ACI Decorative Concrete & Stamping 2 — Questions and Answers
Question 1: What is the primary purpose of a release agent applied before stamping concrete?
- To accelerate curing of the slab
- To prevent stamps from sticking to the concrete surface (Correct answer)
- To increase the compressive strength of the mix
- To add air entrainment to the concrete
Correct answer: To prevent stamps from sticking to the concrete surface
Release agents create a barrier between the stamp tool and fresh concrete so the tool lifts cleanly without tearing the surface texture.
Question 2: Which tool is used to create a grout line effect between stamped pattern sections?
- Bull float
- Texture roller
- Grout groover or seamless touch-up skin (Correct answer)
- Fresno trowel
Correct answer: Grout groover or seamless touch-up skin
A grout groover or seamless touch-up skin is used to hand-cut or blend joint lines between stamp patterns to simulate grout joints.
Question 3: What effect does using too much powdered color release agent have on a stamped concrete surface?
- It produces a uniform, solid-color finish
- It can cause excessive surface dusting and color blotchiness (Correct answer)
- It makes the concrete cure faster
- It increases the bond strength of a sealer
Correct answer: It can cause excessive surface dusting and color blotchiness
Excess powdered release agent that is not fully removed before sealing can cause dusting, peeling, and uneven color in the finished surface.
Question 4: When stamping a border pattern around a field pattern, which area should generally be stamped first?
- The field (interior) pattern
- The border pattern (Correct answer)
- Either area — order does not matter
- Always start at the lowest elevation
Correct answer: The border pattern
The border is typically stamped first so that the field pattern can be adjusted and trimmed neatly to meet the established border edge.
Question 5: What is the recommended minimum number of stamp mats used at one time when stamping a large decorative slab?
- One
- Two
- Three to four (Correct answer)
- Ten or more
Correct answer: Three to four
Using three to four mats allows the finisher to rotate tools — one is being positioned, one is being pressed, and one is being lifted — maintaining continuous working progress.
Question 6: Which type of concrete sealer is most commonly used over stamped concrete for outdoor applications?
- Penetrating silane sealer
- Solvent-based or water-based acrylic sealer (Correct answer)
- Epoxy coating
- Latex paint
Correct answer: Solvent-based or water-based acrylic sealer
Acrylic sealers (solvent- or water-based) are the industry standard for stamped concrete because they enhance color, provide a sheen, and offer good weather resistance.
Question 7: What is 'ghosting' in stamped concrete?
- A translucent finish technique using diluted acid stain
- Faint impressions of stamp patterns visible through a sealer (Correct answer)
- A two-tone color effect created with two release agents
- The process of reapplying color hardener after sealing
Correct answer: Faint impressions of stamp patterns visible through a sealer
Ghosting occurs when stamp tool impressions show through successive sealer coats because the sealer pooled in low-relief areas, creating a visible pattern outline.
ACI Decorative Concrete & Stamping 2
What is the primary purpose of a release agent applied before stamping concrete?