MHIC Construction Methods and Materials 6 — Questions and Answers
Question 1: During a bathroom renovation, a homeowner wants to tile directly over an existing drywall surface in a wet zone (shower walls). What should the contractor do?
- Apply a waterproofing membrane over the drywall and then tile
- Remove the drywall and install cement board or a tile backer designed for wet areas (Correct answer)
- Install the tile directly using a high-quality mastic adhesive, which provides sufficient moisture resistance
- Apply two coats of primer to the drywall before tiling
Correct answer: Remove the drywall and install cement board or a tile backer designed for wet areas
Standard drywall (gypsum board) deteriorates when exposed to repeated moisture even with a waterproofing membrane on top. The correct approach is to remove it and install a proper tile backer such as cement board, fiber-cement board, or an equivalent wet-area substrate. These materials are dimensionally stable and will not degrade behind tile in shower applications.
Question 2: A contractor is installing a load-bearing wall using light-gauge steel framing in a residential project. What is the minimum yield strength typically required for structural steel framing members used in load-bearing applications?
- 25 ksi (kilopounds per square inch)
- 33 ksi (kilopounds per square inch) (Correct answer)
- 50 ksi (kilopounds per square inch)
- 65 ksi (kilopounds per square inch)
Correct answer: 33 ksi (kilopounds per square inch)
Steel framing members used in load-bearing applications typically require a minimum yield strength of 33 ksi (33,000 psi), as specified by AISI standards. This grade (commonly ASTM A653 Grade 33) provides the structural integrity needed for load-bearing walls while remaining workable for field fabrication.
Question 3: A contractor is pouring a concrete slab on grade in cold weather (ambient temperature 35°F). Which of the following practices is MOST important to prevent freeze damage to the fresh concrete?
- Add extra water to the mix to keep the concrete workable longer
- Use accelerating admixtures and maintain the concrete temperature above 50°F during curing (Correct answer)
- Pour the slab at night to take advantage of cooler, more stable temperatures
- Increase the water-to-cement ratio to generate more heat of hydration
Correct answer: Use accelerating admixtures and maintain the concrete temperature above 50°F during curing
In cold weather concreting, accelerating admixtures (such as calcium chloride in non-reinforced slabs) help speed up strength gain, and maintaining concrete temperature above 50°F (per ACI 306) ensures proper hydration and prevents freezing before the concrete achieves adequate strength. Adding water or increasing the water-to-cement ratio actually weakens the mix and should never be done.
Question 4: When framing a door rough opening in a wood-framed exterior wall, what is the purpose of the jack stud (also called a trimmer stud)?
- To transfer roof loads around the opening down to the foundation
- To provide a nailing surface for interior door casing trim only
- To bear the load of the header and transfer it to the bottom plate (Correct answer)
- To act as a fire block within the wall cavity
Correct answer: To bear the load of the header and transfer it to the bottom plate
The jack stud (trimmer stud) runs vertically alongside the king stud and supports the ends of the header directly. It bears the header's load — which includes any loads transferred from above — and transfers that load down through the bottom plate to the foundation. The king stud provides lateral stability, but the jack stud is the direct vertical support for the header.
Question 5: A contractor installs a new asphalt shingle roof and notices the existing roof deck has areas of oriented strand board (OSB) with surface delamination and soft spots. What is the correct corrective action before shingling?
- Apply roofing cement over the delaminated areas to re-bond the surface veneers
- Sister new OSB panels alongside the damaged sections to add stiffness
- Cut out and replace all deteriorated or structurally compromised OSB panels (Correct answer)
- Cover the damaged OSB with a layer of 15-lb felt paper as a moisture barrier before shingling
Correct answer: Cut out and replace all deteriorated or structurally compromised OSB panels
Delamination and soft spots in OSB indicate moisture damage and structural degradation. Applying roofing cement or felt paper over compromised decking does not restore structural integrity and can trap moisture, worsening the problem. The correct action is to cut out and replace all damaged sections with new sheathing to provide a solid, uniform nailing surface and proper load distribution for the shingles.
Question 6: Which type of foundation is most appropriate when building on expansive clay soils that shrink and swell significantly with moisture changes?
- Shallow spread footings sized for the soil's bearing capacity
- A post-and-beam foundation with isolated piers
- A drilled pier (caisson) foundation extending below the active zone of soil movement (Correct answer)
- A rubble trench foundation with free-draining gravel
Correct answer: A drilled pier (caisson) foundation extending below the active zone of soil movement
Expansive clays cause significant heave and settlement in the 'active zone' — the depth where moisture changes occur seasonally. Drilled piers (caissons) extend through this active zone into stable soil or bedrock below, anchoring the structure against the vertical movement. Shallow spread footings and isolated piers would be subject to the same expansive forces and are not suitable without special engineering measures.
MHIC Construction Methods and Materials 6
During a bathroom renovation, a homeowner wants to tile directly over an existing drywall surface in a wet zone (shower walls).
What should the contractor do?