(About Moisture Control, Adhesion & Liability)
Concrete admixtures are additives mixed into concrete that enhance specific properties of cured and uncured concrete, such as workability, durability, reduced permeability, setting time, etc. This document focuses specifically on Permeability-Reducing Admixtures (PRAs) and admixtures that may negatively affect the adhesion of glue-down floor systems.
Testing Permeability, Moisture Movement:
Admix manufacturers promote PRAs as a way to control moisture by blocking pores and microcracks within concrete slabs. These same manufacturers also maintain that the MFMA-recommended in situ RH probe test (ASTM F2170) is ineffective at measuring moisture and moisture movement within PRA-enhanced concrete. Note: PRAs do not protect against moisture infiltration at post-installation cracks and separations.
Precautions:
Use of Permeability-Reducing Admixtures and admixes in general gives rise to two common questions. 1) Who is legally responsible for floor system damage should the PRAs fail to arrest water within or moving through a concrete slab? 2) Who is responsible for ensuring admixtures perform as intended and do not interfere with common installation practices such as the use of typical leveling fillers, surface grinding, mechanical concrete anchors, or adhesion of adhesives in glue-down products?
Assurance:
Neither MFMA Flooring Contractors nor MFMA Flooring Mills are responsible for ensuring the performance of concrete admixtures, including PRAs, or that they do not interfere with standard installation practices and floor system adhesion. Instead, this responsibility rests with others, admixture manufacturers, specifiers, general contractors, and concrete subcontractors. These parties are responsible for providing a slab that satisfies all project requirements and aligns with contract specifications.
For the protection of owners/buyers, the MFMA recommends that flooring contractors not proceed with installation over an admixed concrete slab without receiving written confirmation of assurance of performance and acceptance of liability, including the responsibility for all repairs or replacement of the flooring system should damage occur due to moisture below the flooring system. The MFMA also advises against giving suggestions or recommendations on concrete admixtures, specifically PRAs, due to the responsibility of others to provide a concrete slab that meets project specifications, including dryness and effective protection against moisture infiltration via post-installation slab cracks. It is important to note that MFMA Flooring Manufacturers and MFMA Flooring Contractor warranties do not cover damage caused by moisture in any form, regardless of source.
As a general precaution, after receiving the admixture company’s written approval, MFMA suggests performing a basic polyethylene film test (per MFMA guidelines) before starting the floor system installation. This test is not intended to validate the admixture's performance, but rather to verify the absence of surface moisture before the floor is installed.
If you have any additional questions, please contact MFMA’s Technical Director at 888-480-9138.
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Disclaimer: MFMA provides general information to architects, specifiers, and consumers. MFMA, its members, officers and agents disclaim any responsibility whatsoever for the accuracy or applicability of these guidelines under all circumstances and conditions.