Reference
Construction terms, in plain English.
The words that turn up on quotes, engineers' drawings and strata reports, explained without the jargon that usually comes with them. If a contractor uses one of these and cannot explain it, that tells you something.
Concrete
Concrete terms
- Cover
- The depth of concrete between the reinforcing steel and the surface. Cover is what protects the steel from water and corrosion, which is why an engineer specifies it and why reinforcement gets sat on chairs rather than dropped on the ground.
- Spalling
- Concrete breaking away from the surface in flakes or chunks. In reinforced concrete it is almost always driven by the steel underneath corroding and expanding.
- Concrete cancer
- The common name for spalling caused by corroding reinforcement. Water and chlorides reach the steel, the steel rusts, the rust expands, and it pushes the concrete off from the inside.
- Drummy
- Concrete that sounds hollow when you tap it, meaning it has debonded from what is underneath. It is a common early sign of spalling, before anything has actually let go.
- Control joint
- A deliberate line of weakness cut or tooled into a slab so it cracks where you chose rather than where it decides. Concrete will crack; a control joint decides the location.
- Isolation joint
- A joint that separates a slab from a building, a pit or another slab so the two can move independently without cracking each other.
- Screed
- Levelling wet concrete to the correct height by drawing a straight edge across the forms. Also the name for the board itself.
- Curing
- Keeping fresh concrete damp or sealed for a period so it gains strength properly. Skipping it causes surface cracking and dusting that no later treatment recovers.
- Slump
- A measure of how wet and workable a concrete mix is. Adding water on site to make concrete easier to place raises the slump and lowers the final strength.
- Exposed aggregate
- A finish where the surface cement is washed back to reveal the stone in the mix. It hides marks well and grips better in the wet than a smooth finish.
- Bar chair
- A small plastic or steel support that holds reinforcement at the specified cover while the concrete is placed around it.
- Vapour barrier
- The plastic membrane laid under a slab to stop ground moisture rising through it. Punctures during construction defeat it.
- Reactive soil
- Clay that swells when wet and shrinks when dry, moving whatever sits on it. Much of Sydney is reactive, which is why slab design belongs to an engineer.
Carpentry
Carpentry terms
- Formwork
- The temporary mould that holds concrete in shape until it can support itself. The finished shape, level and surface of the concrete are all inherited from it.
- Falsework
- The temporary structure that supports formwork and the wet concrete load until the concrete has gained strength.
- Waler
- A horizontal member running across formwork studs to spread the load and keep the face straight under pressure.
- Snap tie
- A steel tie holding opposing form faces at the correct spacing during a pour. The ends snap off after stripping.
- Stripping
- Removing formwork once the concrete has enough strength to stand without it. Too early risks the concrete; too late damages the finish and holds up the programme.
- Set-out
- Marking positions and levels from the drawings before anything is built. Almost every expensive framing or formwork error traces back to set-out.
- Noggin
- A short piece of timber fixed horizontally between studs, used for bracing and to give later trades something to fix into.
- Tie-down
- The strap, bracket or bolt connecting a frame to the structure below so wind cannot lift it. Certifiers look for these specifically.
- Scarf joint
- An angled joint used to splice a new length of timber onto a sound existing member so the repair disappears once finished.
Guard rail
Guard rail terms
- MASH
- The Manual for Assessing Safety Hardware, the crash test standard road safety barriers are assessed against in Australia. Barriers are rated at test levels such as TL2, TL3 and TL4.
- Embedment depth
- How deep an anchor sits into the concrete. It is specified for a reason, and shortening it leaves a barrier that looks identical while performing at a fraction of its rating.
- Edge distance
- How far a fixing sits from the edge of the concrete. Drill too close to an edge and the concrete breaks out under impact instead of holding.
- Wheel stop
- A low block fixed to the ground that stops a vehicle over-running the end of a parking bay.
- Bollard
- A vertical post protecting something from vehicle impact. Its strength comes from the footing, not the post, so how it is fixed matters more than what it is made of.
- Rack protection
- Guards fitted to pallet racking uprights and row ends. A struck upright can compromise a whole run of racking and should not be reloaded until it has been assessed.
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