A concrete column is poured once and stays for the life of the building, and the formwork it was cast in decides its shape, alignment and surface. A column a few centimetres out of plumb, bulging in the middle or full of voids is very hard to correct once the concrete has set. This guide explains how column formwork should be fixed and checked, and what an owner should look for before, during and after the pour.
What column formwork does, and why it matters
Formwork (often called farma on Saudi sites) is the temporary timber or steel mould that holds fresh concrete around the reinforcement until it hardens. It is stripped and reused, but its quality shows in everything built afterwards:
- A column out of plumb shifts beam lines, leaves adjacent walls crooked and needs thicker plaster to hide the lean.
- A bulging column means the formwork could not resist the concrete pressure, leaving an uneven surface.
- Honeycombing – voids and exposed aggregate – can expose the steel to corrosion.
- A column off its grid line changes the load path the engineer designed and can clash with door and window positions.
That is why we treat column formwork as one of the most sensitive steps in structural skeleton works, even though it looks like simple boards and clamps.
Types of column formwork
| Type | Main advantages | Watch out for |
|---|---|---|
| Timber / plywood | Flexible for any size, widely available | Worn boards, open joints, weak clamping |
| Steel | Smoother finish, accurate sizes | Cleaning, oiling, limited standard sizes |
| Ready-made round moulds | Clean, regular circular columns | Bracing and plumb checks as for any column |
Timber and plywood remain the most common on villa projects in Riyadh. Steel forms suit projects where the same column size repeats many times.
What must be ready before the formwork closes
Once the boards are fixed, nobody sees the steel again. Check these first:
- Setting out – each column is located from fixed reference points on site, not just measured from the neighbouring column, so errors do not accumulate along a row.
- Reinforcement – bar count, diameters and links (stirrups) as per the structural drawing, including any closer link spacing the engineer specifies at the top and bottom.
- Lap length – the overlap with the starter bars from the column neck or the slab below.
- Spacers – concrete or plastic spacers tied to the bars to guarantee concrete cover. The engineer sets the value; around 40 mm is common for columns, but the drawing and specification are what count.
- A clean base – no soil, timber offcuts or wire at the foot of the column, and the old concrete surface prepared as the engineer directs.
Fixing and plumbing the formwork
Preparing the boards
Boards are cut to the exact column size and given a thin, even coat of release oil. Too much oil stains the concrete, and oil must never reach the reinforcement because it weakens the bond.
Clamping
The sides are fixed at the base on the marked grid line, then clamps or yokes are fitted at regular spacing. Fresh concrete pushes hardest at the bottom, so clamps are closer together there. Joints between boards are sealed so that cement paste cannot leak out – leaking paste is a leading cause of honeycombed corners.
Setting plumb
This is the step that separates careful work from rushed work. The column is plumbed on two faces at right angles with a plumb bob, then braced with diagonal props in at least two directions. On long rows of columns, a survey instrument keeps them in line. A short spirit level is not enough on its own: a tiny error over its length multiplies over the height of the column.
Final checks before the pour
- Internal dimensions match the drawing at the top and bottom.
- Diagonals are equal on square and rectangular columns.
- The top-of-pour level is clearly marked.
- Props bear on firm ground, not loose fill.
During the pour
- Place concrete in layers and vibrate each one, without over-vibrating in one spot or leaning the poker on the formwork.
- Avoid dropping concrete from a height; the pump hose or a chute keeps aggregate from separating.
- Assign someone to watch the formwork for bulging, leaks or moving props.
- Recheck plumb during the pour, as vibration can nudge the formwork.
- Never add water on site to make concrete flow easier. If the mix is wrong, that is the engineer’s call.
In summer these details matter even more – see pouring and curing concrete in Riyadh heat.
After the pour
Plumb is checked again straight after the pour, while small corrections are still possible by adjusting the props. The engineer then decides when to strike the formwork; striking too early breaks the arrises, and levering boards off damages the face. Inspect the column right away for honeycombing, exposed steel or spacers, and uneven surfaces, and refer any defect to the engineer. Hiding defects under plaster is a common mistake that returns later as rust stains or cracks. Finally, columns need curing too – wrapping them in wet hessian or polythene keeps them moist in the first days.
Common defects at a glance
| Defect | Likely cause | Prevention |
|---|---|---|
| Honeycombing | Poor vibration, paste leaking at joints | Layered pour, steady vibration, sealed joints |
| Lean | Weak bracing, no plumb checks | Props in two directions, checks before and after |
| Bulging | Clamps too far apart, weak boards | Closer clamps at the base, sound boards |
| Exposed steel or rust spots | Missing or displaced spacers | Enough spacers, tied firmly |
| Off grid | Setting out from the next column | Set out from fixed reference points |
Questions to ask your contractor
- How do you set plumb, and when do you recheck it?
- Does the engineer inspect steel and spacers before the formwork closes?
- Is someone watching the formwork during the pour?
- What happens if honeycombing appears after striking?
- Can you send photos of the steel before closing and of the columns after striking?
Clear answers are a sign of good site supervision.
How Marafi handles column formwork
At Marafi we fix column formwork with the highest precision and check it for plumb before and after the pour, because a straight column is the base for every beam, slab, wall and finish above it. We follow the engineering drawings strictly for column sizes, reinforcement and positions, and a team of labourers, technicians, supervisors and engineers follows every pour under strict safety standards. Owners receive photos at each key stage. See Structural Skeleton Works, Reinforced Concrete Works and our process on How we build.
Quick checklist
- Columns set out from fixed reference points.
- Steel, links and laps checked against the drawing.
- Spacers fixed for concrete cover.
- Sound boards, light oil, sealed joints.
- Clamps closer at the base; props in two directions.
- Plumb checked before, during and after the pour.
- Layered pour with vibration, no added water.
- Surface inspected after striking, then cured.
Straight columns also make plastering easier, as our plastering quality checklist shows. Planning to build in Riyadh? Contact us to arrange a site visit and drawing review, and we will send an itemised proposal by stage.
Frequently asked questions
What does it mean for a column to be plumb?
A plumb column is truly vertical in both directions. It is set with a plumb bob or survey instrument before the pour, then rechecked during and immediately after it.
When can column formwork be removed?
The engineer sets the striking time based on temperature, cement type and mix. Columns are usually struck earlier than slab formwork, but striking too early can damage edges and the surface.
What causes honeycombing in columns?
Usually poor vibration, cement paste leaking through formwork joints, or congested reinforcement with an unsuitable mix. Repairs should follow the engineer’s instructions, not be hidden under plaster.
Does a slightly leaning column matter?
A visible lean may change how loads are carried and needs an engineering assessment. Even a small lean means thicker plaster and awkward doors, windows and tiling around the column later.
