How to Level a Concrete Floor With a Laser Level

A concrete floor that's out of level causes problems for every trade that follows — door frames that won't sit square, tiles that lip, screeds that vary in depth and racking that rocks. Whether you're pouring a new slab, laying a screed or levelling an existing floor with a self-levelling compound, a laser level takes the guesswork out of the job. Here's how to do it properly, the way it's done on site.

What You'll Need

• A rotary laser level with a receiver (detector) — for anything bigger than a single small room
• A sturdy tripod set on firm ground, away from the pour
• A levelling staff or a receiver mounted on a grade rod
• Marker pens, pins or screed rails, and a surveyors' tape measure for setting out
• A digital spirit level for checking rails and small areas

For small indoor rooms, a green-beam line laser such as a multi-line 4D laser will do the job without a receiver, but on larger floors a rotary laser is faster and far more accurate over distance.

Step 1: Set Up the Laser and Establish a Datum

Set the tripod on solid ground where the laser won't be knocked, out of the path of barrows and mixers. Mount the laser, switch it on and let it self-level. Then establish a datum — a fixed reference height that everything else is measured from. On most jobs this is a mark on a wall, column or peg at a known height, typically 1m above finished floor level (FFL). If you're not sure how to do this, our guide on setting a datum point on site covers it in detail.

Step 2: Survey the Existing Floor

Before you pour anything, find out what you're working with. Walk the floor on a grid — every metre or so on a small room, every 2–3m on a big slab — holding the staff or grade rod on the floor at each point. Read the height at each position and write it down or mark it on the floor.

The lowest point tells you your maximum depth; the highest point tells you your minimum. This matters because most self-levelling compounds have a minimum and maximum depth, and a screed needs a consistent thickness to cure properly. If the difference between high and low spots is bigger than your product allows, you may need to grind high spots or do the job in two passes.

Step 3: Mark Your Finished Floor Level

Working from your datum, measure down to your finished floor level and transfer that height around the room. With a rotary laser you can do this anywhere in the space in seconds: set the receiver to the FFL height on the rod, then mark walls, set pins or adjust screed rails until each one reads on-grade.

For a screed, set screed rails or wet screed dots at FFL using the laser, checking each with the receiver before the mix goes down. For a slab pour, set pins on your grid with the tops at FFL — the concrete gets tamped level to the pin tops.

Step 4: Pour and Check As You Go

Don't wait until the end to find out you're low. As the concrete or compound goes down, keep checking with the receiver on the rod. A second pair of hands helps here: one person rakes and tamps, the other checks levels and calls out high and low. On big pours, check the laser hasn't been knocked by re-reading your datum mark every so often — it takes ten seconds and can save the whole floor.

Step 5: Final Check

Once the surface is closed, run over the floor again on the same grid you surveyed at the start and compare readings. Most floor specs in the UK work to Surface Regularity classes (SR1–SR3), measured with a straightedge, but a laser survey on a grid will quickly show you whether you're in the right territory before anyone gets the 2m straightedge out.

Common Mistakes to Avoid

• Setting up on the area being poured. The tripod must be on ground that isn't moving or being worked.
• Not checking the laser's accuracy first. A laser that's out of calibration will put the whole floor out. Check it before you start — and if it's drifted, our Service 72 calibration will have it back to spec within 72 hours.
• Working without a receiver outdoors or in bright light. You won't see the beam reliably; the detector will.
• Losing your datum. Mark it somewhere protected and re-check it during the pour.

Which Laser for the Job?

For rooms and small extensions, the Grettz G60 rotary laser kit covers everything in this guide with a receiver and staff-ready setup. If your work includes drainage falls or sloping slabs, a dual-grade machine like the G80 green-beam dual-slope rotary lets you dial the fall straight in. Browse the full range of rotary lasers to find the right kit for your floors — every Grettz laser comes with UK support and a 3-year warranty.