A garage floor moisture test is useful only when the method, result and proposed coating are identified together. Ask for the test locations, date, units and manufacturer’s acceptance limit. A dry-looking floor or a handheld reading alone does not establish that a particular resin system is suitable.
Start with the test method, not the word “passed”
“We checked the moisture” leaves too much unanswered. A probe inside the slab, a calcium-chloride test on the surface and a handheld screening meter measure different things. Put the method beside the result before you compare it with a coating specification.
ASTM F2170: in-situ relative humidity testing describes internal relative-humidity testing. ASTM F1869: calcium-chloride moisture emission testing describes a method for measuring moisture vapor emission. The published summaries explain their scope; they are not a substitute for the full current test procedure. Ask the installer which edition and procedure the project requires.
| Result type | Record to request | Comparison to make |
|---|---|---|
| In-situ relative humidity | Probe locations, RH percentage, test conditions | The named system’s RH limit |
| Moisture vapor emission | Method, test duration, emission units | The named system’s emission limit |
| Handheld screening | Meter model, setting, locations | Whether the manufacturer accepts it for approval |
| Visual check | Water, staining, salts and recent weather | What further inspection is needed |
Match the result to the complete coating system
Ask for the proposed primer, any moisture-control layer, broadcast coat and topcoat by product name. Then ask which document defines the acceptance limit for that combination. A topcoat’s headline performance does not answer whether the primer belongs on your slab.
Keep each result in its original units. Do not accept an unexplained conversion between an RH percentage and an emission rate. If the proposal mentions more than one test, ask which result controls the decision and what happens if the tests point in different directions.
A useful reply is a document you can save: “This result is within this product’s stated limit under these conditions.” An unexplained “our product handles moisture” gives you nothing to compare.
A test record you can request by email
- Floor plan or photographs identifying each test location.
- Date, method and units, with the recorded result at each location.
- Whether old paint or another coating was present when testing began.
- Ambient and slab conditions required by the procedure.
- The selected system and the technical document used for acceptance.
- The proposed action if a result exceeds the system limit.
- Who retains the record and whether you receive a copy before installation.
This is a buyer’s record checklist. It is not a laboratory procedure. Leave probe placement, conditioning, calibration and timing to the person responsible for performing the specified test.
What a favorable result cannot promise
A result is evidence from the tested locations and conditions. It is not a permanent guarantee about every square foot. ASTM’s F2170 summary explicitly limits results to the time and locations tested. Tell the assessor about water that appears after rain, a leaking door, or a corner that stays damp; those observations deserve their own investigation.
For planning, separate three questions on the scope sheet: Is there liquid water entering the room? Is moisture within the slab compatible with the system? Could condensation interfere with installation? A proposal should explain which question its test addresses rather than use one favorable reading to answer all three.
If a result is outside the proposed limit
Pause the product decision. Ask for a revised system specification, additional investigation, or a decision to delay coating. Request the extra cost and the warranty implications in writing. A moisture-control product is a specified part of a system, not an automatic fix for an unexplained water source.
For a Michigan garage, tell the assessor whether the room is heated and whether wet vehicles regularly park inside. Include where water collects and how you remove it. These are observations about your property, not assumptions that every Detroit slab behaves alike.
Bring the result into the quote
Use the same-scope cost worksheet to separate testing and any added moisture treatment. Read the warranty checklist before treating moisture protection as included. For below-grade rooms, start with the basement coating planning guide.
Describe your floor and moisture history if you want to discuss a project. Photos help locate the question; they do not replace a test result.
References behind this guide
- ASTM F2170: in-situ relative humidity testing
- ASTM F1869: calcium-chloride moisture emission testing
- Sikafloor 510 LPL product data sheet, February 2025
Technical limits apply to the named product or test. Confirm the current requirements for your proposed system.
