Masonry Case Study: Fast, Compliant Blockwork Delivery on a High-Rise Core

Project at a glance Scope: Supply & install concrete masonry blockwork (hollow and solid), stiffener columns, lintels, control joints, and fire-stopping interfaces within a tower project core. Context: Live multi-trade environment (MEP, plaster, ceilings) with stringent QA/QC and ITP hold-points. Targets: Dimensional accuracy, crack control, compliant reinforcement, and fire/deflection details coordinated to shop drawings. (This case study is based on our internal method statement and marked-up shop details used on a comparable tower package.)

The challenge

Core blockwork had to be executed without disrupting MEP and finishing trades, while meeting tight tolerances and service penetrations. We also needed to control cracking on tall wall panels, maintain fire integrity at slabs/ceilings, and achieve clean alignment across long wall runs with multiple openings—all under active inspections and material compliance controls. 

Our approach

1) Pre-start controls & set-out

• Toolbox talks, PPE, edge protection, lighting & welfare were verified and logged.
• Survey set-out completed against approved shop drawings; IR/PCP inspections raised 24 h prior to first course.
• Materials on pallets, moisture limits checked; random compressive strength sampling planned by QCE. 

2) Materials & mix design

• Blocks: Approved units (nominal tolerances checked).
• Mortar (examples):
  • Type S (load-bearing): 1 part Portland cement : 0.5 hydrated lime : 4 parts sand.
  • Type N (general): 1 : 1 : 5–6 (cement : lime : sand).
• Water: Potable, chloride/sulphate limits to BS. 

3) Reinforced masonry strategy

• Stiffener columns at ~6 m centres using 4T12 vertical bars + T6 stirrups @200 mm; columns dowelled to slabs.
• Vertical wall reinforcement: typical T16 bars @1200 mm c/c;
• Horizontal control: galvanised steel mesh every two courses;
• Grouting: C24/30 concrete grout with 10 mm max aggregate into hollows, bond beams, and around bars/lintels.
• Openings/lintels: Concrete lintels reinforced to tabulated spans; sides of openings vertically reinforced and grouted.

4) Movement, deflection & fire details

• Control joints introduced at ≤ 6.0–8.0 m (by wall type/height).
• Slab/soffit interfaces: backing rod + sealant at fire-rated conditions; galv. clips/angles at ceilings/edges as per detail sheets; deflection heads to maintain separation from moving structure.

5) Build sequence & workmanship

• First course set perfect to line/level; uniform joint thickness maintained.
• Units wetted before laying (prevent mortar suction); no smears/cracked arrises accepted.
• Raking out 12 mm where plaster is specified; wet curing 3 days to protect mortar.
• No chasing until walls gain strength; all MEP chases/boxes pre-marked from drawings. 

6) QA/QC & ITP hold-points

• Random block strength tests, mortar cube tests (7 day), and dimensional checks.
• IR inspections at first course, reinforcement/grout stages, pre-plaster, and completion; checklists signed by site/QC/consultant. 

What made the difference (selected technical details)

• Reinforcement tables by wall thickness/height guided where vertical bars and horizontal mesh were mandatory—avoiding over- or under-reinforcing panels. 
• Lintel schedules (with clear-span vs. depth combinations) standardised procurement and prevented site improvisation at openings. 
• Deflection head details (page sheets) separated the blockwork from beam/soffit movement, reducing cracking at the top course. 
• C24/30 grout with 10 mm aggregate ensured bar encapsulation and bond in hollow units and bond beams, improving shear transfer around openings and T/L-junctions. 

Results

• Zero rework at IR hold-points for first-course, reinforcement, and lintel stages.
• Crack-free finishes at handover (post-cure), attributed to control-joint spacing, mesh, and deflection heads.
• Clean MEP coordination—all boxes/chases landed on pre-marked positions, eliminating last-minute chasing.
• Programme certainty—repeatable wall bay modules (≈6 m) allowed parallel teams without quality drift. 

Lessons for live London projects

1. Start with the first course—it governs everything.
2. Engineer the openings (lintels, jamb bars, grout) early; it kills 80% of aesthetic defects later.
3. Treat the top course like a joint—deflection heads + fire stops = fewer claims.
4. QA cubes + random block tests are cheap insurance for client sign-off. 

FAQ quick notes (from our template)

• Can we chase blocks the same day? No—wait for strength gain; follow approved chase locations only.
• Why grout to C24/30 with 10 mm agg? To fully bond bars and lintels inside hollows/bond beams without segregation.
• Do we always need mesh every two courses? Where specified for crack control and as per height/thickness tables—yes.