Substrate Preparation and Surface Conditions
What to know
Grout bonds only to a clean, sound, properly roughened, and moisture-conditioned substrate. Candidates must know the sequence: remove laitance, oil, dust, curing compound, and loose material; achieve a surface profile (typically CSP 3–5 for cementitious grout); and pre-condition the substrate-usually saturated-surface-dry (SSD) for cementitious grout, but dry and clean for most epoxy grouts.
Traps in questions
- Confusing SSD for cementitious grout with the dry requirement for epoxy. Wet substrate can blush or weaken epoxy bonds.
- Overlooking curing compound residue, which blocks bond even after visible cleaning.
- Ignoring substrate temperature and dew point. If substrate temperature is within about 5°F (3°C) of dew point, condensation risk is high.
- Assuming roughening alone is enough; dust and laitance must be removed after mechanical prep.
Worked example / rule of thumb
Dew point check: if air is 70°F at 60% RH, dew point is about 55°F. If the slab reads 58°F, you are within 3°F of dew point-postpone grouting or control conditions. Rule of thumb: keep substrate at least 5°F above dew point before and during placement.
Key concepts to name
Laitance, CSP profile, SSD, bond breaker, curing compound, dew point, substrate temperature, moisture vapor emission, and surface preparation methods (shot blasting, scarifying, grinding, acid etching).