Real building material (8)
I believe the answer is:
concrete
I believe this clue is a double definition.
'real' is the first definition.
(similar in meaning)
'building material' is the second definition.
(concrete is a kind of building material)
(Other definitions for concrete that I've seen before include "Specific; definite" , "Unsightly building material" , "setter" , "It's composed of sand, cement and water" , "Building material is not abstract" .)