How to Schedule Formwork Cycles for Multi-Storey RC Builds

Why does formwork management cause so many delays on RC frame buildings?

For Thai SME contractors building multi-storey RC structures — shophouses, low-rise condos, apartment blocks, and small office buildings — the concrete frame is the longest single activity on the schedule. Columns, beams, and floor slabs repeat floor by floor, and the team that manages the rhythm of erect-pour-cure-strip-move controls the whole project. Yet on most small sites the formwork cycle is managed by feel rather than plan. The project manager knows roughly how long each floor takes, the foreman shifts the panels when the engineer says it is safe, and the schedule records a single activity labelled concrete structure running from mobilisation to frame completion. When one pour slips by two days — from rain, a pump breakdown, or a late rebar delivery — the floor cascade pushes out, and three weeks can vanish before the frame is halfway up.

What is a formwork cycle and why does it belong on the Gantt?

A formwork cycle is the repeating sequence of tasks needed to form, pour, cure, and reuse the shuttering for one floor of an RC building. A typical cycle has five phases: erect column forms and pour columns, wait for column concrete to reach striking strength, erect beam and slab soffit forms, pour slab and beams together, and cure the slab before stripping soffit forms and moving them to the next floor. The cycle time — the calendar days from column forming on floor N to column forming on floor N+1 — determines how quickly the building rises. On a Thai residential project with a standard 250-millimetre flat slab and one gang of formwork, that cycle typically runs nine to fourteen calendar days per floor, depending on temperature, water-cement ratio, the structural engineer's stripping criteria, and crew size. Planning this cycle explicitly on the Gantt planning view turns a vague activity into a predictable, floor-by-floor sequence that can be monitored and managed.

How do you plan a floor-by-floor formwork cycle in SiteBoard's Gantt?

In SiteBoard's Gantt planning view, build the formwork cycle as a group of linked tasks repeated for each floor. A minimal task set per floor includes column forming and rebar preparation, column pour and cure, soffit and beam form erection, slab reinforcement and MEP sleeve installation, slab pour, slab cure, and soffit strip and hoist to the next floor. Each task gets a duration based on crew size and specification requirements, and sequential dependencies link them so that adjusting the column cure duration on floor three automatically pushes every downstream task on that floor and every floor above it. Once the first-floor cycle is correct, replicate the task group for floors two through the roof and connect the start of each floor's column task to the soffit-strip finish on the floor below. The Gantt becomes an honest forecast of the roof slab date — not an optimistic single line.

What does a typical formwork cycle look like for a Thai shophouse?

On a five-storey RC shophouse in Bangkok with a four-metre floor-to-floor height and a 250-millimetre flat slab, a practical cycle with one set of column forms and one soffit panel set runs as follows. Day one to two: set column forms, tie rebar, pour columns. Days three to four: cure, achieve 70% design strength, strip column forms. Days three to eight: erect soffit props and beam and slab panels while columns cure. Day nine: install slab rebar and MEP sleeves. Day ten: pour slab and beams. Days eleven to fourteen: cure slab, crush test cubes, structural engineer authorises strip. Day fourteen to fifteen: strip soffit forms and crane or hoist to the next floor. Each floor thus takes fourteen to fifteen calendar days. For five storeys above ground, the frame takes roughly seventy to seventy-five calendar days — giving the project manager a reliable date to plan finishing trades entry.

A real example: a Nonthaburi five-storey build that lost eighteen days

A contractor in Nonthaburi built a five-storey RC apartment block at 14 million baht on a thirty-week programme. The Gantt showed a single structure task running sixteen weeks — no formwork cycle tasks were included. In week four, the rebar supplier delivered one floor late because the contractor had not factored lead time into the order schedule. This pushed the first-floor column pour by four days. Since soffit forms could not be erected until column concrete was struck, the first slab pour slipped to day nineteen instead of day ten. By floor three the delay had compounded to eleven days; by floor five, eighteen days. Finishing subcontractors contracted to start at week seventeen found the site not ready until week nineteen. The contractor paid two weeks of idle time to tiling and plastering crews and finished in week thirty-four — four weeks late on a programme that had looked achievable because the cycle had never been planned explicitly.

