Concrete moisture testing is how a contractor determines whether a slab is dry enough, and stable enough, to receive a coating or resinous flooring system without risking adhesion failure. Several distinct test methods exist, each reporting a different kind of result, so understanding which test answers which question is central to planning a coating project. This guide covers the main moisture and alkalinity test methods used before coating work, how test placement and building conditions affect what the results mean, and how to read a test report against the limits published on a coating manufacturer's data sheet. Choosing a mitigation system once a slab tests too wet, and repairing a floor that has already failed from moisture, are covered in separate guides linked below.
All concrete subfloors emit some moisture in vapor form (ASTM F1869), and a slab can still hold excess moisture after a typical 28-day cure, so a slab that looks dry may not be. Moisture testing exists because flooring manufacturers require it before a coating is installed, and because the consequences of skipping it show up after the floor is already in service.
ASTM F2170, the standard covering relative humidity testing with in-situ probes, notes in its significance section that excess slab moisture after a floor covering is installed can cause debonding, peaking, deterioration of the finish, and microbial growth. ASTM F1869, the calcium chloride vapor emission test, similarly exists to give a value indicating whether a floor is acceptable to receive a resilient floor covering, while noting that the result only reflects conditions at the time of the test.
Sherwin-Williams notes that a 28-day cure is commonly treated as a standard timeframe for concrete, but that this interval is not always sufficient for excess moisture to leave a slab, which is why moisture testing is recommended rather than relying on age alone.
Ask contractors on the Colorado Concrete Surface Preparation contractor hub whether moisture testing is in their scope, and coating-specific contractors through the Colorado Commercial Epoxy Flooring contractor hub.
ASTM F2170 covers the quantitative determination of percent relative humidity inside a concrete slab using probes inserted into drilled holes, for field or laboratory testing. The method reports a percent relative humidity figure that reflects only the time of the test and the locations tested.
Sherwin-Williams, describing how the test is deployed, says probe holes are drilled to a depth equal to 40 percent of the slab thickness; Tnemec describes the same 40 percent figure, while DeFelsko notes that a slab drying from both sides may be tested at 20 percent of thickness instead. Sherwin-Williams describes three tests in the first 1,000 sq ft plus one per additional 1,000 sq ft; DeFelsko likewise states a three-probe minimum for the first 1,000 sq ft. Project specifications can require more.
The public ASTM F2170 text states no pass/fail number. Any RH limit a project uses comes from the coating or adhesive manufacturer, not from the standard. For example:
| Product (manufacturer) | RH limit (ASTM F2170) |
|---|---|
| Series 201 Epoxoprime primer (Tnemec) | 80% or lower |
| Non-permeable resinous systems, general guideline (Sherwin-Williams Form G-1) | 80% or lower |
| Resuflor MPE epoxy coating (Sherwin-Williams) | Below 75% |
| Sikafloor-264 epoxy, project-specific requirement (Sika) | 85% or lower |
These figures are product-specific and are not interchangeable between manufacturers or between products from the same manufacturer. ASTM F2170 itself states that results indicate the slab's condition only at the time of the test and only in the locations tested; Tnemec's data sheet adds that testing cannot guarantee against future moisture problems.
ASTM F1869 covers the quantitative measurement of moisture vapor emission from bare concrete floors, expressed as pounds of moisture over a 1,000 sq ft area during a 24-hour period. It is performed by sealing a dish of anhydrous calcium chloride under a dome on the slab surface.
Sherwin-Williams, describing the method, says it is conducted over raw exposed concrete that has been exposed to the environment for at least 24 hours, with the calcium chloride dish sealed under the dome for 60 to 72 hours.
ASTM F1869 states plainly that the test shall not be used on gypsum concrete or floors containing lightweight aggregate, and shall not be used over coatings, reactive penetrants, or patching and leveling compounds — it is a bare-concrete test only. The standard also states that all concrete subfloors emit some moisture in vapor form, and that the result reflects the floor's condition only at the time of the test.
As with RH testing, the pass/fail figure comes from the coating manufacturer, not from ASTM. Tnemec's Series 201 data sheet sets 3 lb per 1,000 sq ft per 24 hours for that primer, and Sherwin-Williams Form G-1 calls 3 lb a commonly accepted value for polymer coatings; moisture-mitigating primers publish much higher limits.
ASTM D4263 is a practice for indicating the presence of capillary moisture in concrete by the plastic sheet method. It is a qualitative method: the public scope states that it indicates the presence of moisture rather than producing a percentage, an emission rate, or a pass/fail number, so it should not be treated as a substitute for RH probe or calcium chloride results.
