concrete block making advice

I'd been looking at a spot behind an old tennis court that needs a bit of retaining and levelling to stop run-off from the court surface and wondering what to use for the job when I was given a concrete block mould. I have been making a few trial blocks and wonder if there is anyone with prior experience that could give me a few tips. So far I've used a 4:1 concrete mix without much aggregate (fines are off the side of our dirt road) and find that I need to let the mix set in the mould for...

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