Sanded Grout Video
When the joints are too large for regular grout, sanded grout works because it will not shrink like regular grout. Sanded grout is mixed from a powder and water. Don't add too much water. The mixture should have the consistency thick enough so that is does not stands up and does not fold in the bucket.
The only tools needed to work with sanded grout is a rubber float (made of a hard rubber with flexible edges and very smooth) and a grouting sponge. The grouting sponge has rounded edges. Square edged sponges will not work.
Apply some grout on the wall with a spreading knife. The grout should not fall down if the consistency is right. Take the rubber float and get it wet to lubricate the edges. Use the float to drive the grout into the spaces between the glass blocks.
Next take the sponge and wring all the water out of it. Wipe light across the blocks. The sponge will smooth out the grout joints. Rinse the sponge often to remove the excess grout. To finish, rinse the grout sponge and wipe down the glass blocks very lightly. This should remove all or most of the grout on the glass.
Once the grout is completely dried, it can be buffed with a dry cotton rag or towel. It will look gorgeous.