How large can a gap in the mold be with coarse concrete without it flowing out?

[Martin Lj]

I will cast about 40 cavities in my crawl space, which lock together the blocks the foundation is built of, as shown in the picture below.



However, there are quite a few gaps because the blocks aren't completely perfect. How large can the gaps be without the concrete running out, so to speak? There are gaps up to ~3mm.



I was considering sealing the gaps with some outdoor sealant, or is that a bad idea?

 

[useless]

It sounds like a silly idea. Gaps of a few mm are not a problem.