CTI Grouting & Finishing Techniques 2 — Questions and Answers
Question 1: When grouting a floor with large-format tiles (24"x24" or larger), which grout joint width is typically the minimum recommended to allow for lippage tolerance?
- 1/16 inch
- 1/8 inch (Correct answer)
- 3/16 inch
- 1/4 inch
Correct answer: 1/8 inch
Large-format tiles generally require a minimum 1/8-inch grout joint to accommodate slight warpage and lippage inherent in manufacturing.
Question 2: What is the primary purpose of back-buttering tile edges before grouting a stone installation?
- To improve grout adhesion to the tile face
- To prevent grout from bonding to the tile surface
- This is not a recommended practice
- To fill voids left by the notched trowel (Correct answer)
Correct answer: To fill voids left by the notched trowel
Back-buttering tile edges before grouting fills voids beneath tile edges that notched trowel ridges may not have fully covered.
Question 3: Efflorescence appearing on a grouted tile surface is caused by:
- Excess pigment migrating to the surface
- Soluble salts carried to the surface by water migration (Correct answer)
- Improper mixing of the grout powder
- UV degradation of polymer additives
Correct answer: Soluble salts carried to the surface by water migration
Efflorescence is a white crystalline deposit formed when water carries soluble salts through the grout and they crystallize on the surface as water evaporates.
Question 4: Which tool is best suited for packing grout into joints on a mosaic tile installation with small joints?
- A margin trowel
- A hard rubber float (Correct answer)
- A sponge float
- A notched trowel
Correct answer: A hard rubber float
A hard rubber float provides the firmness needed to force grout deeply into the small joints of mosaic installations without tearing the mesh backing.
Question 5: After grouting, you notice grout haze has dried on a polished marble surface. What should you use to remove it?
- A green scrub pad with water
- A manufacturer-approved grout haze remover safe for natural stone (Correct answer)
- Muriatic acid solution diluted 10:1
- A steam cleaner
Correct answer: A manufacturer-approved grout haze remover safe for natural stone
Only a stone-safe, non-acidic grout haze remover should be used on polished marble, as acids and abrasive pads will permanently damage the finish.
Question 6: What does the ANSI A108.10 standard specifically address regarding grout?
- Installation of ceramic tile with latex-portland cement mortar
- Installation of grout in tile work (Correct answer)
- Specifications for epoxy adhesive mortar systems
- Requirements for waterproofing membranes under tile
Correct answer: Installation of grout in tile work
ANSI A108.10 covers installation of grout in tile work, providing the industry standard specifications for grouting procedures.
Question 7: When installing glass tile, which grout characteristic is most critical to prevent telegraphing through the tile face?
- High compressive strength
- White or matching color with no aggregate larger than joint width (Correct answer)
- Rapid-setting properties
- High resistance to chemical cleaners
Correct answer: White or matching color with no aggregate larger than joint width
Glass tile is translucent, so grout color must match or complement the tile and aggregate particle size must not exceed joint width to prevent visible texture behind the glass.
CTI Grouting & Finishing Techniques 2
When grouting a floor with large-format tiles (24"x24" or larger), which grout joint width is typically the minimum recommended to allow for lippage tolerance?