A formwork base anchor is a spacer for wall formwork that is pushed into still-fresh concrete at the kicker position — where the wall meets the floor slab. Once the concrete has hardened the anchor is locked in place and forms the starting point that both formwork panels are clamped against. The bottom of the wall formwork is then immediately at the correct spacing: the wall thickness.
How it is built up
Such an anchor usually has three parts:
| Part | Function |
|---|---|
| The anchor | A vertical element with a corrugated or ribbed profile that is pressed into the fresh concrete and grips in it |
| Threaded rod | Lets you set the spacing exactly |
| Caps | Usually plastic end pieces on the rod, which the formwork bears against |
The caps can be rotating or sliding, so the dimension can be trimmed to the millimetre. For heavy formwork two anchors are sometimes combined, or pre-assembled versions used.
Where it is used
Base anchors are mainly used in in-situ concrete construction: house and apartment shells poured with wall or tunnel formwork. They are an alternative to a cast kicker: instead of first pouring a low upstand for the wall formwork to clamp against, you set the formwork against the anchors.
Practical points
- Set them immediately after pouring — the anchor has to go into concrete that is still plastic; leave it too long and it sits loose or tears the concrete
- Stop them sinking — flat, corrugated anchors sink less readily than round ones; a plastic setting plate under the anchor helps in a soft mix
- Check the dimension before pouring the wall — measure the centre spacing and wall thickness at several points; an error at the base runs through the full height of the wall
- Slab flatness — a base anchor corrects the wall thickness, not the level of an uneven slab; check that separately with a laser
- Leftovers — plastic caps and threaded rods stay in or just below the concrete surface; remove protruding parts before screeding or plastering
Related terms
- Kicker formwork
- Wall-floor joint
- Formwork
- In-situ concrete
- Concrete floor
- Reinforcement
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