What is a formwork spreader?
A formwork spreader is a distance piece wedged between two opposing formwork faces. It holds the shutters apart at the correct spacing, so the wall or column is cast at exactly the intended thickness.
Where the tie rods hold the formwork together against the pressure of wet concrete, the spreaders do the opposite: they stop the faces being pulled towards each other. The Dutch term for this component is pieleman.
How it works
The traditional version is a timber batten cut to exactly the wall thickness. It is placed when the formwork is closed and pulled out during the pour, as soon as the concrete reaches that level. Leave it in and you get a timber inclusion in the wall: a rot-prone spot, and in a water-retaining structure a leakage path.
In modern panel formwork the spreader has largely been replaced by conical spacer tubes around the tie rod. These take the compression, stay in the concrete and are sealed after striking with a concrete plug or sealing cone.
| Timber spreader (traditional) | Batten cut to exactly the wall thickness; placed when the formwork is closed and pulled out during the pour, as soon as the concrete reaches that level. |
|---|---|
| Conical spacer tube (modern panel formwork) | Sits around the tie rod and takes the compression; stays in the concrete and is sealed after striking with a concrete plug or sealing cone. |
Points to watch
- Accuracy is everything. A batten one millimetre too long shifts the whole wall. Cut them all to one gauge, not individually by eye.
- Pull them during the pour. Agree before pouring who removes the spreaders, and mark the positions at the top — otherwise they get forgotten.
- Not the same as a spacer. A rebar spacer holds the reinforcement away from the formwork and secures the concrete cover; a spreader holds the shutter faces apart.
- Water-retaining structures. In basement walls and tanks every continuous element is a potential leakage path. Use spacer tubes with a waterstop, or a system the supplier has approved for that application.
Related terms
- Formwork
- Spacer
- Concrete cover
- Tie rod
- Striking formwork
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