CTI Surface Preparation & Adhesives 3 — Questions and Answers
Question 1: When preparing a wood subfloor for tile installation, what is the maximum allowable deflection under live load according to TCNA?
- L/120
- L/240
- L/360 (Correct answer)
- L/480
Correct answer: L/360
TCNA requires a subfloor deflection of no more than L/360 of the span under live load to prevent tile and grout cracking.
Question 2: What is a primary advantage of using a medium-bed mortar over standard thin-set?
- Faster cure time
- Ability to fill voids up to 3/4 inch without slumping (Correct answer)
- Lower cost per square foot
- Greater flexibility when cured
Correct answer: Ability to fill voids up to 3/4 inch without slumping
Medium-bed mortars are formulated to support large/heavy tiles at greater mortar depths (up to 3/4 inch) without slumping.
Question 3: An epoxy adhesive is specified for a commercial kitchen floor. What is a critical characteristic of mixing and using epoxy mortar?
- It must be mixed with water at a 1:3 ratio
- It has a limited pot life and must be used within the working time (Correct answer)
- It requires a 72-hour cure before grouting
- It cannot be used with porcelain tile
Correct answer: It has a limited pot life and must be used within the working time
Epoxy mortars have a finite pot life once mixed; unused material hardens and must be discarded, making working time critical.
Question 4: How should existing ceramic tile be prepared before applying a new tile installation over it?
- Grind all grout joints flush with the tile surface
- Clean, ensure bond, fill cracks, and scarify glossy surfaces (Correct answer)
- Apply a skim coat of gypsum plaster
- Remove all existing tile before proceeding
Correct answer: Clean, ensure bond, fill cracks, and scarify glossy surfaces
Existing tile must be cleaned, tested for bond, have cracks repaired, and glossy surfaces scarified or primed to ensure adhesion.
Question 5: What does the ANSI A118.11 standard specify?
- Standard specifications for organic adhesives
- Standard specifications for EGP (Exterior Glue Plywood) latex portland cement mortars (Correct answer)
- Standard specifications for crack isolation membranes
- Standard specifications for grout
Correct answer: Standard specifications for EGP (Exterior Glue Plywood) latex portland cement mortars
ANSI A118.11 covers EGP (Exterior Glue Plywood) latex portland cement mortars used for bonding tile to plywood.
Question 6: A tile installer is working on a slab with a pH reading of 10. What action should be taken?
- Proceed normally; pH 10 is acceptable
- Apply a neutralizing primer before installation (Correct answer)
- Install immediately with epoxy mortar only
- Wait 90 days before installing
Correct answer: Apply a neutralizing primer before installation
A pH above 9 indicates high alkalinity; a neutralizing primer or treatment should be applied before adhesive installation.
Question 7: What is the function of a non-sag or non-slump mortar additive?
- To increase the open time of the mortar
- To prevent tile from sliding on vertical surfaces during installation (Correct answer)
- To add color to the mortar
- To reduce the water-to-cement ratio
Correct answer: To prevent tile from sliding on vertical surfaces during installation
Non-sag mortars contain additives that provide thixotropic properties, preventing tiles from sliding down vertical surfaces before they set.
CTI Surface Preparation & Adhesives 3
When preparing a wood subfloor for tile installation, what is the maximum allowable deflection under live load according to TCNA?