Cracks, lifting tiles, or uneven floors can be worrying for any homeowner. Our latest Specific Defect Survey highlights a fascinating yet serious cause — sulphate attack in a concrete floor slab.
Case study
A 1950s semi-detached property began showing cracking and lifting of kitchen floor tiles. The kitchen floor, once level following a 2020 renovation, had since developed a visible slope and a high spot at one corner. Further investigation revealed tiles lifted and lipped with open joints around their edges, along with crystalline deposits beneath the tiles and surface disruption in the slab itself.
Diagnosis: localised sulphate attack
Sulphate attack happens when sulphates present in some hardcore or fill materials react with the concrete above, causing it to expand. That expansion is exactly what was lifting and cracking the tiles — not settlement, and not the more commonly assumed damp problem.
Recommended actions
Once the cause was confirmed, the recommended repair was targeted at the affected area rather than the whole floor: removing and replacing the affected slab section with a suitable damp-proof membrane and sulphate-resisting specification, rather than a blanket re-screed of the whole kitchen.
The takeaway
An uneven or lifting floor can have several very different causes, and the right repair depends entirely on getting the diagnosis right. Treating the symptom without understanding the cause risks the same problem recurring.
Noticed lifting tiles or an uneven floor? Get in touch and we will help you get to the bottom of it.