A fixing block — the Dutch klis or klisje — is a small timber block nailed to a floor or joist that serves as an anchor point for braces. A typical block measures about 30 by 100 mm; for heavier bracing, longer pieces up to 400 or 500 mm are used.
The block is a classic piece of carcass-stage kit. Anyone who has to hold a frame, a profile or a partition plumb until it is fixed needs a solid point at the foot of the brace: something that will not give, that you can push against or screw to. A brace standing only against a smooth concrete slab slides away — the block stops exactly that.
Where it applies
- Setting door and window frames — the braces that hold a frame plumb and square until it is fixed push off blocks on the floor
- Setting out corner profiles for brickwork — the profiles are strutted against blocks
- Temporary propping of walls and formwork — the block gives the strut purchase in a direction where it would otherwise slip
- Scaffolding and temporary works — as a stop or guide
Fixing it down
Traditionally a block is fixed with hardened steel nails — the Dutch klisnagel, a twisted concrete nail — into a timber joist or a concrete slab. In concrete a pilot hole is drilled first; because the nail is slightly twisted it grips in the hole. These days it is just as common to use an offcut of plywood fixed with a hammer-in anchor or a concrete screw.
Practical tips
- Choose the position deliberately — a block on a screed that will later be ground or coated leaves holes behind; put them where the finish will cover them
- Remove them completely — leave no nails or timber in a floor that still has to receive screed or insulation; a protruding nail will pierce a vapour control layer
- No structural load — a fixing block is a temporary aid; do not hang any structural load from it
- Work in two directions — always use at least two braces at an angle to one another; a single brace holds nothing
- Use dry timber — a block that twists leaves your carefully plumbed frame loose again a day later
Related terms
- Cleat
- Spiral concrete nail
- Formwork
- Door frame
- Screed
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