Flexbox

Construx Precast designed a new type of adjustable moulds to produce any type of shaft or core without ties through the concrete element. The Flexbox system by Construx Precast is a revolutionary adjustable formwork solution designed to produce lift shafts, stair cores, and box culverts with fair-faced, watertight concrete surfaces - without ties through the concrete element. Its modular design allows for complete flexibility in size and application, making it ideal for high-precision precast production environments.

No through-ties – smooth, watertight results

Unlike traditional shaft moulds, Flexbox eliminates the need for internal tie-rods, resulting in:

• Clean, fair-faced surfaces
• Zero visible tie holes
• Improved watertightness

Connections are made only:

• At the base with spindles
• At the top with external tie-rods

How it works: modular & adjustable configuration

Adjustable base frame

• The system begins with a robust steel base frame
• All mould components lock into position on this base

Inner mould with hydraulic corners

• 4 retractable corners, hydraulically operated
• Without infill panels, they form the minimum shaft size
  • Common base sizes: 1200×1200mm, 1000×1000mm, or 900×900mm
• Add infill panels for custom sizes
  • Adjust in increments of 250mm, 10mm, or any value in between
• Corner profiles:
  • 90° angle (for shafts and stair cores)
  • Triangular chamfer (for box culverts)
  • Hybrid with detachable tops for dual-purpose use

Corners can be controlled via:

• Four hydraulic hand pumps or
• One central hydraulic unit

Wall thickness & base options

After positioning the inside mould:

• Steel base panels are mounted and height-adjusted
• Bases come in various widths to support different wall thicknesses
• Flat base: for lift shafts or stair cores
• Rebate base: for box culverts

A continuous height-adjustment system ensures concrete finishing is always flush with the mould top.

Outside panel configuration

• Outside panels connect in a hit-and-miss layout
• Allows for any external mould size, independent of inner mould dimensions
• Connects to the inner mould with spindles at the base and tie-rods at the top

Key benefits

• No through-ties = fair-faced, watertight concrete finish
• Highly adjustable dimensions in all directions
• One system for lift shafts, stair cores, and box culverts
• Modular corner options (90°, chamfered, hybrid)
• Fast setup and flexible reconfiguration
• Compatible with multiple wall thicknesses and base profiles

Typical applications

• Single, double, or triple lift shafts
• Stair cores with or without rebates
• Precast box culverts with precise angles
• High-performance solutions for infrastructure, residential, and commercial projects