of on-or-below-grade concrete floors indicates conditions only at the time of the test.

We suggest contacting the flooring manufacturer for specific maximum moisture levels for particular products. If the concrete slab being tested shows excessive moisture or exceeds the maximum of 3 lbs. (1.3608 kg) per 1,000 (1.465 kg/l00m2) square feet per 24 hours, it is generally not recommended that resilient floor covering be installed. Some manufacturers indicate that certain materials will perform under a maximum vapor transmission of 5 lbs. (2.441kg/l00m2) per 1,000 (1.465 kg/l00m2) sq. ft.

If the failure occurs on a new slab, it is recommended that the test be repeated after several weeks. If it is determined that the concrete is completely cured and fails the moisture test, the source of the moisture must be located and eliminated. This may mean diverting water flow away from the building, or excavation around the foundation and installation of a drainage system, or other physical means of removing the moisture from underneath and around the slab. Qualified and experienced persons in this field should be consulted to make specific recommendations to correct the problem.

Actual building/adjacent area construction can affect existing drainage characteristics in ways that may not be predictable.

There are several products designed to treat concrete that are currently being advertised and marketed as a method of eliminating moisture problems. The effectiveness and performance of these types of products is solely the responsibility of the treatment manufacturers.

Subfloor Preparation for Resilient Flooring

1.The concrete floor must be cured, dry (See: "Testing for Moisture in Concrete Slabs"), clean, smooth, level and structurally sound.

2.Any surface materials present such as dust, paint, wax, grease, oil, adhesive residues, asphalt, etc., must be removed by washing or sanding the surface. Allow sufficient time for floor to dry after washing.


a. If sanding is employed, the use of safety goggles and a dust mask is recommended.

b. Unless positively certain that the adhesive residue is non-asbestos containing, you must presume it contains asbestos and the residue must not be sanded. See the RFCI's "Recommended Work Practices For The Removal Of Resilient Floor Coverings" for proper removal methods for asbestos-containing adhesives.

c. Certain paints may contain lead. Exposure to excessive amounts of lead dust presents a health hazard. Refer to applicable federal, state and local laws and "Lead-Based Paint: Interim Guidelines for Hazard Identification and Abatement in Public and Indian Housing" (Sept. 1990) or subsequent editions published by the U.S. Department of Housing and Urban Development regarding:(1) appropriate methods for identifying lead-based paint and removing such paint; and (2) any licensing, certification and training requirements for persons performing lead abatement work.

3.Curing compounds, hardening sealers or parting agents, if deemed detrimental to adhesive bonding (contact manufacturer of sealer or hardener, etc.) must be removed.

4.A scaly, sandy or powdery surface must be corrected as it is indicative of some form of contaminant. A pH reading higher than 9 is an indicator of a potential moisture problem and the concrete should be neutralized.

5.Any cracks, joints, depressions, grooves or other irregularities must be filled and leveled with a good quality, non-shrinking, water-resistant latex patching compound (see: "Concrete Joints"). Plaster type patching compounds are not acceptable.

6.Maintain room temperature between 70°F. (2l°C) and 80°F. (27°C) for at least 48 hours prior to, during and after installation of resilient flooring.

7.The resilient flooring manufacturer should be contacted if more information regarding concrete surface preparation, adhesives or installation is required.

Contributed by Resilient Floor Covering Institute
Copyright © 1995 by the Resilient Floor Covering Institute