The grout is unevenly finished in colour and may have a dirty appearance [Photo 1].
Technical reasons for patches in the grout
Morgan advises that there are numerous causes for patchy areas of light and dark within a grout –
- Tile spacing lugs were left in the grout joints
- There are inconsistent grout joint depths and gap widths
- The tile adhesive has not been cleaned out of the tile joint before grouting
- The tile or natural stone varies in density and porosity
- Variable glaze on the tile edges caused the grout to cure at different rates and led to shading
- The concrete substrate was not fully cured or had a high moisture content
- Direct sunlight or too large an area grouted at one time before clean-up is initiated
- Grout joints were excessively wiped during the initial cleaning process.
Recommended procedure for repairing patchy grout
Grout that has cured with a patchy appearance needs to be removed completely to the substrate and re-grouted.