Surface Preparation & Finishing Techniques Flashcards

What is the primary purpose of screeding concrete after placement?

Answer: To strike off excess concrete and establish grade

Screeding strikes off excess concrete and brings the surface to the desired grade or elevation.

Which finishing tool is used immediately after screeding to embed aggregate and bring mortar to the surface?

Answer: Bull float

A bull float is used right after screeding to embed coarse aggregate and bring cement paste to the surface.

When should a finisher begin hand floating operations?

Answer: When the bleed water sheen has disappeared and the surface can support a finisher's weight

Hand floating begins when surface bleed water has evaporated and the concrete is firm enough to support a finisher without excessive indentation.

What defect results from troweling concrete before bleed water has evaporated?

Answer: Delamination

Troweling too early traps bleed water under the surface, causing delamination where the top layer separates from the base.

In which direction should a darby or bull float be pushed across fresh concrete?

Answer: In overlapping arcs, keeping the leading edge slightly raised

Darbies and bull floats are worked in overlapping passes with the leading edge slightly raised to avoid digging into the surface.

What is the purpose of edging concrete flatwork?

Answer: To create a rounded, durable edge that resists chipping

Edging rounds and densifies the slab perimeter to produce a smooth, chip-resistant edge.

What spacing is typically recommended for hand-jointing (grooving) a 4-inch thick concrete slab to control cracking?

Answer: 10 times the slab thickness in inches (approximately)

Control joints are typically spaced at intervals of 24–36 times the slab thickness, or roughly 8–12 feet for a 4-inch slab.