CCS Masonry & Mortar Repair Techniques 3 — Questions and Answers
Question 1: What tool is specifically designed to remove old mortar from chimney joints without damaging the brick?
- Cold chisel and hammer
- Electric angle grinder with diamond blade
- Oscillating tool with carbide grout blade (Correct answer)
- Rotary hammer drill
Correct answer: Oscillating tool with carbide grout blade
An oscillating multi-tool with a carbide grout removal blade provides controlled cutting action that removes mortar while minimizing risk to adjacent brick faces.
Question 2: Efflorescence on a chimney's brick surface is caused by:
- Bird droppings reacting with the brick surface
- Soluble salts carried to the surface by evaporating moisture (Correct answer)
- Mold and algae growth on damp masonry
- Fly ash deposits from combustion gases
Correct answer: Soluble salts carried to the surface by evaporating moisture
Efflorescence is a white crystalline deposit formed when water dissolves soluble salts within the masonry and deposits them on the surface as it evaporates.
Question 3: When using hydraulic cement to repair a chimney's water entry point, at what stage of workability should it be applied?
- As a wet, pourable slurry
- After it has fully hardened and cured
- While still plastic and pliable, just before it begins to set rapidly (Correct answer)
- Mixed very dry and pressed into place as a powder
Correct answer: While still plastic and pliable, just before it begins to set rapidly
Hydraulic cement must be shaped and pressed into place while still workable because it sets very rapidly (often in 3-5 minutes) and expands slightly as it hardens to seal the leak.
Question 4: A chimney sweep finds that the mortar between the smoke chamber corbeling is crumbling. The BEST repair approach is:
- Apply parging with a refractory or heat-resistant mortar coating (Correct answer)
- Use standard Type S mortar to repoint each individual joint
- Apply a layer of silicone caulk to seal the gaps
- Leave it alone if the chimney is still drawing properly
Correct answer: Apply parging with a refractory or heat-resistant mortar coating
Parging the smoke chamber with a refractory mortar provides a smooth, heat-resistant coating that seals the corbeled joints and improves draft efficiency.
Question 5: What is the primary function of lime in mortar mixes used for chimney repointing?
- It increases the compressive strength of the mortar
- It provides plasticity, water retention, and allows slight flex to accommodate movement (Correct answer)
- It accelerates the curing time of portland cement
- It acts as a waterproofing agent for the joint
Correct answer: It provides plasticity, water retention, and allows slight flex to accommodate movement
Lime adds workability and plasticity to mortar while allowing minor movement without cracking, which is critical for chimneys subject to thermal cycling.
Question 6: When repairing a cracked chimney crown, which material is most appropriate for sealing hairline cracks before applying a crown coat?
- Portland cement slurry
- Flexible elastomeric crown sealant (Correct answer)
- Hydraulic cement
- Epoxy resin filler
Correct answer: Flexible elastomeric crown sealant
Flexible elastomeric sealants are designed to bridge hairline cracks and remain flexible through freeze-thaw cycles, preventing future water infiltration.
Question 7: At what minimum ambient temperature should masonry repointing work be performed to ensure proper mortar curing?
- Above 20°F (-7°C)
- Above 40°F (4°C) (Correct answer)
- Above 50°F (10°C)
- Above 60°F (15°C)
Correct answer: Above 40°F (4°C)
ASTM C270 and masonry guidelines require ambient temperatures above 40°F (4°C) and rising during mortar application to prevent freezing before adequate strength develops.
CCS Masonry & Mortar Repair Techniques 3
What tool is specifically designed to remove old mortar from chimney joints without damaging the brick?