ACI Color & Texture Finishing 3 — Questions and Answers
Question 1: When applying a surface retarder to achieve an exposed aggregate finish, how should the retarder be applied?
- Sprayed onto the subbase before concrete placement
- Applied evenly to the fresh concrete surface immediately after screeding and floating (Correct answer)
- Brushed onto the forms before pouring
- Applied after the concrete reaches final set
Correct answer: Applied evenly to the fresh concrete surface immediately after screeding and floating
Surface retarder is applied evenly to freshly placed concrete to delay set of the surface paste, allowing it to be washed away later to expose aggregate.
Question 2: A broom finish is specified for an exterior walkway. Which broom orientation produces the most slip resistance?
- Parallel to the direction of foot traffic
- Perpendicular to the direction of foot traffic (Correct answer)
- At a 45-degree diagonal to traffic flow
- Circular broom strokes
Correct answer: Perpendicular to the direction of foot traffic
Brooming perpendicular to the direction of travel creates ridges that interrupt forward motion and provide the greatest slip resistance.
Question 3: What is the primary difference between an acid stain and a water-based concrete stain?
- Acid stains are UV-resistant; water-based stains fade quickly
- Acid stains react chemically with concrete minerals to create color; water-based stains penetrate and deposit pigment (Correct answer)
- Water-based stains require etching; acid stains do not
- Acid stains work only on new concrete; water-based stains work on old slabs
Correct answer: Acid stains react chemically with concrete minerals to create color; water-based stains penetrate and deposit pigment
Acid stains react with calcium hydroxide in the concrete to create permanent, variegated color, while water-based stains deposit pigment particles into the surface pores.
Question 4: When using a stamping tool on colored concrete, the finisher notices the pattern is becoming shallow and indistinct. What is the most likely cause?
- The concrete mix has too low a slump
- The concrete has become too stiff and the stamping window has passed (Correct answer)
- The stamps are too heavy for the pattern
- The release agent is too thick
Correct answer: The concrete has become too stiff and the stamping window has passed
If concrete stiffens beyond the optimal stamping consistency, impressions become shallow; finishers must monitor surface stiffness and work efficiently within the stamping window.
Question 5: Which sealer type provides the highest gloss and most color enhancement for decorative concrete surfaces?
- Penetrating silane/siloxane sealer
- Matte acrylic sealer
- High-solids polyurethane or epoxy sealer (Correct answer)
- Reactive lithium silicate densifier
Correct answer: High-solids polyurethane or epoxy sealer
High-solids polyurethane and epoxy sealers form a thick film that produces the highest gloss finish and significantly enhances color depth in decorative concrete.
Question 6: A concrete finisher is working on a colored slab in direct sunlight on a hot day. What special concern applies to the stamping operation?
- The pigment may bleach in UV light before stamping is complete
- The concrete will set faster, shortening the stamping window significantly (Correct answer)
- Stamps must be preheated to match surface temperature
- Heat causes color hardener to react with the base color
Correct answer: The concrete will set faster, shortening the stamping window significantly
High temperatures accelerate cement hydration, dramatically shortening the stamping window and requiring faster coordination among crew members.
Question 7: What is the correct method for neutralizing an acid stain on concrete before sealing?
- Rinse with a strong alkaline bleach solution
- Scrub with a baking soda and water solution, then rinse thoroughly with clean water (Correct answer)
- Apply a second coat of acid stain to neutralize the first
- Allow 48 hours for the acid to self-neutralize before sealing
Correct answer: Scrub with a baking soda and water solution, then rinse thoroughly with clean water
A baking soda (sodium bicarbonate) and water solution neutralizes residual acid, and thorough rinsing removes all reaction byproducts before sealer application.
ACI Color & Texture Finishing 3
When applying a surface retarder to achieve an exposed aggregate finish, how should the retarder be applied?