A biljoen is a short, heavy timber post used as temporary support during foundation work or formwork construction. These sturdy posts carry loads for a limited period while permanent structural elements are being built, cast or cured.
Purpose and placement
In Dutch construction practice, the biljoen serves as a vertical prop that transfers the weight of freshly poured concrete, beams or floor sections down to a stable bearing surface. During foundation work, biljoens are driven or placed on compacted ground to support formwork panels and horizontal walers until the concrete has reached sufficient strength to carry itself.
The posts are typically made from hardwood or heavy-duty softwood, cut to precise lengths that match the required support height. On larger projects, steel props or adjustable shoring towers may replace timber biljoens, but on smaller and traditional building sites the timber version remains common because it is inexpensive, easy to cut to length on site, and reusable for multiple pours.
Use in formwork construction
When building formwork for concrete walls, columns or slabs, biljoens are positioned at regular intervals to prevent the formwork from deflecting or collapsing under the weight and hydraulic pressure of wet concrete. The spacing depends on the thickness of the pour and the stiffness of the formwork panels. Once the concrete has hardened and gained enough strength, usually after several days to a few weeks depending on conditions, the biljoens and the rest of the formwork are carefully removed in a process called stripping.
Practical considerations
Each biljoen must rest on a solid base, such as a sole plate or compacted gravel, to prevent it from sinking into soft ground. The top of the post should be fitted snugly against the formwork or beam it supports, sometimes with a wedge to allow fine height adjustment. Inspecting biljoens during a pour is important, because even slight settlement can cause formwork misalignment or cracking in the finished concrete.
Related terms
- Foundation
- Formwork
- Prop
- Pier
- Pile
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