walls that use large stones put together without any attempt at courses is called rubble walling. they are laid at random and are held together with mortar. where similar work is laid in courses, it is known as coursed rubble. dry-stone walling is somewhat similar work done without the use of mortar. it is bound together by the fit of the stones and the regular placement of stones which extend through the thickness of the wall. a rubble wall built with mortar will be stronger if assembled in this way. building foundations made of rubble almost always leak water and are damp.