Download
1 / 26
330 likes | 617 Vues
Moisture Mitigation. How they work and what to use. Concrete Open or Close System? Open system: Slab in contact with earth Greater opportunity for introduction of water post construction. It is prudent to consider any slab of age to be an open system. (compromised closed system design)
E N D
Moisture Mitigation How they work and what to use.
Concrete Open or Close System? • Open system: Slab in contact with earth • Greater opportunity for introduction of water post construction. • It is prudent to consider any slab of age to be an open system. (compromised closed system design) • Close System: Slab separated with a vapor “barrier” • Recommended within ASTM F710 • Greater protection from introduction of water post construction, but not bullet proof and often times not constructed according to ASTM F710.
Closed System: Unfortunately, a vapor barrier’s purpose from a construction point of view differs from the floor covering industry’s and building occupier’s perspective. In truth, most vapor barriers at the time of slab pour are intended to trap the necessary water required for proper curing. They are typically specified at 6ml polyethylene sheeting which is not an adequate barrier for long term protection from moisture migration.
Grade: Below Grade Moisture Mitigation Systems may not compatible with all slab designs. Care must be taken to select the system best suited not only for the MVER/PH conditions, but also for the type of slab construction, its underlying structure (open or closed), and etc. A perforated pan slab pour above grade is considered an “open” system for example. On Grade Above Grade
Concrete: where is the water? • Why do floors fail? • Types of Mitigation Systems • Potential failures
Water Sources • Free Water • Water of convenience needed for slab finishing • Bound Water • Chemically binds and never leaves • Hydrostatic pressure • Water forced into and upward through the slab • Lateral Migration • Water introduction into the slab from an outside source
Once the slab is poured and finished, “bleed water” runs off and the remaining water within the slab is defined as: Free water • This water is found within the capillaries of the slab and will begin to evaporate if given the correct conditions. Bound water • This is the water that is permanently bound as an integral part of the concrete slab.
How water enters a building HYDROSTATIC PRESSURE
How water enters a building LATERAL MIGRATION
How water moves through a slab As a Vapor Water in the form of a vapor is moved from the bottom to the surface through the capillaries within the slab. Higher porosity (over watered slab) will allow this process to occur more freely. Water comes into contact with the adhesive/slab bond line and attacks the integrity of the adhesive.
How water moves through a slab As a Liquid Water has filled the capillaries completely just as a soaked sponge is completely wet.
Why is moisture a problem? Alkalinity’s effect • As the water vapor migrates up through the slab, it will condense and form liquid water at the bond line between the slab and the adhesive. This solution then becomes alkaline and will harm acrylic adhesives. What is PH? • PH is the measure of Hydrogen ions (acid) or Hydroxide ions (alkalinity) in a water-based system. PH is measured on a logarithmic scale from 0(acid) to 7(neutral) to 14(alkaline). Because the PH scale is logarithmic, each point represents a 10 fold increase in alkalinity. A PH of 9 is 10 times more alkaline than a PH of 8. Gerflor does not recommend a PH higher than 8.5.
Vapor Pressure Even with adhesives that are resistant to alkalinity and moisture, as the adhesive is bonded to the surface of the slab pressure can build beyond the cohesive strength of the adhesive and release. The typical evidence of this is random bubbling. It will usually start in an area or areas and gradually work its way outward as the condition remains or worsens.
Corrective Measures: • Remove and re-pour slab • Topically applied mitigation system • Install slip sheet membrane
Topically Applied Mitigation Systems • Penetrating • Epoxy Coating • Dense Cementitious Overlay • Sealers • Single system approach (adhesive= moisture/ph resistance and bonding agent)
Penetrating Sealers • Penetrating type reactive sealers are liquid applied treatments that chemically react with the concrete reducing the MVER and bind alkali below the bond line. • These are typically silicate in nature (sodium, lithium, or potassium) • Some concrete mixtures will affect the efficacy of these types of sealants in relation to moisture/ph suppression and bonding compatibility with flooring adhesives. • Silicate type treatments are considered by some with much less confidence than other topically applied products.
