CFI Tile & Stone Installation 3 — Questions and Answers
Question 1: Which type of mortar is specifically designed for use with glass tile installations?
- Gray sanded mortar
- White non-sanded polymer-modified mortar (Correct answer)
- Rapid-setting floor mortar
- Epoxy mortar
Correct answer: White non-sanded polymer-modified mortar
White non-sanded polymer-modified mortar prevents color show-through and provides the flexibility needed for glass tiles.
Question 2: What should an installer do when encountering a crack in a concrete substrate before installing tile?
- Fill the crack with thinset and tile immediately
- Apply a crack isolation membrane over the crack (Correct answer)
- Grind the crack smooth and proceed
- Install backerboard directly over the crack
Correct answer: Apply a crack isolation membrane over the crack
A crack isolation membrane prevents existing cracks from reflecting through the tile assembly.
Question 3: When setting a 12-inch tile, what size V-notch trowel is typically specified to achieve proper mortar ridge collapse and coverage?
- 1/8" x 1/8" x 1/8"
- 3/16" x 5/32" x 5/32"
- 1/4" x 3/8" x 1/4" (Correct answer)
- 1/2" x 1/2" x 1/2"
Correct answer: 1/4" x 3/8" x 1/4"
A 1/4" x 3/8" x 1/4" V-notch trowel provides sufficient mortar volume for 12-inch tiles to achieve full contact when collapsed.
Question 4: What is the correct sequence of steps when installing a mortar bed (mud bed) for tile?
- Wet mix, pack, screed, tile immediately
- Apply cleavage membrane, pack mortar, screed to grade, allow to cure, then tile (Correct answer)
- Screed first, then pack mortar on top
- Apply mortar dry, mist with water, then screed
Correct answer: Apply cleavage membrane, pack mortar, screed to grade, allow to cure, then tile
The proper sequence is membrane, pack, screed, then allow the bed to cure before tiling to prevent settlement.
Question 5: When installing natural stone tile on a floor, why is a penetrating sealer applied before grouting?
- To increase stone hardness
- To prevent grout from staining the stone surface (Correct answer)
- To improve mortar bond to the stone
- To fill micro-cracks in the stone
Correct answer: To prevent grout from staining the stone surface
Penetrating sealers protect porous stone from grout staining during the grouting process.
Question 6: What type of grout is most appropriate for joints less than 1/8 inch wide?
- Sanded grout
- Unsanded (non-sanded) grout (Correct answer)
- Epoxy grout with fine aggregate
- Portland cement mortar
Correct answer: Unsanded (non-sanded) grout
Unsanded grout is formulated for narrow joints under 1/8 inch; sand particles in sanded grout are too large for these joints.
Question 7: On a wood-framed floor, what is the recommended total thickness for a mortar bed installation to provide adequate stiffness for tile?
- 1/2 inch minimum
- 3/4 inch minimum
- 1-1/4 inches minimum (Correct answer)
- 2 inches minimum
Correct answer: 1-1/4 inches minimum
TCNA guidelines recommend a minimum 1-1/4 inch mortar bed thickness over wood framing to reduce deflection risk.
CFI Tile & Stone Installation 3
Which type of mortar is specifically designed for use with glass tile installations?