A spiral concrete nail — the Dutch klisnagel — is a nail used to fix a fixing block or cleat: the small timber block on a floor or joist that gives braces something to push against. It is struck from hardened steel and has a slightly twisted or fluted shank; that twist makes it lock into the drilled hole, so the block sits rock-solid on the concrete.
A common size is around 4.5 × 40 mm. In concrete you drill a pilot hole of about 4 mm first — deliberately tight against the nail diameter — and then drive the nail home. In timber it can usually be driven without a pilot hole, though drilling avoids splitting near an end grain.
Where it applies
- Fixing timber blocks to a concrete slab when setting frames, profiles and partitions
- Temporarily fixing cleats and stops in carcass and formwork work
- Battens and grounds on concrete or masonry where a resin anchor would be overkill
- Scaffolding and temporary works that will be taken down again
Practical tips
- Drill tight — an oversized hole means the nail will not grip; follow the drill size the supplier specifies and err half a millimetre small rather than large
- Two nails per block — with a single nail the block simply rotates as soon as it takes a sideways force
- Not into prestressed floors — never drive blind into hollow-core or lattice-girder slabs; you will hit strands or reinforcement. Check the floor build-up first
- Wear eye protection — hardened nails can spring back or splinter on a mis-hit; safety glasses are not optional here
- Removing them — draw the nail with a pry bar over a block of timber so you do not damage the floor, and leave no heads standing where insulation or membrane still has to go
- Alternative — where the block has to stay longer or take more load, a hammer-in anchor or a concrete screw is more reliable than a nail
Related terms
- Fixing block
- Cleat
- Concrete
- Anchor
- Screed
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