Vivaro, I'm wondering to myself do you really need one? I have not seen a 3mm notched margin trowel. In my (limited) experience it is easier to butter the adhesive on the back of the mosaic with your normal sized 3mm trowel. I have a 6mm notched margin trowel, but I hardly use it, as it is sometimes too big to fit in tight corners or in between electric sockets. Cheers Sean
dave just get a piece of thin plastic and cuts notches into it ...these can be cut to any size you need.......bit like the diy adhesive combs you get in the tubs of the all in one stuff......
Those margin trowels are more for back buttering not really for getting into hard to get at areas..but they would work.........