Options for Moisture Membranes and Vapor Retarders

Recognizing the need for an effective means to control moisture and pass the needed testing before flooring is placed, there are three basic options to consider:

• Vapor barriers/retarders: For slab-on-grade conditions, this is the most widely used and preferred solution. Recall that ACI 302.1 is very clear about recommending a more substantial barrier (10 mils) than is commonly used (6 mils).
• Admixtures: For concrete floors either on grade or elevated, silicate admixtures have sometimes been viewed as a solution to control moisture. However, there is a good bit of confusion and misunderstanding on how effective these are. That is because adding in a silicate-based admixture into the concrete or coating the slab with a topical silicate sealant can cause a series of other issues. The first is the possibility of creating a carbonation layer over the top surface of the slab. This can interfere with the adhesion of the flooring or otherwise react negatively. Second, any interruption in the surface treatment creates a breach in that sealant layer. Hence, things like normal saw cuts or expansion/contraction joints interrupt these topical sealers and create a porous condition not only on the top of the slab but on the sides of all of those cuts and openings as well. Therefore, if this option is selected, it must be carefully reviewed with the manufacturer of the product with additional on-site work identified to address the continuity of the system.
• Moisture mitigation: In cases where the moisture levels are determined to be too high to be acceptable, a mitigation strategy is needed in the form of a topical treatment. Note that in a slab-on-ground condition, if it is confirmed that no vapor retarder is present, such a mitigation strategy should automatically be incorporated. If a vapor retarder is present and the results of ASTM F2170 show unacceptable levels of moisture, mitigation is also needed. In some cases, mitigation can take the form of continued drying and retesting, but that will require time and possible construction delays. An alternative is to provide an applied membrane to isolate the resilient flooring from the high-moisture content concrete. The standard in this case is ASTM F3010-18: Standard Practice for Two-Component Resin Based Membrane-Forming Moisture Mitigation Systems for Use Under Resilient Floor Coverings. Two-component resin-based systems are generally considered to be more effective and more reliable than other methods as a means of mitigation.

Moisture mitigation for concrete floor slabs includes using a two-part resinous coating to isolate any moisture in the concrete from resilient flooring.

ASTM F3010 covers the properties, application, and performance of this approach. It provides detailed recommendations and procedures but is not meant to supersede manufacturers’ instructions. It states clearly that this type of membrane-forming, two-component resin system is intended for use only after obtaining high results of relative-humidity testing, such as ASTM F2170 or other relevant or applicable tests. As a product, the membrane needs to provide a very low permeance with a perm rate of 0.1 perms, thus effectively providing a higher degree of protection from moisture than called for in ACI 302.1 at 0.3 perms.

The nature of such membrane systems is that they will exert some stress on the surface of the concrete. Therefore, in addition to moisture testing, the concrete slab surface needs to be tested for tensile strength according to the test method in ASTM C1583: Standard Test Method for Tensile Strength of Concrete Surfaces. Using this testing protocol, the slab to receive the mitigation membrane needs to achieve a tensile surface strength of at least 200 psi. Any area that does not needs to be ground and reworked until it does.

Once ready, the slab then needs to be prepared using shot blasting or scarification. In places where that equipment can’t reach, grinding may be used as a last choice. Any cracks or other irregularities shall be patched or repaired according to the F710 standard and manufacturer’s recommendations. All isolation, expansion, and contraction joints must be maintained. Then, the membrane products should be installed according to manufacturer’s instructions, with or without sand broadcast into the top as appropriate. For quality control, environmental conditions must be maintained, the proper thickness of the material must be achieved, any needed repairs to the membrane must be done properly, and the membrane must be protected until the installation of the resilient flooring.

Specifying the proper option for moisture control in floor slabs will help assure better performance of the flooring over the long term.

Best Practices

Based on all of the foregoing, there are three best-practice recommendations for consideration by design and construction teams:

• Inspections: The flooring contractor and/or design professional needs to inspect the concrete floor before, during, and after its construction. Input should be made to help inform and clarify requirements and conditions for the resilient flooring. If conditions are not met, the concrete floor may be rejected it for suitability unless some appropriate mitigation is performed.
• Testing and core sample access: The flooring contractor should have complete access to all testing processes and results. Similarly, access to core samples of the concrete should be made available in order to be aware of any additions or not to the concrete mix.
• Chain of custody: In a project with many stakeholders, some of the information can get passed to many different hands without a clear understanding of who has what documentation. Therefore, a clearly established chain of custody of all information related to the concrete floor slab will help everyone involved to access the relevant information whenever it is needed.

Conclusion

Providing resilient flooring over concrete necessarily requires different trades with different tasks and priorities. Yet the proper construction conditions must exist for the successful installation and long-term life of the flooring, especially when it comes to moisture and concrete surface conditions. The key to that success is a good understanding of the interplay of the performance requirements between concrete floors and the finished resilient flooring. Full cooperation and coordination between design professionals, concrete trades, and flooring trades can help assure the best results overall.

Peter J. Arsenault, FAIA, NCARB, LEED AP, is a nationally known architect, consultant, continuing education presenter, and prolific author advancing building performance through better design. www.pjaarch.com, www.linkedin.com/in/pjaarch