Concrete moisture testing is a precise technical procedure where protocol errors produce unreliable results — and unreliable results lead to flooring failures or unnecessary project delays. This field guide walks through the complete procedure for both ASTM F2170 (in-situ relative humidity) and ASTM F1869 (calcium chloride) testing, including site preparation requirements, test placement logic, and result documentation standards.

Pre-Testing Requirements: What Must Be True Before You Test

Both ASTM test methods specify conditions that must be met before testing begins. Testing outside these conditions produces results that don’t represent actual flooring installation conditions — and may invalidate warranty coverage.

• Concrete age: Minimum 28 days from pour. Younger concrete is still undergoing hydration reactions that produce elevated moisture readings unrelated to long-term vapor performance.
• HVAC operational: Permanent HVAC systems must be operating at conditions representative of building occupancy — typically 65–75°F and 40–60% RH — for a minimum of 48 hours before testing begins. Testing during construction heating or cooling, or before HVAC startup, produces non-representative results.
• Surface preparation complete: The concrete surface should be in the same condition as it will be at flooring installation. Any surface grinding, shot blasting, or adhesive removal planned before flooring must be completed before testing — these operations expose fresh concrete and restart the drying clock.
• No water intrusion events: Allow at least 72 hours after any water intrusion event (roof leak, flooding, excessive cleaning) before testing.

ASTM F2170 In-Situ RH Test: Step-by-Step Procedure

Step 1: Determine Test Locations

Mark test locations on a floor plan drawing. Minimum quantity: 3 probes for the first 1,000 sf, plus 1 per additional 1,000 sf. Prioritize locations at: areas suspected to have higher moisture (near exterior walls, over crawl spaces, at slab joints), areas with different concrete placement dates, and a representative sample of the general floor area. Document location coordinates on the floor plan — this becomes part of the test record.

Step 2: Drill Probe Holes

Drill holes at 40% of slab depth (± 5%). For a 4-inch slab, drill to 1.6 inches. Hole diameter must match the probe sleeve diameter — typically 3/4 inch. Use a rotary hammer drill with a carbide bit. Clean the hole thoroughly with a wire brush and blow out all dust and debris with compressed air. Dust contamination in the hole affects probe accuracy.

Step 3: Install Probe Sleeves and Seal

Insert the manufacturer-specified probe sleeve into the cleaned hole. Seal the hole opening around the sleeve with the provided plug or compatible sealant. The seal must prevent ambient air from reaching the probe during equilibration. Any air leak creates a pathway for ambient RH to influence the reading — a common source of test error in field conditions.

Step 4: Equilibration Period

Allow sealed probe locations to equilibrate for a minimum of 24 hours for slabs up to 4 inches thick; 72 hours for slabs over 4 inches or in conditions of high ambient RH. During equilibration, maintain stable HVAC conditions. Do not disturb or remove seals. The equilibration period is non-negotiable — readings taken before equilibration is complete will be artificially low and do not represent actual slab moisture conditions.

Step 5: Insert Calibrated Probes and Record Readings

Insert factory-calibrated or recently field-calibrated RH/temperature probes into the sleeves. Allow the probe to equilibrate within the sleeve for the time specified by the manufacturer (typically 1–10 minutes depending on probe type). Record: probe ID, calibration date, hole depth, slab thickness, RH%, temperature (°F), ambient RH, ambient temperature, and time of reading. Photograph each probe location with the reading displayed.

Step 6: Probe Calibration Verification

F2170 requires that probes be calibrated within 30 days of use using a NIST-traceable reference standard. Calibration records must accompany test reports. Field calibration check using a saturated salt solution (75.3% RH at 77°F for NaCl) is recommended at the start of each test day. Probes reading outside ±2% of the reference standard should be recalibrated or removed from service.

ASTM F1869 Calcium Chloride Test: Step-by-Step Procedure

Step 1: Surface Preparation

The concrete surface under each test dome must be clean and free of sealers, coatings, adhesive residue, and surface laitance. Lightly sweep and vacuum. Do not use water to clean — this introduces moisture and invalidates the test. Test areas must be at least 18 inches from walls, columns, or other surface features that affect surface evaporation.

Step 2: Condition the Test Area

Tape a plastic sheet over each test area for a minimum of 24 hours before test placement. This pre-conditions the surface to test-environment conditions and prevents initial moisture loss from open surface exposure affecting the test reading.

Step 3: Weigh Calcium Chloride Dishes and Place Domes

Record the pre-test weight of each sealed calcium chloride dish to 0.1 gram precision. Open the dish, place it on the conditioned surface, and immediately seal the dome over it. Record placement time. Do not disturb the dome during the test period.

Step 4: Test Period

Test period is 60–72 hours. During this time, maintain stable HVAC conditions at 65–75°F and 40–60% RH. Do not operate exhaust fans, open windows, or perform water-based operations in the test area. Record ambient temperature and RH at start and end of test period.

Step 5: Retrieve, Weigh, and Calculate

Remove the dome and immediately reseal the calcium chloride dish. Weigh within 10 minutes of removal. Calculate: MVER (lbs/1000 sf/24hr) = (weight gain in grams × 0.01) / test period in days. Record against the flooring manufacturer’s maximum MVER limit for the specified product.

Documentation: What the Test Report Must Include

A compliant concrete moisture test report for commercial flooring warranty purposes must include:

• Project name, address, and floor level tested
• Test method (ASTM F2170 or F1869) and edition year
• Date and time of test placement and reading
• Slab age at time of testing
• Ambient temperature and RH during testing
• HVAC status (permanent/temporary; setpoints)
• Test location diagram with dimensions to fixed references
• Individual results by location
• Probe calibration records (F2170) or pre/post weights (F1869)
• Technician name, certification number, and signature

IFTI provides documentation packages formatted to meet the requirements of major flooring and adhesive manufacturers, and maintains test records for five years from project completion.

Frequently Asked Questions

Can the GC’s superintendent perform moisture testing?

Technically, ASTM F2170 and F1869 do not require technician certification — only protocol compliance. However, for warranty purposes and dispute protection, testing performed by an independent certified third party is substantially more defensible than self-performed testing by a party with a schedule interest in the project proceeding. Most flooring manufacturers’ warranty language specifies “qualified independent testing.”

What if results vary significantly across the floor plate?

High variation across the floor plate is itself diagnostically significant. It typically indicates differential concrete placement (multiple pours with different ages), localized moisture sources (subslab leaks, utility penetrations), or areas of different slab thickness. High-variation situations warrant additional targeted testing before mitigation decisions are made — a mitigation system specified for the worst-case result may be over-specified for much of the floor area.