Chapter 28 Quiz: Drywall, Plaster, and Interior Walls

Multiple Choice

1. You are tiling a shower surround and need to select the correct substrate. Which material is the appropriate choice?

a) Standard 1/2-inch drywall b) Green board (moisture-resistant drywall) c) Cement board (Hardiebacker, Durock) d) 5/8-inch Type X fire-rated drywall

2. You are hanging a drywall screw and the clutch on your screw gun sets it too deep, breaking through the paper facing. The correct response is:

a) Drive the screw a little deeper so the head is well below the surface b) Fill the torn paper with joint compound — it will hold fine c) Drive the screw in further 2 inches away and leave the broken one in place d) Remove the screw, fill the hole, and drive a new screw 2 inches away from the failed location

3. The standard three-coat drywall finishing process in order is:

a) Fill coat, tape coat, finish coat b) Tape coat (bed), fill coat, finish coat c) Primer coat, tape coat, finish coat d) Fill coat, skim coat, tape coat

4. The "California patch" technique for medium-sized drywall holes is best described as:

a) Using a self-adhesive mesh patch with setting-type compound b) Cutting a patch piece with paper wings that embed directly in joint compound, requiring no backing hardware c) Screwing backing boards behind the hole and fastening a new drywall piece to them d) Using hydraulic cement to fill the hole in layers

5. A homeowner with plaster walls presses their palm against a section of the ceiling and feels slight movement, and tapping produces a hollow sound. This indicates:

a) The ceiling is properly installed and the hollow sound is normal for plaster b) The plaster has lost its mechanical keys and has delaminated from the lath c) There is a void in the gypsum core from the original installation d) The horse hair in the plaster has deteriorated, requiring full removal

6. What is the primary mechanism by which resilient channels improve soundproofing performance?

a) They add significant mass to the wall assembly b) They absorb sound within the wall cavity using their metal geometry c) They physically decouple the drywall face from the stud framing, interrupting vibration transmission d) They create air gaps that reflect sound waves back toward the noise source

7. Adding acoustic foam tiles to a shared wall between two apartments will:

a) Reduce sound transmission by approximately 10 STC points b) Reduce room echo and reverberation but have essentially no effect on sound transmission between rooms c) Improve performance primarily for low-frequency bass sounds d) Perform as well as a resilient channel installation at one-quarter the cost

8. Fresh drywall must be primed before painting primarily because:

a) Paint does not bond to gypsum without a chemical primer layer b) The paper facing and joint compound have different porosity that causes uneven paint absorption and seam shadowing c) Paint color changes chemically when applied to unpainted gypsum d) Code requires primer on all new construction surfaces

9. Which paint sheen is most appropriate for a kitchen or bathroom wall where cleaning and moisture resistance are priorities?

a) Flat/matte b) Eggshell c) Semi-gloss d) Any sheen with premium-grade paint works equally well in wet areas

10. The Level 5 drywall finish (skim coat over entire surface) is specifically required for:

a) Any painted surface in a residential home b) Surfaces that will receive flat paint in low-traffic areas c) Surfaces that will receive gloss or semi-gloss paint or are subject to raking light from large windows d) Surfaces in kitchens and bathrooms regardless of paint sheen

Short Answer

11. Explain what drywall "shadowing" or "picture framing" is, what causes it, and how it is prevented.

12. What is the difference between using paintable latex caulk versus joint compound for repairing a hairline crack in a plaster wall? When is each more appropriate?

13. A homeowner wants to reduce sound transmission through a wall between their home office and the living room. They're considering: (A) adding a second layer of drywall directly over the existing, or (B) removing the existing drywall, installing resilient channels, adding acoustic insulation in the cavity, and rehanging drywall. Describe the expected performance difference and cost difference between the two approaches.

14. What does a "short-circuited" resilient channel mean, and why does it matter?

15. Describe two visual or tactile signs that a plaster wall may have failing keys, and explain what a plaster washer does to address this problem.

Answer Key

Multiple Choice: 1-c, 2-d, 3-b, 4-b, 5-b, 6-c, 7-b, 8-b, 9-c, 10-c

Short Answer Guidance:

11. Shadowing (or picture framing) is the appearance of drywall seams and patches visible through the painted finish as slight variations in sheen or texture. It is caused by differential porosity: bare drywall paper absorbs paint differently than joint compound, and unprimed surfaces allow these differences to show through. It is prevented by applying a full coat of PVA drywall primer before any topcoat, equalizing the surface porosity so paint dries uniformly.

12. Latex caulk is flexible and remains so after curing, making it superior for cracks that will see ongoing minor movement — common in plaster at structural locations like beam lines and corners. It does not shrink. Joint compound or patching plaster is appropriate for stable cracks in the field of the wall where no movement is occurring; it creates a harder surface that accepts paint and texture more similarly to the surrounding plaster. Using rigid compound on a moving crack will result in the crack reopening through the repair.

13. Adding a second layer of drywall directly (Option A) increases mass slightly, improving STC by approximately 3–5 points. This may be perceptible but is generally not transformative — the room still transmits conversation at reduced volume. Cost: $800–$2,000 including materials and labor for an average room. Resilient channel installation (Option B) adds the critical decoupling element in addition to mass, improving STC by 10–15 points over the existing baseline — a meaningful, perceptible difference (near-inaudible conversation to full inaudibility). Cost: $2,500–$5,000 for an average room. Option B costs roughly twice as much but delivers three to four times the acoustic improvement.

14. A short-circuited resilient channel is one where a drywall screw has accidentally been driven through the channel and into the stud framing behind it, creating a rigid mechanical connection between the drywall face and the framing — exactly what the channel system is designed to prevent. A single short-circuit in a wall effectively eliminates most of the channel system's decoupling benefit, because vibration now has a direct path from framing to drywall face. The term "short-circuit" is analogous to electrical usage — a direct, unintended path that bypasses the intended resistance.

15. Two signs of failing keys: (1) Hollow sound when tapping — solid, well-keyed plaster produces a flat thud; delaminated plaster sounds hollow and resonant; (2) Slight movement when pressing firmly with the palm — intact plaster is essentially immovable; delaminated plaster may flex slightly or produce a crackling/crunching sound. A plaster washer is a large-diameter flat metal washer with a screw hole in the center. Driving a drywall screw through the washer and into the lath or framing behind the plaster draws the plaster back against the lath mechanically, re-establishing a firm attachment despite the failed keys. The washer distributes the clamping force over a larger area, preventing the screw from pulling through the brittle plaster.