Three operations repeated on every floor
A house's concrete frame is built in a three-step cycle: formwork, reinforcement, pour. The cycle repeats on every level, from the slab above the foundations to the roof if it is concrete. There is a pause between cycles: the concrete gains strength, and only then is the formwork struck and the slab loaded with the next floor.
For the owner this is the most visible stage. The foundations are barely seen, but now columns, slabs and stair flights appear week by week, and the house shows its real volume for the first time. It is exactly when many clients first understand how the living room will feel or what the bedroom view will be, and want to change something. Below is what can still change at this point, and what cannot.
Formwork: the shape of the house in timber and steel
Formwork sets the geometry: column sections, slab depth, balcony edges, stair openings and service shafts. A mistake here is cast in concrete for good. So before the reinforcement goes in, levels, column plumb and opening sizes are checked against the drawings.
If you want exposed concrete, say a living room ceiling with no plaster, that is decided before the formwork goes up. Architectural concrete needs different panels, careful joints and an agreement in advance on which marks are acceptable. Saying 'let's leave it as it is' after striking an ordinary slab usually ends with a surface that has to be covered anyway.
Reinforcement and the pre-pour check
Reinforcement is laid to the engineer's calculation: bar diameters, spacing, anchorage and the concrete cover over the steel. Before every pour, the responsible technician checks that what is on site matches the drawings, not the crew's habits. It is one of the key checkpoints of the whole build, because once the concrete is in, the steel is out of sight.
At the same moment sleeves and cast-in items are checked: openings in the slabs for drainage, ventilation, air-conditioning ducts, or feeds for terrace lighting. Every opening forgotten before the pour has to be cored through finished concrete later, and the engineer will not allow that everywhere. That is why service routes must be agreed before the frame starts, not afterwards.
Pouring and curing
Concrete arrives in mixer trucks and is placed by pump. Each delivery note is checked against the concrete class ordered, and a laboratory takes test samples, which is how you verify that the house got the concrete the project specified. Control requirements are set by the Código Estructural.
Curing starts once the pour is done. In summer in Barcelona and along the coast the slab is kept damp and shielded from sun and wind so the surface does not dry too fast and crack. In rain the pour is postponed or protected. When formwork comes off and when the slab can take load is decided by the technician based on the element and the weather, not by the crew's gut feeling.
What the owner can still change at this stage
Before a particular slab is poured you can still move an opening, add a sleeve for a future route or change a feed for an outdoor light. Afterwards, almost nothing without the engineer. Partitions, finishes, most of the services and even some windows in blockwork walls are still to come, and those are easier to change.
So it pays to visit the site before each pour with the project lead and walk through the drawings: where the kitchen goes, where the level-access shower goes, where the air conditioning sits. A question asked the day before the pour costs a few minutes. The same question a month later costs diamond coring, a call to the engineer and a week's delay.
How it went on our house with a pool
From 2022 to 2024 we ran a detached house with a pool from start to finish, including solar panels on the roof. The panels, their fixings and the cable route down to the plant room had to be planned at the frame stage, so we would not have to puncture the finished roof and its waterproofing later. It is a good example of why services are agreed before the concrete.
If you are building a house in Barcelona, the Garraf or the Maresme, we run the project with one person in charge, in Spanish or Russian, with stage payments under the contract. Send us the project or the plot and we will reply within an hour.