CTI CTI Substrate Preparation & Waterproofing 2

Question 1

What is the minimum thickness of a Portland cement mortar bed for a floor tile installation per TCNA standards?

Accepted Answer

3/4 inch

Answer

TCNA specifies a minimum mortar bed thickness of 3/4 inch for floor installations to provide adequate structural support.

Question 2

Which ASTM standard governs the in-situ relative humidity probe test for concrete slab moisture?

Accepted Answer

ASTM F2170

Answer

ASTM F2170 covers the in-situ relative humidity probe test, where probes are inserted into drilled holes in the slab.

Question 3

How should a CTI inspector recommend correcting a substrate with excessive high spots and low spots before tiling?

Accepted Answer

Grind high spots and fill low spots with patching compound

Answer

Both high spots must be ground down and low spots filled to achieve a flat substrate meeting the required tolerance.

Question 4

What is the maximum substrate flatness tolerance for large-format tiles with any side 15 inches or longer?

Accepted Answer

1/8 inch in 10 feet

Answer

TCNA recommends no more than 1/8 inch variation in 10 feet for large-format tiles to prevent visible lippage.

Question 5

What material is typically used to bond a secondary waterproofing membrane to a substrate around shower niches and corners?

Accepted Answer

Thinset mortar per the membrane manufacturer's specifications

Answer

The membrane manufacturer specifies the bonding material — typically unmodified or modified thinset — to ensure compatibility and maintain warranty coverage.

CTI - Certified Tile Inspector Practice Test

CTI - Certified Tile Inspector Practice Test

CTI CTI Substrate Preparation & Waterproofing 2