I have rectified tiles throughout my house - on a lot of the grout lines, the tiler seems to have not used enough grout - and the grout is a couple millimeters lower than the tile. This means the rectified edges chip easily, dust gets in them and they just look wrong. Can I just add more grout to the grout lines that need it? I am worried that it will not adhere. Alternatively, there is a Selleys silcone product (in the long tubes that you squeeze out with a gun) that is the correct colour - would it be better to apply this, instead of grout?
Welcome to the Bunnings Workshop community @Corin. Many thanks for your question, I'd be happy to give some advice.
It's great to have you join us and we look forward to assisting with your project. I've spoken to one of our grout manufacturers and if the rectified tiles are either ceramic or porcelain then I would recommend Davcos rejuvenation grout. Existing grout must be at least 1mm below the surface of the tile, allowing sufficient depth for the rejuvenation grout to bond to the grout joint. The tile and grout surface must be thoroughly cleaned with either a mild soap and water mixture or sugar soap mixture. If required, a bristle brush can be used to clean the existing grout joints. Following the cleaning rinse the surface with clean water.
This grout is specifically designed with a high bond strength for use in applications likes yours where you are filling on top of existing grout. Personally, I would steer clear of silicones as they might cause issues after some time.
Please let me know if you would like further assistance or had questions.