String line: the set-out reference line
A string line is a taut line stretched between two points to mark and check alignment and level. Why tension matters, and how it differs from a chalk line.
Ask Chalkline about this →A string line is a taut line stretched between two reference points to mark or check a straight line, an alignment, or a level on site. It is the simplest set-out tool there is, a length of line and two anchors, and it is on every job from the first peg to the last course of brick.
What it is for
A string line gives a physical straight edge in space that trades work to:
- Slab edges and footings: the line off the profile boards sets the edge of the slab or the footing trench.
- Brickwork: the brickie’s line, hooked on line blocks or pins, keeps each course straight and level, and the bed height consistent.
- Framing: a line along a wall plate or a row of stumps checks the run is straight before fixing.
- Fencing, paving, retaining: posts, pavers, and wall units are aligned to the line.
Because it can be re-strung at any time, it is also a check tool: stretch it along a finished run to see the bow or kick in it.
Tension is the whole point
A string line is only true if it is taut. A sagging line dips in the middle, so anything aligned to it follows a curve, not a straight line. The longer the run, the more a slack line sags under its own weight, and the more it matters.
Practical points:
- Pull it tight and anchor it so it cannot creep loose.
- Keep it clear of obstructions. If the line rests against a peg, a brick, or a clod mid-run, it is pushed off the true line at that point.
- On long or windy runs, support or re-tension it; wind bows a line sideways.
- Use good braided line that does not stretch or kink; a stretched, knotted line will not pull straight.
Not a chalk line
A string line and a chalk line are different tools:
- A string line marks a line in space, a reference you build to or measure from.
- A chalk line (a reel of chalk-coated string) is snapped against a surface to leave a chalk mark on it, transferring a position onto a slab, sheet, or wall.
One holds a line in the air to work to; the other prints a line onto a face.
For a builder
- Check the sag before you trust it. Sight down a long line; if it dips, re-tension before anyone works to it.
- Mind what it touches. A line brushing a peg or a high spot reads false exactly there. Keep the run clean.
- Offset lines are common. A line is often run a set distance off the true face (off the profile mark) so the work does not foul it; know the offset before you measure from it.
- It is a reference, not the mark. For a line that has to stay on the surface, snap a chalk line; the string line is for working to, then it comes down.
Also known as: stringline, builder’s line, brickie’s line.
Related
See also
Last updated: 2026-05-25. Verified: 2026-05-25. Quarterly review for currency.