Epoxy Coatings • There are single and multiple coat systems available. • Many systems designed for very high moisture/ph conditions • Designed to reduce MVER to a tolerable level at the bond line. • Isolates PH from flooring system. • Typical that slab must be abraded through grinding or shot blasting. • Typical that a cementitious over lay is required due to type of adhesive used for the floor covering and/or repair trenching caused by concrete surface preparation. • May include a broadcast.
Dense Cementitious Overlay • Usually requires preparation of the slab’s surface • Primer is applied prior to top coat • Highly densified cementitious layer is poured (may be self-leveling) • Floor patching as needed to bring to floor coverings required levelness benchmark. • Isolates slab from floor covering system.
Top Coat Sealers • Typically used for lower MVER/PH conditions (approx. 8 lbs) • May or may not require slab surface preparation depending upon surface condition of the slab (porosity, existing residues/sealers, etc.) • Designed to reduce MVER/PH to a tolerable level. • Not typically recommended for open slab systems. • May or may not be recommended for below grade slabs. • One of the least expensive systems to apply. • Typically a high solids water based product. • May be “elastomeric”. Caution should be applied to these in combination with certain types of resilient floor covering.
Single System Approach • New adhesive products designed to seal the slab and act as a bonding agent in one step. • Water based acrylic adhesive • Moisture cure urethane adhesive • Economical • Designed for lower MVER/PH conditions • May or may not be designed for certain types of floor covering • May or may not be recommended for open slab systems.
Slip Sheet Membranes • Typically incorporate the use of a urethane adhesive in combination with a low permeance vapor barrier. • Essentially “free floats” accommodating minor cracks and joints. • Typically shot blasting or grinding is not required. • Not necessarily compatible with all flooring systems. • Effectively isolates floor covering away from the slab alleviating build up of vapor pressure. (vapor moves laterally) • PH resistant
Pitfalls of selection • Generally price driven as the discovery of the problem doesn’t occur until just prior to installation of the floor covering. • Lack of investigation. • Incomplete system that does not include accommodations for cracks or joints. • Warranties • System requires “certification” prior to purchase and application • Cost • Incorrect system chosen for existing conditions • Liability/Support if failure occurs • Incorrect application or slab preparation
Who pays? • Conditions above the tolerance level of the floor covering system on new construction projects usually involves incorrect design and/or construction. Unfortunately, this is often not discovered until just prior to installation of the floor covering. As contractors, we can not assess who is the responsible party to cover potential mitigation costs, but it is certain that these expenses should not be absorbed by the floor covering contractor. • Contractors must be very cautious also with existing slabs. Due diligence through careful inspection, investigation, and testing according to industry practices and the mitigation suppliers recommendations is compulsory prior to making any recommendation for a specific mitigation system.
The problem is not a problem… until it becomes a problem. Caution is strongly advised if a contractor makes a personal recommendation for any moisture mitigation system. Choose a system that is appropriate for the conditions and/or potential conditions. Select a system that has a history of performance and customer service in the event of a claim. All to often, moisture mitigation providers are quick to lay claim to contractor error before performing due diligence to discover the actual problem and offer a means to correct it. If a mitigation provider requires training, do not short cut this requirement. If experience or confidence is lacking, it is prudent to provide a list of mitigation providers to the General Contractor, Architect, or End User that they can contact for direct communication and recommendation.
Testing prior to recommendation: Most moisture mitigation systems require traditional moisture testing as outlined in ASTM F1869 commonly referred to as Calcium Chloride tests. These determine the MVER (moisture vapor emission rate) of the surface of the slab at the time of testing. Other tests may also be applicable including the “mat” test, or the In-Situ probe test (ASTM F2170). All tests should be performed by an experienced testing professional (a third party not financially vested into the project) complying to the required testing protocol and completely documenting the results. These results should be forwarded to the GC, Architect, and/or End User prior to selection of the mitigation system to be used.
