CTI Substrate Preparation & Waterproofing Flashcards

Before installing tile over a new concrete slab, a CTI inspector should confirm the slab has cured for a minimum of how many days?

Answer: 28 days

Concrete requires a minimum 28-day cure to achieve design strength and reduce moisture levels that could cause bond failure.

Which condition describes uneven moisture absorption across a substrate surface that can cause inconsistent mortar bond strength?

Answer: Differential suction

Differential suction occurs when areas of the substrate absorb mortar water at different rates, leading to variable bond strength.

A CTI inspector finds white powdery deposits on a tile surface. This efflorescence most likely indicates:

Answer: Water migrating through the assembly and depositing soluble salts on the surface

Efflorescence is caused by water carrying soluble salts through the tile assembly; the salts are left behind as white deposits when the water evaporates.

Why does a wood-framed floor system typically require a cleavage membrane before a mortar bed tile installation?

Answer: Wood expands and contracts with moisture changes, requiring isolation from the mortar bed

Wood substrates are subject to moisture-induced movement, so a cleavage membrane isolates the mortar bed and prevents wood movement from cracking the tile.

What is the minimum required overlap for sheet waterproofing membrane seams in a wet-area tile installation?

Answer: 2 inches

Sheet membrane seams must overlap at least 2 inches and be fully bonded to create a continuous, leak-free waterproofing layer.

In a steam shower installation, the waterproofing membrane must cover:

Answer: The entire ceiling in addition to all walls and the floor

Steam showers require full waterproofing of all surfaces including the ceiling because steam condenses everywhere and can cause widespread water damage.