If you tap on the cinder or concrete blocks with a hammer, and this is also true with granite, you will hear it ring. Not really good materials for a turntable base. I know because I also tried it once myself years ago. Better materials to use will "thunk" when you tap on them. Sand filled or small ball bearing filled wood boxes are a good way to add mass to a base.
Lastly, spring isolation of the base, provided the turntable is unsprung is very effective.