Constructional Vs Construction?

Can anybody explain to me why it is not right to say constructional materials? I don't understand why construction (a noun) is more appropriate than constructional (an adjective) Thanks ^_^

Constructional materials sounds rather ugly to my BrE ears. The first word is made up of four Latin elements and it is followed by a Latin (via Old French) word. It's just too much Latin! Construction materials is perfectly clear. Governmental is similarly abbreviated to government where its adjectival form might seem more correct grammatically.

Also, both constructional and material(s) end with -al. And each is made up of two iambs, which means they are stressed identically. So although they don't rhyme exactly, they certainly jangle when they're put together.

BUT there's nothing actually wrong with constructional materials and I'm not sure why you say there is. If some grammar-checker disallowed it then it must be because the word constructional is not much used nowadays.

Ngram shows the relative use of your two expressions and the decline of constructional. In the UK the word seems to have peaked at the end of WWII. Perhaps military leaders use Latinate words more than the rest of us.