May 1, 2006
As your job progresses, investigation and testing has provided results, and now you and your customer need to make some key decisions. Accurate moisture testing shows that the amount is in excess of floor covering recommendations. What should be done at this point? What are the options available to the customer?
- Wait - If this is a new construction project, or a situation where drying of the slab is a solution, one needs to ask if the floor covering schedule can be pushed back? Can the schedule be shuffled allowing other work to be done to give the concrete more time to dry? Remember, in situ probe testing is a very good way of monitoring this situation.
- Desiccant Dehumidification - speed the drying process by placing temporary equipment that provides dry air reducing the chance of condensation and the overall vapor pressure. There are concerns regarding how old the concrete must be before under going this type of treatment. Investigate fully before moving forward. Dehumidification takes time, normally longer than a few days. The drying process would need to be monitored by moisture testing.
- Correct the Problem - stop the source. If the source is stopped, the slab still may require drying or sealing.
- Change the Floor Covering - Is it possible to utilize a floor covering that may not be affected by the current moisture levels? Ceramic tile, stained overlays, and carpet may all be considered. Please keep in mind, however, that depending upon the situation, problems can occur. Excess moisture and high alkalinity can lead to ceramic joint staining. If stained overlays are considered, be sure that the final protective seal coat is a breathable product. Carpet may be breathable, but it can create an environment ripe for mold / mildew growth.
- Apply a moisture mitigation system.
Selecting Moisture MitigationIf it is decided that a moisture mitigation system should be utilized, proceed carefully. Products in this category have recently grown considerably. There are different types of materials from which to choose. Which one is the best or most appropriate for this particular job? Start this selection process by considering the following:
- What substrate preparation is required by the material?
- What is the turn around time for the system? How does the product / system application affect the job and its schedule?
- What type of floor covering is to be installed? What are the floor covering's requirements of the substrate? How smooth should the substrate be? Is a porous substrate required?
- What kind of area is this? Is this a critical area where shut down in the future to correct a problem is very costly and troublesome?
- What performance is offered by the system? What is the maximum allowable moisture for the system? Whatever the limits are, the moisture must remain within the limits of the system.
- What is the extent of the system's warranty? What specifically does the warranty cover? What is the serviceable life of the system?
- What is the cost of the system? Who is responsible for the cost?
Moisture Mitigation SystemsTypical moisture mitigation systems include:
- Liquid Membrane
- Reactive Penetrants
- Modified Cementitious Overlays
- Dispersive Membranes
- Assembly Systems
Liquid MembranesTopical liquid membranes are typically water resistant acrylics or epoxy based systems. Water resistant acrylics are typically used for less severe problems - maximum emission rates are usually in the single digits. These materials are easy to apply, have less demands on substrate preparation than epoxy and penetrants, and are less costly. Although turn around times and adhesive compatibility will vary, most systems can have floor covering applied directly within 48 hours.
Epoxy systems offer the greatest degree of protection - limits on the vapor emission rate vary between 12 - 25 lbs. depending upon the system. Most epoxy systems have specific requirements for substrate preparation. These coatings require penetration to receive a proper bond to a solid substrate. In most cases proper preparation is steel shotblasting. Shotblasting is the preferred method because it removes the top (usually weak) surface of the concrete (also removing contaminants) while leaving the pores of the concrete open. The International Concrete Repair Institute published a Guide for Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings and Polymer Overlays. This is a great tool for specifiers as well as applicators. This guide defines surface profile and defines how to achieve it.
Preparation and installation of epoxy coatings require more knowledge and expertise than acrylic systems. Most systems extending comprehensive warranties require trained installers to apply the system. The same things that make epoxy systems good for moisture mitigation - a dense, tight seal - make it difficult to bond to its surface. Therefore special primers and / or aggregate broadcast are offered as solution. These type of coatings are not standard epoxy floor coatings, but rather are designed specifically for this use. They are moisture tolerant products that often cure very quickly.
All moisture mitigation systems have temperature restrictions. Epoxy materials are temperature sensitive. Most manufacturers' data is based on temperatures between 70 - 75 degrees F. At warmer temperatures working time and cure time is shortened. Colder temperatures retard working times and extend curing.
Reactive PenetrantsMost reactive penetrants are silicate based systems - sodium or potassium being very popular. Reactive penetrants require an open substrate (shotblasting is the preferred method of preparation) to allow penetration into the concrete. These materials react with the calcium hydroxide and moisture within the concrete to form a gel within the pores, thus reducing the amount of moisture that may pass. The reaction is very reliant on the concrete and its components. For example, use of fly ash can reduce the free calcium hydroxide in the concrete making the sealer less effective. Although these systems are usually the least expensive of the various methods, care must be taken to not over-apply these materials because a film can develop which is difficult to remove and to bond to.
Modified Cementitious OverlaysThese systems are made of epoxy, polymerized cement overlay materials. These materials are very dense, but not impermeable, and are designed for moisture to develop below the overlay. The moisture and alkalinity is kept below the overlay where it will not impact the floor covering system.
Dispersive MembranesDispersive membranes include a fibrous sheet material that is usually bonded to the concrete with a polymer coating. The fibrous mat will wet out and will not allow the moisture and alkalinity to come in contact with the floor covering or adhesive. The system is designed to then allow the moisture to wick-out and dissipate laterally. Specific systems will vary with regard to emission rate control. Most systems require a leveling material to offer compatibility with the floor covering adhesive. Some systems will also offer anti-fracture capabilities. Most of these systems require training to be applied.
Assembly SystemsAssembly systems typically consist of a plastic like material that has dimples or ridges that interlock to be laid over the concrete surface. The plastic is non-breathable and the ridges allow air movement designed to help dry the surface of the concrete. The plastic is usually supplied in sheets which are in rolls or squares. The material is loosely fitted on the surface relying on the floor covering system to keep it in place. Some systems include a layer of wood on top of the plastic which may be directly bonded to. These systems are designed for low levels of moisture and residential applications.
ConclusionThe moisture source can vary, but full investigation should be done to identify it. Complete and accurate moisture testing can help identify the direction that should be taken prior to installation of the floor covering. Careful consideration should be given prior to any treatment installation. Carefully read manufacturers' directions and utilize their technical departments to clarify any unclear issues.
Editor's Note: This article is the conclusion to a four part series on moisture in concrete; for previous articles, please refer to January/February, March and April issues of Floor Covering Installer.