Moisture related claims are still a predominant factor relating to today’s flooring failures. The extensive development of water-based adhesive and applied coating technology has created a new dilemma for flooring and applied coating contractors.
Flooring installation and applied coating contractors have been using cementitious underlayment (CU) products for many years to top coat and flatten rough finish or shot blasted concrete, prior to the installation of finish floor covering materials or applied coatings. The increased surface density, tensile strength and smooth finish, make these products the ideal surface for installation of finish floor covering materials.
When CU products are applied directly over a properly prepared concrete substrate, there are very few problems. The CU products can release moisture from both the top and bottom side of the application. If the relative humidity in the building remains below 50% and adequate air exchange is available, the CU should dry in a reasonable time. (8 to 24 hours) Low temperatures, a lack of adequate site ventilation (use negative air flow whenever possible) and high humidity conditions will significantly retard the drying and curing time of CU products.
Most CU materials have a higher density (4000 to 7000 PSI) than the concrete substrates (2500 to 3500 PSI) they are applied to. The density of the CU material and their chemical composition, can create extended drying and curing time requirements. Most CU products are designed to dry and cure completely in 8 to 24 hours, if adequate ventilation, relative humidity levels and temperatures are maintained during the application and curing period.
CU materials contain Portland cement, Calcium Aluminate, Calcium Carbonate, Casein and other chemicals. This combination of ingredients creates the ability of the cementitious material `to flow readily, hence the "self leveling" designation. Due to the amount of water required to enable the CU material to flow properly, the material application process significantly elevates the interior relative humidity of the building, both during and after the CU material is applied to the substrate. The combination of chemicals in CU materials will "bond" moisture into the matrix of the CU material. CU products require a significant & consistent volume of fresh air exchange to effectively reduce the interior relative humidity to a level that will assure the proper drying and curing the CU material in a timely manner.
The lack of adequate airflow and the inability to properly evacuate the excessive relative humidity from the installation site will certainly extend the drying time for the CU material. Just using fans (without outside air exchange) is not a sufficient method to resolve the problem. Without the ability to effectively evacuate the extremely moisture laden air from the building , the fans just move humid air around the job site. The CU material will not commence and continue drying, until the ambient relative humidity of the interior of the building, in the installation area, becomes lower than the relative humidity of the CU material.
Just because the CU material feels hard and appears dry, does not mean the material is dry enough to install adhesive and flooring material. Most of today's adhesives are water based. Adding water from the adhesive to an insufficiently dry CU material, will infuse additional moisture to the CU material and will lead to CU material delamination from the concrete substrate, adhesive emulsification or other moisture related problems.
The CU moisture release issue is greatly exacerbated when the CU is placed over a vapor retardant membrane (VRM). The VRM is designed to dramatically reduce (generally to below 3.0lb/k/24) " vapor movement" from the concrete substrate and will not allow liquid water in the CU to migrate and disperse into the concrete substrate located underneath the VRM membrane. This lack of bottom side moisture release requires the CU to release all of the moisture content from the topside (into the interior of the room) of the CU application. This condition greatly extends the original drying time indicated by the CU manufacturer.
Depending on the buildings internal relative humidity and volume of air exchange, the dry time of the CU material placed over a retardant membrane, could be extended by many hours, several days, or even weeks, in extreme cases. A "hidden" complication exists when the overlay material/VRM assembly’s surface is cooler than the surrounding environment. Cooler surfaces tend to create condensation of the moisture within the CU, slowing evaporation and subsequent drying even further!
If adequate ventilation conditions are present, acceptable application results can be achieved in 24 to 72 hours after the initial VRM/CU application is complete to install the flooring. After the first 24-hours of the curing period, the installation contractor should place fans, and negative air outlets and if necessary, dehumidification equipment should be utilized. If the building HVAC unit is operative and accessible, the HVAC should be used to assist the other airflow and humidity eradication procures.
Some CU material manufacturers have developed significantly more rapid curing and drying products. These products will dry in a more rapid time frame, provided proper ventilation conditions are in effect. The rapid drying & curing materials are more expensive than conventional CU materials. If speedy and properly placed installations are your job requirements, the expense of the higher priced, rapid drying CU material could easily compensate for the additional cost by reducing down time and additional labor costs and providing for a faster completion of the flooring installation.
Prepare ahead of time and advise your client, Architect and the General Contractor of the necessity for allowing the proper amount of time for CU application, drying and curing in the construction schedule. The installer and the client will need to develop budget parameters that allow for the time and equipment required to provide the adequate air exchange conditions necessary for a successful application of CU products.
This article written by Ralph Godfreywas published in the San Diego Daily Transcript on January 17, 2007as part of the Forensic Consultants Association Newsletter. Ralph Godfrey is the Principal of R. Godfrey Consulting Forensic Flooring Specialists - www.floorspy.com.
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