Moisture Sources Water of Hydration Water required to complete chemical reaction Water required to complete chemical reaction Typically considered ~25% of cement by weightTypically considered ~25% of cement by weight Water of Convenience Water used for ease of workability and placement Water used for ease of workability and placement Usually another 25% to 40% of cement by weightUsually another 25% to 40% of cement by weight Moisture Vapor Transmission (MVT) Water of convenience evaporating Water of convenience evaporating 4” slab poured at.50 W/C evaporates >½ gallon per sq ft.4” slab poured at.50 W/C evaporates >½ gallon per sq ft. Water coming up through the concrete from under slab Water coming up through the concrete from under slab
Water in the Slab Free water This water is found within the capillaries of the slab and will begin to evaporate if given the correct conditions. 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. This is the water that is permanently bound as an integral part of the concrete slab.
Concrete Curing/Drying All concrete requires time to “dry”. 4” concrete slab with a 0.5 w/c ratio over an impermeable moisture barrier will take approximately 92 days to get to a suitable level for wood floor installation 4” concrete slab with a 0.5 w/c ratio over an impermeable moisture barrier will take approximately 92 days to get to a suitable level for wood floor installation Reference: “Are your slabs dry enough for floor coverings?” By Bruce Suprenant and Ward R. Malisch, Copyright 1998
Drying of Concrete Thickness of concrete slab also impacts drying time
Open or Closed System Open system: Slab in contact with earth Greater opportunity for introduction of water post construction. 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) It is prudent to consider any slab of age to be an open system. (compromised closed system design) Closed System: Slab separated with a vapor “barrier” Recommended within ASTM F710 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. Greater protection from introduction of water post construction, but not bullet proof and often times not constructed according to ASTM F710.
Basic Concrete Slab Construction Site evaluation Compressed soil Compressed soil Large aggregate (capillary break) Large aggregate (capillary break) Smaller aggregate Smaller aggregate Moisture barrier specifications 0.010” thick reinforced film 0.010” thick reinforced film Exterior Drainage and Landscaping concerns
Closed System A vapor barrier’s purpose from a construction point of view differs from the floor covering industry’s and building occupier’s perspective. Vapor barriers at the time of slab pour are intended to trap the necessary water required for proper curing. Not an adequate barrier for long term protection from moisture migration.
How Moisture Moves Through a Slab On grade concrete Capillary & MVT Capillary & MVT Below grade concrete Capillary, MVT & Hydrostatic Pressure Capillary, MVT & Hydrostatic Pressure
Ravages of Moisture Amount of Moisture Extracted MVE of 20 lbs./1,000 sq. ft. (9,07 kg per 92,9 m )/ 24 hours 7 Days of Extracted Moisture 20lb MVER Roughly 16 gallons of water over a 7 day period over an area approximately 31’x31’
Solutions for Moisture Control Silicate Penetrating Sealers Topical Sealers Epoxy Coatings Cementitious Overlay Single system approach (adhesive acts as bonding agent and moisture control solution)
Penetrating Sealers Penetrating type reactive sealers are liquid applied treatments that chemically react with the concrete reducing the MVER. There are also products that are incorporated into the product at the time of pour. (mixed in the truck) These may be 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
Top Coat Sealers Typically used for lower MVER/PH conditions (approx. 8 lbs) May not require slab surface preparation depending upon surface condition of the slab Not typically recommended for open slab systems. May not be recommended for below grade slabs. Creates “non-porous” substrate
Epoxy Coatings There are single and multiple coat systems available. 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 sand broadcast
Dual Function Adhesive Systems New adhesive products designed to seal the slab and act as a bonding agent in one step. Water based acrylic adhesive Water based acrylic adhesive Moisture cure urethane adhesive Moisture cure urethane adhesive Typically designed for a maximum of 15lbs MVER and 90% RH May not be designed for certain types of floor covering May or may not be recommended for open slab systems or slabs with hydrostatic pressure.
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.
Slip Sheet Membranes “Free floats” accommodating minor cracks and joints. 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
Decisions Drivers and Pitfalls for Moisture Solution Selection Amount of remediation required (MVER and RH Levels) Available funds (Moisture Issues not typically expected) Incorrect system chosen for existing conditions / Lack of investigation. Incomplete system that does not include accommodations for cracks or joints. System requires “certification” prior to purchase and application / Warranties Liability/Support if failure occurs Incorrect application or slab preparation
Minor Defect Repairs Cement Based with Liquid Polymer Additives Dry Polymer Modified Cement based Dry Polymer Modified Gypsum based (residential and light commercial use) High hydrating, polymer and fiber reinforced cement based underlayments (skim coats) Typical Usages: From Feather egde to 1-1.5” Thickness in single application Use “exterior rated” patching compounds on slabs with moisture issues.
Large Area Repairs Self Leveling Underlayments Prep Prep Make sure the substrate has the proper CSP or profile to receive the levelerMake sure the substrate has the proper CSP or profile to receive the leveler Prime Prime Select the right primer for the substrateSelect the right primer for the substrate Pour Pour Follow all instructions on the packageFollow all instructions on the package Wait 3 days for floor covering installation Wait 3 days for floor covering installation
Deep Fill Repairs Screeds Typical fills up to 4” thick Typical fills up to 4” thick Cure time relatively quick but reset the clock in terms of flooring acceptance as much as 30 days Cure time relatively quick but reset the clock in terms of flooring acceptance as much as 30 days
Concrete Profiles for Self Leveling Underlayments
Crack Repair Mechanically prepare control and construction/expansion joints with a diamond crack-chasing/concrete- cutting blade. Overcut the joint width to obtain a sound, clean edge. Clean cracks or joints with oil free compressed air and/or vacuum with a dustless collection system to completely remove contaminants An Engineer or Consultant determines if a crack is ‘dormant’ or ‘active’ and which product to use
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