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When testing a concrete slab that is drying from only one side (e.g., slab on grade with vapor retarder beneath), ASTM F2170 requires that the relative humidity probe be inserted at what depth as a percentage of the slab thickness?

A
B
C
D
to track
2026 Statistics

Key Facts: ICRI CSMT Exam

40% / 20%

F2170 Probe Depth

ASTM F2170 (one/two-sided)

72 hours

F2170 Equilibration

ASTM F2170

75% RH

Common F2170 Threshold

Flooring industry

3 lbs

Common F1869 MVER Limit

Per 1,000 sq ft/24 hr

60–72 hr

F1869 Test Duration

ASTM F1869

pH ≤ 9

F710 Surface pH Limit

ASTM F710

The ICRI Certified Concrete Slab Moisture Testing Technician (CSMT) credential certifies professionals who perform moisture testing on concrete slabs before flooring installation. The exam covers the four primary ASTM test methods — F2170 in-situ RH probes (40% depth for one-sided drying, 20% for two-sided, 72-hour equilibration, 75% RH common threshold), F1869 calcium chloride (60–72 hr duration, 3 lbs/1,000 sq ft/24 hr common threshold), F2659 electrical impedance (indicative/screening only), and F710 surface preparation (pH ≤ 9) — plus vapor retarder classification (ASTM E1745), slab drying fundamentals (28 days/inch rule of thumb), and chain-of-custody documentation standards.

