An uneven garage floor creates practical problems for vehicles, tool storage, floor-standing equipment, and door seals. The appropriate levelling method depends on the extent and nature of the unevenness.

Assess the Unevenness First

Lay a long straight edge or a spirit level on the floor in multiple directions and note where gaps exist beneath it. A gap of up to 5mm across a 2-metre straight edge is relatively minor. Gaps of 10mm or more, or a significant slope across the floor, require more substantial treatment. Note whether the unevenness is concentrated in specific areas (typically caused by subsidence, cracking, or wear) or spread across the whole floor (typically a drainage slope or original laying imprecision).

Self-Levelling Compound

For unevenness of up to 10mm to 15mm over a reasonable area, a self-levelling floor compound provides a practical solution. The compound is a powder that is mixed with water to produce a flowable consistency, poured onto the floor, and spreads itself level under gravity. It is suitable for filling low spots and for creating a level surface over a moderately uneven floor. The floor must be primed with a floor primer before application to ensure the compound bonds correctly and does not pull away as it dries.

Concrete Repair Mortar

For isolated raised areas, damaged sections, or specific low points rather than general unevenness, a concrete repair mortar or floor patch product is more appropriate than self-levelling compound. Apply the mortar to the problem area, build it up in layers if needed, and finish flush with the surrounding floor using a float. Allow to cure fully before use.

Full Screed Overlay

Where the floor has a significant slope, multiple areas of subsidence, or general unevenness that cannot be economically addressed with self-levelling compound, a full screed overlay provides the most comprehensive solution. A sand-cement screed of 50mm minimum thickness is laid over the existing slab, screeded level, and allowed to cure. This raises the floor level significantly and must be planned around door thresholds and internal access steps.

Summary

Level minor unevenness up to 15mm with self-levelling compound over a primed floor. Address isolated damage or low spots with concrete repair mortar. Correct significant slope or general unevenness with a full screed overlay of at least 50mm. Preserve any existing drainage slope toward a floor drain. Assess the extent of unevenness before choosing a method.