And cause brick spallingRender on solid walls must be lime render. Render on cavity walls contain cement.
Solid walls breathe through the mortar joints. Repointed with cement mortar and/or rendering with cement render stops the wall breathing, hence why they become very damp inside.
What does " your 1930's walls could very well contain as many bricks as stones" mean? Stones in a typical 1930's house?
What does mention of "timber ... lintels" have to do with the OP's question?
"how a property is treated inside" means what? "simplistic" how?
To say lime or cement render is a myth is pretty wrong.
Portland cement powder and NH Lime powder are miles apart in many ways - they affect render and mortar in different and distinctive ways
Technically, even scrap iron is an ingredient in cement but it has virtually nothing to do with renders or mortars on site.