How do you decide how many sets of formwork to use?

The number of formwork sets on site determines whether work runs continuously or must wait for panels to complete one cycle before the next floor can start. With one set of soffit forms and a fourteen-day cycle, floor two cannot begin forming until floor one is stripped — a single-thread programme. With two sets, floor two forming can begin while floor one slab is still curing, overlapping by five to seven days and reducing total frame duration by roughly thirty percent. Whether the extra set is worthwhile depends on rental cost against saved site overheads. For a project where overheads run at 120,000 baht per week, cutting three weeks from the frame with a second form set at 25,000 baht per week rental pays back in under two weeks. Modelling both options in the Gantt planning view with two parallel floor sequences shows the exact overlap and gives the contractor a data point to use in the pre-construction meeting.

How do you track formwork progress floor by floor in SiteBoard?

Track each formwork task as an on-site progress update in SiteBoard. When column forms are erected and rebar is tied, update the column task to 100% and attach a photo of the form set. When the pour is complete, note the pour date, volume pumped, and slump test result. When the structural engineer confirms stripping strength from test cube results, update the cure task to 100% and record the cube result and authorisation to strip. This builds a floor-by-floor record that, if a dispute arises over delay to finishing trades, proves exactly when each floor was structurally ready. Owners with access to the owner sharing link can see which floor's slab has been poured without calling the site — a simple way to manage the expectations of an owner funding the build by bank instalment.

What is backpropping and when does it matter on Thai sites?

Backpropping means leaving temporary props under a previously stripped slab to support it while the floor above is poured. When a slab is stripped at around seventy percent strength and the floor above is immediately poured, the weight of fresh concrete, formwork, and crew transfers to the slab below, which is still gaining strength. On a flat-plate RC system without backpropping, this can cause excessive deflection in the slab below. Thai structural engineers typically specify backpropping for at least one floor below the active pour. In practice, backpropping is often omitted on small sites because the team needs the props for the floor above. In the Gantt planning view, model backpropping as a task on the floor below with a duration spanning from the slab strip to the completion of the floor above — this keeps the props on the schedule where they can be tracked.

FAQ: How long should a contractor wait before stripping soffit formwork?

The minimum wait depends on concrete grade, ambient temperature, and the structural engineer's specification. Thai structural engineers commonly require test cube results showing seventy to eighty percent of design compressive strength before authorising soffit strip, typically verified by seven-day cube crushing. Under typical Bangkok conditions with Grade 280 concrete at 32 degrees Celsius, seven-day cube results are often sufficient for a standard flat slab. In cooler upcountry conditions or for heavily loaded spans, the engineer may require ten to fourteen days. The correct approach is to ask the structural engineer for a written stripping criterion at the pre-construction meeting and record the cube results and strip authorisation as on-site progress updates in SiteBoard, so the record exists if structural performance is questioned after handover.

FAQ: When does the formwork cycle become the critical path?

The formwork cycle becomes the critical path — the longest unbroken chain that controls the project finish date — on virtually every new-build RC frame project from mobilisation until the roof slab is complete. Any slip in the cycle directly delays the earliest possible start for plastering, screeding, and MEP first fix, since those trades cannot enter a level until the floor above has been poured and the working level is structurally safe. In SiteBoard's Gantt planning view, a correctly built cycle with sequential dependencies automatically highlights this: any extension to a critical task moves the project end date, giving the project manager an early warning while there is still time to add crew or schedule a weekend pour to recover.

FAQ: Can RC frame construction and finishing trades run in parallel?

On buildings of five floors and above, finishing trades on the lower floors can run in parallel with frame construction on the upper floors, with at least two floors of vertical separation to account for falling debris, vibrator vibration, and curing water. A contractor building a five-storey block can typically begin first-fix plumbing and electrical roughing-in on floor one while pouring the slab on floor three, provided the structural engineer confirms loading is safe and the site supervisor manages zone separation. Planning this overlap in the Gantt planning view — with a two-floor buffer dependency linking the start of finishing trades on floor N to the completion of the slab pour on floor N+2 — turns an informal site call into a scheduled, owner-visible programme.