Sample ICRI CSMT Practice Questions

Try these sample questions to test your ICRI CSMT exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1When testing a concrete slab that is drying from only one side (e.g., slab on grade with vapor retarder beneath), ASTM F2170 requires that the relative humidity probe be inserted at what depth as a percentage of the slab thickness?
A.40% of the slab thickness
B.20% of the slab thickness
C.50% of the slab thickness
D.60% of the slab thickness
Explanation: ASTM F2170 specifies that for slabs drying from one side only (e.g., slabs on grade with a vapor retarder underneath), the relative humidity sensor must be placed at 40% of the slab thickness from the drying surface. This depth represents where the equilibrium moisture gradient stabilizes and is the most predictive location for long-term moisture conditions at the floor surface.
2ASTM F2170 requires that relative humidity probes equilibrate in their installed holes for a minimum of how many hours before a reading is recorded?
A.72 hours
B.24 hours
C.48 hours
D.12 hours
Explanation: ASTM F2170 mandates a minimum 72-hour equilibration period after the probe is installed in the drilled hole, with the hole sealed. This allows the microenvironment within the hole to reach moisture equilibrium with the surrounding concrete matrix. Readings taken before 72 hours are considered unreliable and non-compliant.
3Many flooring adhesive manufacturers and flooring industry standards cite 75% relative humidity as the maximum allowable in-situ RH level for installing resilient flooring over concrete. If a slab tests at 78% RH, the correct course of action is to:
A.Delay installation and allow additional drying time or apply a vapor mitigation system before installing flooring
B.Proceed with installation since 78% is close enough to the 75% threshold
C.Increase HVAC airflow over the slab surface for 24 hours, then immediately re-test and install
D.Apply flooring adhesive and install immediately because adhesive tolerances absorb minor variance
Explanation: A slab reading 78% RH exceeds the commonly cited 75% RH threshold specified by flooring manufacturers and referenced in ASTM F2170 guidelines. Proceeding would void the flooring manufacturer's warranty and risk adhesive failure, bubbling, or mold growth. The correct action is to allow additional drying, use mechanical dehumidification, or install an appropriate vapor mitigation system (e.g., topical sealer rated for the measured RH level) before flooring installation.
4ASTM F1869 is the standard test method for measuring moisture vapor emission rate (MVER) using anhydrous calcium chloride. What is the standard test duration for the ASTM F1869 calcium chloride test?
A.60 to 72 hours
B.24 hours
C.48 hours
D.7 days
Explanation: ASTM F1869 specifies that the calcium chloride dish must remain sealed over the slab surface for 60 to 72 hours. The amount of moisture absorbed by the anhydrous calcium chloride during this period is weighed, and MVER is calculated in pounds of moisture per 1,000 square feet per 24 hours. The 60–72 hour window provides a standardized and reproducible measurement period.
5According to ASTM F1869, what is the commonly cited maximum moisture vapor emission rate (MVER) threshold for most standard resilient flooring adhesive installations?
A.3 pounds per 1,000 square feet per 24 hours
B.5 pounds per 1,000 square feet per 24 hours
C.8 pounds per 1,000 square feet per 24 hours
D.1 pound per 1,000 square feet per 24 hours
Explanation: The widely accepted MVER threshold for standard resilient flooring and adhesive installations is 3 lbs/1,000 sq ft/24 hr, as referenced in ASTM F1869 and specified by many flooring manufacturers. Exceeding this threshold is associated with adhesive bond failure, bubbling, and flooring delamination. Some specialty adhesives or moisture-tolerant systems allow higher limits, but 3 lbs is the baseline standard.
6Before placing the calcium chloride dish for an ASTM F1869 test, the slab surface must be prepared. Which of the following correctly describes the required surface preparation?
A.Remove all surface contaminants, coatings, and adhesive residue by mechanical means; the surface must be bare concrete
B.Apply a concrete primer and allow it to cure for 24 hours before placing the dish
C.Wet the slab lightly with water and allow it to surface-dry for 30 minutes before placing the dish
D.Sweep the area clean and place the dish directly over any existing floor coating
Explanation: ASTM F1869 requires that the test area be free of all coatings, adhesives, curing compounds, and contaminants that could interfere with the natural moisture vapor transmission from the slab. The surface must be bare, clean concrete. If coatings are present, they must be removed mechanically (e.g., grinding, scarifying) before testing to obtain an accurate emission rate.
7ASTM F1869 specifies that the test area must be conditioned at a minimum temperature and relative humidity for a minimum time before testing. What are those requirements?
A.Minimum 65°F and 40% to 60% RH for at least 48 hours before testing
B.Minimum 60°F with no humidity specification for 24 hours before testing
C.Minimum 70°F and 50% RH for at least 72 hours before testing
D.Any temperature above freezing for 12 hours before testing
Explanation: ASTM F1869 requires that the test environment be conditioned at a minimum temperature of 65°F (18°C) and a relative humidity between 40% and 60% for at least 48 hours before and during the test. This conditioning period ensures that the test represents service conditions and that the slab moisture state is stable before measurement begins.
8ASTM F2659 describes a method for measuring concrete moisture using an electrical impedance meter. Compared to ASTM F1869 and ASTM F2170, how is ASTM F2659 best characterized?
A.As an indicative (screening) test only — results cannot be used as the sole basis for flooring installation decisions
B.As a primary test method with results that supersede ASTM F1869 calcium chloride test results
C.As equivalent to ASTM F2170 for measuring in-situ relative humidity throughout the slab depth
D.As a destructive test method requiring core sampling
Explanation: ASTM F2659 (Standard Guide for Preliminary Evaluation of Comparative Moisture Condition of Concrete, Gypsum Cement, and Other Floor Slabs Using a Non-Destructive Electronic Moisture Meter) explicitly categorizes the electrical impedance test as a preliminary, indicative screening method. Results can identify areas needing further investigation but cannot stand alone as the basis for flooring installation decisions; ASTM F2170 or F1869 must be used for definitive measurements.
9A concrete slab is 6 inches thick and is suspended above grade, exposed to air both above and below (drying from two sides). At what depth should the ASTM F2170 RH probe be installed?
A.1.2 inches (20% of 6-inch slab thickness)
B.2.4 inches (40% of 6-inch slab thickness)
C.3 inches (50% of 6-inch slab thickness)
D.4.8 inches (80% of 6-inch slab thickness)
Explanation: For a slab drying from two sides, ASTM F2170 specifies probe insertion at 20% of the slab thickness from either drying surface. For a 6-inch slab: 6 × 0.20 = 1.2 inches. Two-sided drying creates a symmetric moisture gradient, so the 20% depth from the top (or bottom) captures the equilibrium moisture condition for that drying scenario.
10ASTM F710 — the standard practice for preparing concrete floors to receive resilient flooring — requires that the concrete surface pH not exceed which value?
A.pH 9
B.pH 7
C.pH 11
D.pH 12
Explanation: ASTM F710 specifies that the concrete surface pH should not exceed 9 for resilient flooring installation. High pH (>9) can attack adhesive bonds and cause adhesive failure. Surface pH is measured by wetting a small area with distilled or deionized water and testing with pH paper or a calibrated meter after one minute of contact.

About the ICRI CSMT Exam

Professional certification for technicians who perform concrete slab moisture testing prior to flooring installation. Covers ASTM F2170 in-situ relative humidity testing, ASTM F1869 calcium chloride testing, ASTM F2659 electrical impedance testing, ASTM F710 surface preparation, vapor retarder requirements, and chain-of-custody documentation.

