You are stepping into a bit of a complicated area. There are (at least) two ways of dealing with this. You could dive into UV mapping to make sure your shader is not mapped over the whole object, but just per wall or something (I am thinking bricks).

Another solution, is to get one of the most important plug-ins made for Carrara: Shader Ops from DigitalCarversGuild. It has Programmable Scale, Size and UV Repeater components that will help you scaling your shaders.

Hope this helps!