SW-04 · Subfloors & MoistureFresh concrete is strongly alkaline, and high alkalinity at the surface can stop a flooring adhesive from bonding.1 ASTM F710 says every concrete floor should be tested for pH before resilient flooring goes down.2 The acceptable range is set by the flooring and adhesive manufacturers, and published windows run from as low as 5 to as high as 10.3 4
Moisture and pH are usually tested on the same visit, and for good reason. Water moving up through a slab carries alkaline salts with it, and those salts end up where the flooring meets the concrete. A slab can pass its moisture test and still have a surface that attacks the adhesive. That is why the standards treat pH as its own check, not as a footnote to moisture.
Why alkalinity matters
Concrete is alkaline by nature. HORIBA makes pH meters used for this test. It notes that fresh concrete is usually very alkaline, above pH 11. When alkalinity in a subfloor is high, it can stop the floor covering adhesive from bonding properly.1 Some adhesives soften or re-emulsify. Others lose grip at the interface while looking intact from above. Either way the failure shows up later, as lifting edges, bubbles or a floor that moves under rolling loads.
The visible sign of alkaline salts on a slab is efflorescence, the white powder or crystal growth that appears where water has evaporated and left minerals behind. It is a warning, not a measurement. A slab with no visible salts can still read high, which is why the surface gets tested.
What the standard requires
ASTM F710 is the practice for preparing concrete floors to receive resilient flooring. It states that all concrete floors should be tested for pH before installation, alongside moisture tests on every slab regardless of age or grade level.2 Elite Flooring's installation guide points to the same standard as the method for determining a slab's pH.4 For a commercial specification, citing F710 makes pH testing part of the substrate acceptance rather than an optional extra.
How the surface is tested
A pH test reads the surface the adhesive will touch, so the surface has to be representative. Laitance, curing compound or old residue gives a reading of the contaminant, not the slab. The method HORIBA describes is simple: put several drops of distilled or de-ionized water on the prepared surface, leave them for 60 seconds, then draw the water off with a pipette and measure it.1 Test strips and pens work on the same principle. Whatever the tool, test at several locations, especially where moisture readings were highest, and record each reading with its location.
Testing elsewhere in the world shows how much the limit depends on the system. Australia's resilient flooring installation standard, AS 1884, states that the pH of the concrete surface should be between 9 and 10 before flooring can be installed.1 North American manufacturers set their own ranges, and they are not the same.
Published ranges compared
These are the pH requirements stated in five installation documents for vinyl flooring. Each applies to its own products and their approved adhesives.
| Document | Concrete pH range |
|---|---|
| EverStep, click-lock LVP | Between 5.0 and 9.03 |
| EverStep, glue-down LVP | Between 7 and 95 |
| Timeless Designs, click floating vinyl | Between 7 and 96 |
| National Flooring Products, Architect's Choice | Between 5 and 97 |
| Elite Flooring, Välinge lock | Between 7 and 10, determined by ASTM F7104 |
The upper limits matter most, because high readings are the common problem on newer slabs. A reading that passes for one product can fail for another, so check the result against the flooring and adhesive actually specified. Where the flooring is glued, the adhesive manufacturer's own limit applies as well, and it may be the stricter of the two.
When a slab reads high
A high reading is a decision, like a failed moisture test. The usual options are three. Remove a contaminated surface layer mechanically and retest. Use a primer or underlayment system rated for the measured alkalinity. Or choose an adhesive and flooring combination whose published limits the slab meets. Moisture and pH often travel together. A high pH reading is a reason to look again at the moisture results, and at whether the slab has a working vapor retarder.
Avoid quick fixes that are not in any manufacturer's documents. Washing a slab with acid or applying an unapproved sealer changes the surface for the test without changing the slab, and the next round of moisture will bring the salts back. On a commercial job, any treatment should be one the flooring or adhesive manufacturer names, with its limits in writing.
Recording the result
Record pH the same way as moisture: method, date, conditions, each location on a plan, each reading, and the limit it was compared against. Keep the record with the moisture tests and the closeout documents. If an adhesive fails, the first questions will be about moisture and alkalinity, and a documented reading inside the published range is the strongest answer an installer can give.
Sources
- HORIBA, “pH of Cement for Floor Installation Testing - HORIBA”. horiba.com/usa/water-quality/applications/manufacturing/ph-of-cement-for
- ASTM International, “F710 Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring”. store.astm.org/f0710-22.html
- EverStep Flooring, “LVP Click Lock Installation Guidelines”. everstepflooring.com/lvp-click-installation-guidelines/
- Elite Flooring, “Välinge Installation Guide (Woodlands)”. eliteflooringusa.com/links/install-instructions/Elite-Installation-Guide
- EverStep Flooring, “LVP Glue Down Installation Guidelines”. everstepflooring.com/technical/lvp-glue-down-installation-instructions/
- Timeless Designs, “Click Floating Luxury Vinyl Installation Instructions”. timelessdesignsflooring.com/wp-content/uploads/2023/05/TD-Rigid-Core-Ins
- NFP, “Architect’s Choice LVP Installation Guide”. my-nfp.com/resource/architects-choice-lvp-installation-guide
General information for the flooring trade. This article was drafted with AI assistance and checked against the sources listed above; the manufacturer's current instructions and the project specification govern any real job. If something here is wrong or out of date, tell us.
