CTI CTI Substrate Preparation & Assessment 2 — Questions and Answers
Question 1: Which ASTM standard governs the in-situ relative humidity testing of concrete slabs using embedded probes?
- ASTM F1869
- ASTM F2170 (Correct answer)
- ASTM E1745
- ASTM C627
Correct answer: ASTM F2170
ASTM F2170 covers the standard test method for determining relative humidity in concrete floor slabs using in-situ probes.
Question 2: A CTI inspector is evaluating an existing terrazzo floor as a substrate for new tile. What is the primary concern?
- Terrazzo is too soft to support tile weight
- Terrazzo surfaces are often too smooth for mortar bond without surface preparation (Correct answer)
- Terrazzo expands too much thermally
- Terrazzo must be removed and cannot serve as a substrate
Correct answer: Terrazzo surfaces are often too smooth for mortar bond without surface preparation
Existing terrazzo is typically dense and smooth, requiring mechanical scarification or shot-blasting to create a bondable surface profile before tile installation.
Question 3: What does the term 'flatness' refer to when assessing a substrate for tile installation?
- The slope or pitch of the surface for drainage
- The absence of high and low spots over a defined measurement length (Correct answer)
- The structural rigidity of the substrate
- The absence of cracks in the substrate
Correct answer: The absence of high and low spots over a defined measurement length
Flatness refers to the planarity of a surface — ANSI A108.02 requires floors to be flat within 1/8 inch in 10 feet and 1/16 inch in 2 feet.
Question 4: When inspecting a radiant heat slab, what additional substrate consideration is critical before tile installation?
- The slab must be at least 6 inches thick
- The radiant system must be cycled (run then cool) before tiling to release residual moisture (Correct answer)
- Radiant slabs require a membrane before tiling
- Tile cannot be installed over radiant heat systems
Correct answer: The radiant system must be cycled (run then cool) before tiling to release residual moisture
Radiant heat slabs should be operational prior to tile installation to drive out residual moisture and allow the slab to stabilize before moisture testing.
Question 5: What is the required compressive strength of a concrete substrate before tile can be installed per ANSI A108 standards?
- 1,500 psi minimum
- 2,500 psi minimum (Correct answer)
- 3,500 psi minimum
- 5,000 psi minimum
Correct answer: 2,500 psi minimum
ANSI A108 requires a minimum concrete compressive strength of 2,500 psi for tile substrates to ensure adequate structural integrity.
Question 6: A CTI inspector finds that a plywood subfloor panel is delaminating. What is the proper recommendation?
- Apply a penetrating primer and proceed with installation
- Fill delaminated areas with patching compound
- Replace the delaminated panels before any tile installation (Correct answer)
- Install a layer of cement board over the delaminated area
Correct answer: Replace the delaminated panels before any tile installation
Delaminated plywood panels have lost structural integrity and must be replaced entirely before tile installation, as patching will not restore adequate bond or stiffness.
CTI CTI Substrate Preparation & Assessment 2
Which ASTM standard governs the in-situ relative humidity testing of concrete slabs using embedded probes?