Knossos

In order to tile over existing glass mosaic tiles it is essential to treat them first with something that will allow the tile adhesive to stick to the smooth surface. This is a sticky varnish with gritty sand that comes ready-mixed in a bucket for rollering straight onto the existing tiles. We hadn't expected it to be Knossos red but I suppose that would contrast against almost any existing finish and therefore help you to see if you had missed a bit.