If you make each piece a component, you will be able to keep the materials separate. Is that a piece of 2x material? with mortar underneath? before you bring the mortar up triple click the 2x material and make it a component. then when you bring the mortar up it will not take on the material of the wood. By making everything in your model a component it will be easier to edit discrete pieces of your model. Hope this answers your question.
Brooks