The joint, when properly applied and treated, should not allow discolouration. Discolouration may result from the following:
- excess of adhesive has not been removed from gaps between tiles,
- water, especially while jointing porcelain tiles, was overdosed
- insufficient cleaning and dedusting of the tile and joint surface,
- tile edges have not been moistened with a sponge,
- dirty tools and containers were used,
- excessive drying of joint mortar due to high temperature, draught or highly absorbing surface,
- joint grout from different batches was used,
- too long intervals took place while pointing.