ACI Surface Preparation & Finishing Techniques 3

Question 1

What type of finish is achieved by dragging a stiff-bristled broom across fresh concrete?

Accepted Answer

Broom finish

Answer

A broom finish creates a textured, slip-resistant surface by dragging bristles across the concrete before it fully sets.

Question 2

An exposed aggregate finish is achieved by:

Accepted Answer

Washing away the surface mortar to reveal embedded aggregate before it fully hardens

Answer

Exposed aggregate finish involves removing surface mortar by washing or brushing while the concrete is still green, revealing the decorative coarse aggregate.

Question 3

Which chemical compound is commonly used as a surface retarder to achieve an exposed aggregate finish?

Accepted Answer

Sugar-based surface retarder

Answer

Sugar-based surface retarders are sprayed on fresh concrete to delay hardening of the top mortar layer, allowing it to be washed away to expose aggregate.

Question 4

What is the recommended technique when applying a steel trowel finish for a hard, dense surface?

Accepted Answer

Use light pressure on early passes and progressively increase pressure on later passes

Answer

Early troweling uses light pressure to smooth the surface; later passes apply increasing pressure to compact and densify the mortar layer.

Question 5

What does it mean when a finisher says the concrete has reached the 'thumbnail test' stage?

Accepted Answer

A fingernail pressed into the surface leaves only a slight indentation, indicating readiness for final finishing

Answer

The thumbnail test checks firmness — a slight indentation without sinking indicates the surface is ready for final steel troweling.

(ACI) American Concrete Institute Concrete Finisher Practice Test

(ACI) American Concrete Institute Concrete Finisher Practice Test

ACI Surface Preparation & Finishing Techniques 3