Some manufacturers also specify a direct surface-moisture meter reading as an additional, separate check. Sika's Sikafloor-264 data sheet requires 4% by mass or less measured with a Tramex-type meter on the mechanically prepared surface.
ASTM F710's public abstract says all concrete slabs should be tested for moisture and all concrete floors for pH before resilient flooring is installed; it is written for resilient flooring, and coatings are not specifically within its scope. ASTM F710 does not specifically cover coatings; its procedures "may be useful" for them. Coating pH requirements come from the coating manufacturer's data sheet. ASTM F710, written for resilient flooring, also says a permanent moisture vapor retarder is required under on- or below-grade floors.
A written scope should specify whether pH testing is included and how a result outside the coating manufacturer's stated range will be handled, since this is a separate question from the moisture readings discussed above.
Where and when a test is run affects what the number means. Sherwin-Williams states that moisture vapor test values are not useful for predicting problem areas unless tests are conducted in the environment the structure will actually be used in, with the same air temperature and humidity expected during its service life.
Tnemec recommends that concrete moisture tests be conducted only after the building's HVAC system has operated for at least 48 hours, and DeFelsko similarly advises that the slab and ambient conditions be held at service conditions for a minimum of 48 hours before testing begins. Confirm the planned conditioning period and HVAC status with the contractor in writing before testing begins.
ASTM F2170 states results reflect the slab only at the time and in the locations tested, and F1869 states its result reflects the floor only at the time of the test, so a single reading does not characterize the whole floor.
The public text of ASTM F2170 and F1869 gives no pass/fail number; the acceptance limit is normally taken from the flooring or coating manufacturer's data sheet for the specific product. The table in the RH section above illustrates how widely these figures vary even among coatings from the same manufacturer, and Tnemec's own educational material describes a "general rule" of 3 lb vapor transmission or 75 to 80 percent RH for conventional primers, while specialty primers and toppings are rated to tolerate moisture vapor transmission up to 20 lb and relative humidity up to 99 percent.
Before work proceeds, ask for the specific coating product's current data sheet, confirm which test method its limit is written against (F2170, F1869, or a surface meter reading), and get the comparison between the test result and that limit in writing. If a slab tests outside a product's limit, that moves the project into moisture mitigation planning, covered in the Moisture Mitigation for Colorado Slabs guide, rather than into the testing process itself. Budgeting for testing and surface preparation together is covered in the Concrete Surface Preparation Cost in Colorado guide, with epoxy-specific costs in the Commercial Epoxy Flooring Cost in Colorado guide, or estimated directly with the FloorSpec cost calculator.
That depends on which test the specified coating or adhesive manufacturer's data sheet calls for. ASTM F2170 measures relative humidity inside the slab using in-situ probes, while ASTM F1869 measures the rate of moisture vapor emitted from a bare concrete surface over a 24-hour period. Some coating data sheets cite F2170 RH limits, others cite F1869 MVER limits (Tnemec 201 lists both); the data sheet names which. F1869 applies only to bare concrete, not over coatings, reactive penetrants, or patching/leveling compounds.
No. ASTM D4263 is a qualitative practice that indicates whether capillary moisture is present but produces no percentage, emission rate, or pass/fail value. It indicates only the presence of capillary moisture and gives no number; the quantitative results manufacturers request come from F2170, F1869, or, for some Sika products, a surface moisture meter.
No. ASTM F2170 states that its results indicate the slab's condition only at the time of the test and only in the specific locations tested, and Tnemec's product data notes that testing cannot guarantee against future moisture problems. A passing result describes conditions on the day of the test, not a permanent condition of the slab.
Because the limit is set by each manufacturer for each specific product, not by the ASTM test methods themselves. For example, Sherwin-Williams' Resuflor MPE epoxy requires RH below 75%, while its Form G-1 guideline for non-permeable systems generally cites 80%. Always confirm the limit on the current data sheet for the exact product specified.
No. Sherwin-Williams notes that 28 days is commonly treated as a standard cure period for concrete but states this is not always enough time for excess moisture to leave a slab, which is why moisture testing is recommended regardless of the slab's age.
How moisture mitigation systems work on slab-on-grade concrete, when a coating project needs one, and what to put in the written scope.
What concrete surface preparation costs per square foot in Colorado, how it scales by market, and why prep scope often decides the final coating price.
What to do when a coated floor shows moisture-related failure: how to diagnose blisters, delamination, and pinholes, and the repair paths that work.
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