Exploring the Construction Quality Control of the Combination System of Sloping Roof Cement Tiles and Finished Eaves and Gullies

2026-03-18 16:31:20

Construction Quality Control of Sloped Roof System & Prefabricated Gutter

Project: Qingdao Workers’ Hot Spring Sanatorium

1、Project Overview

• Above-ground area: approx. 18,352.00 m²

• Underground area: 16,220.41 m²

• The 1st and 2nd basement floors: parking garage, equipment rooms, civil air defense area, etc.

• The 1st and 2nd basement floors at the main building: equipment rooms, functional rooms, offices, etc.

• Building 10#, 1st floor: outdoor hot spring pools, changing rooms, toilets, power distribution area, etc.

• Building 10#, 2nd and 3rd floors: guest rooms.

• Building 4#: all guest rooms.

• North of Building 10: RV area with 46 fixed RVs.

Construction Details of the Sloped Roof

1. Finished block tiles (Cement Tiles)

2. Tile battens: 30×30 mm, spacing according to tile specifications

3. Counter battens: 40×20 mm, spacing 500 mm

4. 35‑mm‑thick C20 fine aggregate concrete leveling layer,

   equipped with welded wire mesh Φ4 @ 100×100 mm, tied with Φ10 rebar

5. Extruded polystyrene (XPS) insulation layer

6. One layer of 4‑mm‑thick polymer‑modified asphalt SBS waterproof membrane

7. 20‑mm‑thick 1:2.5 cement mortar leveling layer

8. Cast‑in‑place reinforced concrete roof slab.

   Embedded anchor bolts Φ10 @ 900×900 mm, extending 25 mm into the batten layer.

   
   

2. Quality Control of Sloped Roof Structural Slab Construction

Formwork and Support System

• Bottom formwork: 12‑mm‑thick high‑strength bamboo plywood, smooth surface, free of warping, cracking or delamination.

• Supports: 80×50 mm wood joists (no serious decay, cracking or warping);

  Φ48×3.5 mm standard steel pipes and couplers (no serious rust, bending or cracks).

• Vertical poles: 900×900 mm spacing

• Horizontal ledgers: 1.5 m spacing

• A bottom ledger at 150 mm above ground

• An additional ledger along the roof slope directly below the slab to form a grid structure.

  A 50×200 mm continuous bearing pad is set under each pole.

2. Reinforcement Works

• Concrete cover thickness

• Effective height of slab reinforcement

• Overall stability and anti‑stepping performance of the mesh

3. Concrete Works

• 10–20 mm crushed stone is used for better compaction.

• Medium-coarse sand with fineness modulus M = 2.8 reduces water consumption by 20–25 kg/m³ compared with M = 2.3, avoiding a high water‑cement ratio.

• Fly‑ash blended cement is used to reduce cement content, improve workability, lower hydration heat, and produce denser, stronger and more durable concrete.

• The top form is partially closed, width approx. 1000 mm

• A 600‑mm pouring slot is reserved for placing and vibrating

• A movable baffle prevents aggregate sliding

• The shrinkage rate before hardening is 10–30 times higher than after hardening.

3. Quality Control of Sloped Roof Waterproofing

1. Primer application

   Cold primer is applied with a long‑handle brush to a clean, dry base;

   detail areas are touched up with a paintbrush.

   No blank areas, uniform coating.

   Allow to dry for ≥ 4 hours until non‑sticky before proceeding.
2. Additional waterproof layers

   All internal/external corners, wall‑to‑roof joints, equipment base transitions are reinforced.

   Each side of the additional layer ≥ 250 mm wide.
3. Membrane layout and alignment

   Reference lines are snapped on the base.

   Membranes are laid lengthwise, perpendicular to the drainage direction.

   Laps follow the downhill flow, not reverse.

   Start from concentrated drainage areas (e.g., gutters), from low to high elevation.
4. Membrane placement

   A high‑pressure blowtorch heats the junction of membrane and base evenly.

   Once the surface melts, the roll is rolled forward and bonded.

   For plane‑to‑vertical transitions:

• Lay the horizontal part first, then upwards along the vertical

• Fully adhere to internal corners, no voids

• Vertical walls fully bonded

• Joints rolled compact and firmly bonded

5. Internal and external corners

   After base treatment, an additional layer is applied, cut to shape and fully bonded.

4. Quality Control of Cement Tile Installation

1. Tile Layout and Line Setting

1. Vertical direction

   Based on main tile dimensions and a minimum 50‑mm lap, the effective coverage length is determined.

   Tiles are laid from bottom to top perpendicular to the eave, upper tiles overlapping lower ones.

   Tiles can be cut at the ridge.
2. Horizontal direction

• Typical roof: lay main tiles first, then right‑side tiles to maintain a regular edge.

• Regular polygonal roof: layout from the center to both sides, cut at the ridge.

3. Main tiles

   Generally laid in an “S”‑shape pattern, with joints at the highest point of the tile rib.

   Tight, small‑gap S‑joints resist crosswind and minimize rain penetration.

2. Fixing of Battens via Rebar Tying

1. Horizontal tying: spaced by one main tile, staggered at laps.

2. Vertical spacing: 1 m.

3. Rebar at the ridge must be firmly tied (hook‑bent connection).

3. Copper Wire Tying and Mortar Bedding

1. Each tile secured with 18# double‑strand copper wire.

2. Copper wire is passed through tile holes; tiles are bedded in 1:3 cement mortar on the protective layer.

   Ridge tiles use bonding mortar for extra strength.

3. During installation, copper wire is temporarily folded upward;

   after the tile is firmly bedded, the wire is tied to the batten.

4. A horizontal line is stretched to ensure alignment.

5. Tile surfaces are kept clean; mortar and debris are removed immediately.

4. Detail Treatment

1. Ridges, eaves, peaks

   Tile joints are filled and troweled with hemp fiber mortar to prevent water penetration and crosswind intrusion.
2. Internal corners without gutter tiles

   A cement mortar drainage trough is formed.

   After tiles are laid and joints sealed:

• Apply a leveling layer

• Add an extra waterproof layer

• Apply and trowel a protective layer

3. Finished slope roof

   After all tiles are installed and joints sealed,

   exterior paint matching the mortar color is applied.
   
   

5. Quality Control of Prefabricated Gutter Installation

1. Prefabricated gutters are factory‑prefabricated based on detailed shop drawings approved and signed by the design institute.

2. Main steel keel: control elevation, embedded parts and welding quality.

3. After keel installation, aluminum panels are fixed with Steel nails to avoid warping and provide a smooth surface for membrane lapping.

4. Sealant between aluminum panels is critical to prevent future leakage.

   Protection during construction is required to avoid sealant cracking from stepping.

5. Care is taken during waterproof membrane installation to avoid damaging panel joints.

   
   

6. Quality Control of Waterproofing at Gutter‑to‑Sloped Roof Joints

1. After roof waterproofing is completed, extend the membrane 200 mm beyond the eave for later lapping.

2. During gutter installation, secure aluminum laps and wall‑connected panels to prevent warping; apply sealant evenly.

3. After keel and aluminum works are finished,

   bond the reserved waterproof membrane to the gutter aluminum surface.

   This ensures rainwater and seepage under tiles drain into the gutter,

   preventing water penetration below the waterproof layer or into insulated walls.

   
   

7. Conclusion