Concrete Curing: The Schedule Buffer Thai Contractors Miss

Why does a project stall right after a concrete pour even when the Gantt showed everything on track?

A contractor lays out the Gantt, assigns the concrete pour for week three, and schedules the block-wall crew to follow two days later. The pour goes perfectly. The crew shows up on day three. But the columns are not ready for load — the concrete has not reached anywhere near working strength. In Thai heat, concrete feels hard on the surface within hours, but surface hardness is not structural strength. A column loaded too early can settle slightly, creating hairline cracks at the connection to the beam above that are invisible and costly to address later. The concrete pour task appears complete on the schedule, but the curing period — the wait the Gantt never showed — is where the project quietly falls behind when the next trade cannot actually start on time.

What are the standard curing times for structural concrete in Thai residential construction?

Vertical formwork on columns and walls can typically be stripped after 24 to 48 hours for standard mix designs. But stripping formwork does not mean the concrete is ready for load. Structural engineers generally use 7-day compressive strength as the threshold for applying construction loads — at this point concrete typically reaches about 70 percent of its 28-day design strength. For slabs, soffit formwork and temporary props should remain for a minimum of 14 days for spans up to 4 metres, and longer for larger spans, unless a cube test confirms earlier stripping is safe. In Thailand's climate, high temperatures accelerate the initial set but can cause rapid surface drying that reduces final strength if the concrete is not kept moist. Never remove slab props based on surface feel alone.

How do you add a curing buffer as a task in the Gantt planning view?

After each pour task in the Gantt planning view, create a task labelled Cure followed by the element name — for example, Cure: ground floor columns, or Cure: first floor slab. Set its duration to the appropriate curing period: 7 days for columns before adjacent block work begins, 14 to 21 days for slabs before soffit props are stripped. Link the pour task as a predecessor to the cure task, and link the cure task as a predecessor to the first following trade. The chain reads: pour then cure then next trade starts. When the pour date shifts, the cure end date and the next trade's start date move automatically in the Gantt planning view, without any manual recalculation needed.

Which concrete elements need the longest curing buffers in a typical Thai house build?

Slabs and beams carry the greatest curing risk because soffit props support live load from above and must remain until concrete reaches sufficient strength. A 200mm-thick slab spanning 4 metres needs a minimum of 14 days before soffit props can be removed; larger spans and two-way slabs often need 21 days. Ground and upper floor beams follow the same rule as slabs. Columns and walls, once stripped of vertical formwork, need 7 days before the adjacent block walls place sustained load on them. Footings and pile caps need at least 7 days before the column reinforcement above is loaded. Naming all four curing periods as tasks in the Gantt planning view at the start of the project creates a realistic programme from day one.

A worked example: a two-storey house in Nonthaburi that lost three weeks by skipping the curing buffer

Khun Prasit was managing a new two-storey house in Nonthaburi worth 2.8 million baht on a 16-week programme. The Gantt showed column pours in week four and block-wall laying starting in week five. The pour finished on Thursday afternoon. The block-wall crew arrived the following Monday — three days later. By Thursday of week five, the site inspector noticed hairline cracks at the column-to-beam joint on the north corner. The block load had been applied before the columns reached 7-day strength. The block work on that wall had to be taken down, the column crack assessed, and the work rebuilt — a cost of 38,000 baht and three weeks added to the programme. A seven-day cure task between the pour and block-work start in the Gantt planning view would have sent that crew to a different section of the site for the week and avoided the loss entirely.

How do curing tasks on the owner sharing link prevent anxiety during quiet periods on site?

An owner who visits the site during a curing period and sees no trade activity often concludes that work has stopped or the contractor is behind. This can damage trust even when the contractor is doing exactly the right thing. When the Gantt shared through the owner sharing link in SiteBoard includes the curing tasks with their scheduled durations, the owner sees that the quiet period is planned — a task named Cure: first floor slab is currently active and ends on Sunday. There is nothing wrong; the programme is running correctly. As the foreman logs each day of the curing period through the on-site progress updates feature, the owner watches progress tick forward even on days when no block is laid and no tile is cut.

Managing multiple concrete pours across floors or phases without leaving trades idle

On a multi-storey build, each slab pour creates a curing window of two to three weeks. A contractor who plans only one active section at a time will have the formwork crew idle while waiting for the previous slab to cure. The solution is to stagger pours: while the ground floor slab is curing, the formwork crew erects the next floor's shuttering in a section where no fresh concrete is below. In the Gantt planning view, each pour is a separate task with its own cure task. Overlapping the formwork erection task on section two with the cure task on section one keeps the formwork crew continuously productive and compresses the overall structural frame programme by weeks on a three or four-storey build.

FAQ: Can you strip slab formwork before 14 days in Thailand where heat accelerates setting?

Vertical formwork on columns and walls — yes, stripping at 24 to 48 hours is standard practice for most mix designs. Soffit formwork under slabs and beams — only with structural engineer confirmation from a cube test result. Thailand's high daytime temperatures do accelerate early setting, but they also increase the risk of surface drying that reduces final compressive strength if curing compound or wet curing is not applied. Never strip slab props based on how hard the surface feels. If a cube test at 7 days confirms sufficient strength, mark the cure task complete in the Gantt planning view on that day and proceed. Log the test result date in the task notes as a record for the project file.

FAQ: How does a linked curing task handle a late concrete delivery automatically in the Gantt?

If the concrete truck is delayed and the pour happens two days later than planned, mark the pour task with its actual start date in the Gantt planning view. Because the cure task and all downstream tasks are linked as predecessors, their dates shift by the same two days automatically. The contractor can immediately see whether the late pour affects the project completion date or only consumes a float buffer. Without a linked cure task, a late pour is often recorded only in the pour task while the next trade's start date stays unchanged — so the crew is still scheduled to arrive before the concrete is ready, and the conflict only becomes visible on site when it is too late to redirect them.

FAQ: How do you use on-site progress updates to document a concrete curing period in SiteBoard?

Treat the cure task like any other site task in the on-site progress updates feature. The foreman updates the curing task's percentage complete each day — Day 1 of a 7-day cure is roughly 14 percent, Day 7 is 100 percent. In the note field, record the pour date, the concrete grade, and the supplier name. Attach a photo of the fresh pour as the first update and a photo of the stripped formwork when the task closes. This creates a time-stamped record inside SiteBoard documenting when the pour happened, how long the cure ran, and when the next trade was cleared to begin — available months later if the structural engineer or the owner asks for evidence of the construction sequence.