Concrete shrinkage - how much and when does it stop

[Sean]

Can anyone give me any guidance here

I'm planning to shutter a hearth for a fireplace I'm building. As I want the hearth height to be as exact as possible, I'm a bit concerned about concrete shrinkage. Can I assume that for a reasonable strong mix reinforced that this is negligible? I dont want the seals on the stove flue leaking as a result of the hearth dropping

TIA Sean

[bigcat]

Concrete never strops shrinking. After about 70 years theres nothing left.

NT

[The Natural Philosopher]

Not so much the strength as the wetness. Mix it strong and as dry as you dare.