Questions

100 scored questions

Time Limit

2 hours

Passing Score

70%

Exam Fee

Contact ICRI (ICRI (International Concrete Repair Institute))

ICRI CSMT Exam Content Outline

~35%

ASTM F2170 In-Situ RH Testing

Probe depth (40%/20%), 72-hr equilibration, hole preparation, probe calibration, test conditions

~25%

ASTM F1869 Calcium Chloride Testing

Test duration, MVER calculation, surface prep, kit placement, anhydrous calcium chloride

~15%

Slab Drying & Moisture Fundamentals

28-day/inch rule, w/c ratio, curing compounds, lightweight concrete, efflorescence

~10%

Vapor Retarders & Sub-Slab Conditions

ASTM E1745 classes, permeance, capillary rise, sub-slab moisture sources

~8%

ASTM F710 Surface Preparation

pH testing (≤9), laitance removal, surface contaminants, mechanical preparation, F-numbers

~7%

Chain-of-Custody, Reporting & Program Overview

Test reports, documentation, ASTM F2659 screening, ICRI CSMT credential requirements

How to Pass the ICRI CSMT Exam

What You Need to Know

  • Passing score: 70%
  • Exam length: 100 questions
  • Time limit: 2 hours
  • Exam fee: Contact ICRI

Keys to Passing

  • Complete 500+ practice questions
  • Score 80%+ consistently before scheduling
  • Focus on highest-weighted sections
  • Use our AI tutor for tough concepts

ICRI CSMT Study Tips from Top Performers

1Memorize the F2170 probe depth rule: 40% depth for one-sided drying (slab on grade with vapor retarder), 20% for two-sided drying (suspended slab) — calculate from the drying surface
2Know the 72-hour equilibration minimum for F2170 probes — readings before 72 hours underestimate true slab RH because the hole has not fully equilibrated
3The 75% RH (F2170) and 3 lbs/1,000 sq ft/24 hr (F1869) are common thresholds — but always check the specific flooring manufacturer's installation data sheet
4F1869 calcium chloride: test for 60–72 hours, minimum 3 kits per 1,000 sq ft (first area) + 1 per additional 1,000 sq ft
5ASTM F2659 electrical impedance = screening/indicative only — never the definitive installation decision test
6ASTM F710 surface pH maximum is 9; test with distilled water, not tap water
7The 28-days/inch rule is a planning estimate, not a guarantee — actual testing (F2170 or F1869) is always required for installation decisions
8Chain-of-custody documentation must include: probe ID and calibration date, drilling date, reading date/time, probe depth, slab thickness, ambient conditions, and a floor plan showing probe locations

Frequently Asked Questions

What is the ICRI CSMT certification?

The ICRI Certified Concrete Slab Moisture Testing Technician (CSMT) is a professional credential administered by the International Concrete Repair Institute (ICRI) that certifies technicians who perform concrete slab moisture testing prior to flooring installation. It demonstrates verified knowledge of ASTM F2170, F1869, F2659, F710, and related standards for moisture testing and documentation.

What is the most important number to know for the ASTM F2170 test?

Two key numbers: (1) Probe depth — 40% of slab thickness for slabs drying from one side (slab on grade with vapor retarder), 20% for slabs drying from two sides (suspended slabs). (2) Equilibration time — minimum 72 hours sealed in the hole before taking a valid reading. The common flooring threshold is 75% RH, but always check the flooring manufacturer's specification.

What is the MVER threshold for ASTM F1869 calcium chloride testing?

The commonly cited threshold for most resilient flooring adhesive installations is 3 lbs per 1,000 square feet per 24 hours. The test itself runs for 60–72 hours. A minimum of 3 kits are required for the first 1,000 sq ft, plus 1 additional kit per additional 1,000 sq ft of slab area.

What is ASTM F2659 used for?

ASTM F2659 (electrical impedance testing) is an indicative (screening) test only. It cannot be used as the sole basis for flooring installation decisions. It is appropriate as a preliminary screening tool to identify areas of higher moisture concentration on large slabs, helping to strategically place ASTM F2170 probes or F1869 dishes for definitive testing.

What pH limit does ASTM F710 require for concrete floors?

ASTM F710 requires that the concrete surface pH not exceed 9. Surface pH is tested by moistening the prepared concrete surface with distilled or deionized water, waiting one minute, then measuring with calibrated pH strips or a pH meter. High pH (above 9) can cause saponification (chemical breakdown) of flooring adhesive.

How long does it take for a concrete slab to dry enough for flooring?

The industry rule of thumb is approximately 28 days per inch of slab thickness for normal-weight concrete under standard conditions (65–77°F, 40–60% RH, HVAC operating). However, this is only an estimate — actual drying depends on w/c ratio, curing method, HVAC operation, and whether a vapor retarder is present. Lightweight concrete takes significantly longer. Always verify with ASTM F2170 or F1869 testing before installation.