A resin floor is a thin layer bonded to your slab. If the bond fails, the floor fails, however good the resin was. Sika's prep guide calls surface preparation a critical factor in how the floor performs.
Who owns the prep
The Sika and Sherwin-Williams guides both say that handing over a sound, clean slab is the job of the owner or the concrete contractor unless the contract says otherwise. Ask each installer to write down which prep work is in the price.
Clean first, then profile
Contamination is anything that blocks a bond. Oil, grease, wax, old sealers, curing compounds. Both guides describe a simple check with distilled water and pH paper. Normal concrete reads 11 to 13. A reading of 10 or lower means more cleaning, and concrete that can't be cleaned has to be cut out and replaced. That matters in a kitchen that has run for years.
Profile is the roughness the resin grips. The International Concrete Repair Institute's guideline 310.2R grades it from CSP 1, nearly flat, to CSP 10, very rough. The number you need depends on the product. Sika's general guide calls for CSP 3 to 5, its MMA primer sheet says 3 to 6, and one of its MMA freezer systems says 4. Ask which number the data sheet for your system requires.
The profile is made by machine. Shot blasting throws steel shot at the slab and vacuums it back up. Diamond grinding does similar work and takes off old coatings. Acid etching is the one to turn down. Sika's MMA system sheet rules it out, and Stonhard says it is no longer recommended for commercial or industrial floors.
Repairs
Weak concrete comes out down to sound material and gets rebuilt. On Sika's MMA system sheet, cracks wider than 1/16 inch are opened up during prep, and the concrete around each drain is chipped down 1/2 to 3/4 inch and tapered back 3 to 6 inches. Joints are a separate decision. Ask how each one will be treated.
Moisture
Sherwin-Williams lists what excess moisture in a slab does. It can stop the resin curing properly, or push a non-breathing floor off the concrete. New concrete is normally left 28 days before coating, and the same guide warns that 28 days is not always long enough for the extra water to leave.
These are the test names to look for in a bid:
- ASTM F2170. Humidity probes set in holes drilled into the slab. Sherwin-Williams gives the depth as 40 percent of the slab's thickness, with three tests for the first 1,000 square feet, then one more per 1,000. It accepts 80 percent relative humidity or lower under non-breathing floors. Other products set their own limit.
- ASTM F1869. A dish of calcium chloride sealed under a dome on bare concrete for 60 to 72 hours. The result is pounds of water per 1,000 square feet per 24 hours. Sherwin-Williams and Sika's MMA primer sheet both set the ceiling at 3 pounds.
- ASTM F2659. A handheld electronic meter. Sika's MMA primer sheet allows a meter reading of 4 percent or less, and a system sheet says to call Sika's technical support above 5 percent.
- ASTM D4263. The plastic sheet method. It shows whether moisture is moving, not how much.
ASTM adds a caution: a result only describes the slab at the time it was taken. Sika wants the building at its normal temperature and humidity for at least 48 hours before testing.
If the numbers come back high, the usual answer is an extra layer under the floor that tolerates moisture. Sika's MMA primer sheet, for example, calls for a different base coat at least 1/8 inch thick when the meter reads over 4 percent. That adds cost and time.
Proof on the day
Sika's MMA sheets call for a bond test: a small patch of primer on the prepared floor. After 60 minutes it should be hard and should not scratch off with a knife. A tacky patch can mean something is still in the concrete. The sheets ask for one every 500 to 1,000 square feet. The slab also has to be at least 5°F above the dew point, so ask where the installer will measure slab temperature.
What to ask the installer
- Which prep method, and what CSP does the data sheet require?
- Which moisture test, at how many spots, and what is the limit for this product?
- What happens to the price and the schedule if the test fails?
- How will cracks, joints and drains be handled, and is that in the price?
Sources
- Sherwin-Williams, Concrete Surface Preparation guideline, Form G-1 (02/26)
- Sika, Sikafloor Surface Preparation Guide (2020)
- Sika, Sikafloor Pronto RB-1823 CQ system data sheet (2025)
- Sika, Sikafloor-13 Pronto MMA primer data sheet (2020)
- DeFelsko, ICRI Concrete Surface Profile chips (ICRI Guideline 310.2R)
- ASTM F2170-19a
- ASTM F1869-23
- Stonhard, How Your Flooring Installer Will Prepare Your Concrete Surface
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