Concrete

Concrete pH and Alkalinity Testing

How the ASTM F710 surface pH test works, why the limit comes from your adhesive, and why you test after surface prep, not before.

Updated · 2 min read

Fresh concrete is highly alkaline, and high alkalinity attacks many flooring adhesives. A surface pH test takes a few minutes and tells you whether the slab is inside the limit your adhesive allows. The limit comes from the adhesive, not from a single industry number.

Why concrete pH matters

The reading depends on the cement and how much of the surface has carbonated.

  • Concrete made with Type II cement reads higher than 12.5, and high-alkali cement reads higher than 13.[1]
  • Carbonation brings the very top of the slab down to roughly pH 9.[1]
  • Grinding or blasting removes that carbonated layer. In one published comparison, sanded concrete powder read 12.5 while the F710 surface method read 9.5 on the same slab.[1] Test after prep, not before.

The ASTM F710 test, step by step

The F710 method is quick and needs only distilled water and pH paper or a pH pen.

  1. Finish surface prep first. Grinding, shot blasting or scraping changes the reading.
  2. Clean the test spot of dust and debris.
  3. Put a few drops of distilled or deionized water on the clean concrete to make a puddle about 1" (25 mm) across.[1]
  4. Let it sit for 60 seconds, give or take 5, then dip the pH paper into the water.[1]
  5. Compare to the color chart right away and record the number, location and date.
  6. Test in several locations. Many specs place pH tests next to the moisture test sites so both records line up.

What number is acceptable

The adhesive's instructions set the limit, and the range varies a lot between products.

Product Allowed surface pH
AHF/Armstrong default, unless the adhesive says otherwise 9 or less[2]
Armstrong S-995 8 to 10 on or above grade; 9 below grade[3]
Armstrong S-1000 5 to 14[3]
Mapei Ultrabond ECO 379 Do not install at 12 or higher[4]

A common claim online is that F710 requires pH 9 or less. Sources disagree on whether that number is in the standard or comes from manufacturers, so always go by the adhesive's own data sheet.

If the reading is high

A high number doesn't always mean tearing anything out, but it does mean checking with the manufacturer before you glue.

  • Check whether a different adhesive in the same system is rated for your number.
  • Ask the flooring or adhesive maker which primer, patch or mitigation system they approve for high-pH slabs, and get it in writing.
  • High pH often shows up with high moisture. Run moisture tests at the same time.

Common mistakes

Most bad pH readings come from testing at the wrong time or with the wrong water.

  • Testing before grinding. The carbonated skin reads low; the fresh surface you'll glue to reads higher.
  • Using tap water. The method calls for distilled or deionized water.
  • Reading too early or too late. Stick to the 60-second wait.
  • Assuming one limit fits every adhesive. Two adhesives from the same maker can have very different ranges.

Tools and prep products we carry

These cover testing and the prep work that usually comes next.

References

  1. ICRI Concrete Repair Bulletin: surface pH and ASTM F710 test method
  2. AHF/Armstrong: Dry-back LVT installation instructions
  3. AHF/Armstrong: Commercial sheet installation instructions
  4. Mapei: Ultrabond ECO 379 technical data sheet

Linked PDF documents are archived copies saved by PreFloor Tools so they stay available if the publisher moves or removes them. Check the publisher's website for the latest revision.

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