Large Mosaic Mural - Problem

[Tilerman]

Hi Guys
Just working on the design for a large black and white cut mosaic mural, 140cm x 200cm, but I have come accross a slight problem! Most of the design is fine and is made up of large cuts, but part of the design is black lines through white, that are 3 - 4mm thick, don't think it's possible to use tile cuts for this, so I was thinking about using grout lines to define these lines, only problem is I would have to use two different grout colours in the mosaic! black to define the line and white for the background, has anyone ever heard of someone doing this? I know it would be messy but I don't see any other way of doing it, if I used tiles they would basically be held by the grout. I attached a 20cm x 20cm grid section of the mosaic so you can get an idea of what it's like.
Cheers lads

I can't make sense of the picture to be honest mate.

But it sounds like a good idea to me mate.

[Tilerman]

Sorry about the picture! I only uploaded a small grid section to show the lines, uploaded the full picture this time.