Here's the page on our Mosaic fixes. This goes along with out dragon mosaic tutorial.

When your finished with your mosaic several problems may occur after placing the grout. Sometimes the grout does not completely mix and you are left with white spots. We fix this simply by painting the problem areas.

Another issue that may come up is the loss of tiles. Sometimes the grout does not completely seal in all the tiles if they are of varying height. In order to fix this simply take a pencil or something similar and place a little grout where the tile was lost and replace it.

Also sometimes the grout does not evenly mix and you get air bubbles that pop up in the grout leaving small holes. To fix this simply add in a little grout like you did with your replacement tile.