How do I level uneven concrete, asphalt or tiles?

Installation instructions for laying tiles in a straight grid pattern require uneven concrete, asphalt or tiled surfaces to be levelled using a material suited to both the existing substrate and the depth of the irregularity.

For shallow irregularities in concrete, an adhesive filler or repair mortar can be used. Larger defects in concrete are filled with repair concrete. Asphalt surfaces are repaired with a suitable asphalt repair compound. On tiled surfaces, use a levelling compound appropriate to the intended application. Loose or damaged tiles must be fixed or replaced beforehand.

Before laying loose-laid rubber granule tiles, small depressions where water collects can be levelled with accurately cut pieces of roofing felt. Several layers of roofing felt may be placed one on top of another if required. Check the result with a long straightedge or a straight metal bar.

Roofing felt is suitable only for localised irregularities and does not replace any necessary substrate repair. Sand, gravel and chippings are unsuitable for levelling on bound surfaces: the loose particles cannot be compacted permanently and may move under load or due to water, creating further unevenness and leaving the tiles laid above unstable.