Most construction defects are visible and correctable right up until the moment they are cast in. After that they are structural, hidden, and expensive in a way that has nothing to do with the cost of fixing them - because reaching them means breaking something that is now holding a building up.
This is the single highest-value hour a client can spend on site, and it needs no technical training to be useful.
Why this hour matters
A pour is irreversible. There is no stage later in the job where the reinforcement can be adjusted, the cover increased, or the slab brought back to level. Every trade that follows inherits whatever the pour leaves, which is why a slab that is out of level turns into a flooring problem, a door height problem and finally a complaint about the building.
If a pour is running late and someone suggests checking afterwards, that is the moment to stop. Afterwards does not exist for any of this.
Reinforcement
The steel should match the drawing, and the drawing should be on site. Checking it is mostly a matter of looking.
- Bar diameter and count Against the bar bending schedule, not against what looks reasonable. A missing bar in a beam is not visible once the shutter is filled.
- Spacing Even, and at the spacing given. Bars that have drifted during tying are common and easy to correct while they are still exposed.
- Laps In the right places and of the right length. Laps clustered at a point of high stress are a design problem someone has introduced on site.
- Binding Tied firmly enough that the cage does not move when someone walks on it during the pour - because someone will.
- Cleanliness Free of loose rust, oil and mud. Concrete has to grip the bar for any of this to work.
Cover
Cover is the distance between the steel and the outside face of the concrete, and inadequate cover is the most common buildable defect in Indian construction. It is also the easiest to check and the easiest to fix - in the ten minutes before a pour, and never again.
Cover blocks hold the bars off the shutter at the specified distance. They should be present, of the right thickness, at the spacing the drawing gives, and under the bars rather than pushed aside. Steel sitting directly on the shutter has zero cover at that point, and that is the point where water will reach it.
What is at stake is time, not appearance. Reinforcement with proper cover is protected by the alkalinity of the concrete around it. Reinforcement without it corrodes, and corroding steel expands and cracks the concrete that was meant to protect it. That process shows up as spalling years later, and by then the repair is structural.
Shuttering and level
- Shutters tight at every joint. An open joint leaks the cement paste out and leaves honeycombing behind it - visible only when the shutter comes off.
- Props and staging adequate and on a firm base, checked under load rather than assumed.
- Shutter faces clean and correctly oiled, so the shutter releases without pulling the surface with it.
- Level and line checked and recorded before the pour, not corrected after.
- Openings, sleeves and conduit boxes in place. Cutting a hole through a finished slab for a pipe somebody forgot is expensive and weakens it.
The concrete itself
The grade should be what the structural design calls for. The thing worth checking is whether what arrives is what was specified.
- The delivery record For ready-mix, the docket states grade, batch time and quantity. It is worth reading rather than filing.
- Time since batching Concrete has a working life. Material that has been in traffic too long should not be improved by adding water at the gate - which is the usual temptation and ruins the strength.
- Slump Tested on site, against what the mix design allows. A slump that has been adjusted upward with water is weaker concrete, whatever the docket says.
- Cubes Cast from the actual pour, marked, and tested at the agreed ages. Cube results are the only independent evidence of what was placed, and they are worth having before the next floor goes on top of it.
During and after the pour
Two things continue to matter once concrete is going in.
Compaction: the mix has to be vibrated enough to expel trapped air without being over-vibrated into segregation. Under-compacted concrete is porous, and porous concrete is how water reaches the steel.
Curing: concrete gains most of its strength in the first fortnight and only while it stays wet. Curing that gets shortened to recover programme is the cheapest possible saving on a site and reliably the most expensive one later. It is worth agreeing the curing period before it becomes the thing standing between the job and the next floor.