I'm making some exposed aggregate concrete blocks to match and repair a 70 year old garden wall.
I'm not doing too badly getting there by trial and error.
-Using a 1-2-5 mix with a small amount of plasticiser seems best, but is grainy and doesn't flow, so it's not great to work with, and voids result if I'm not careful. Any suggestions on a better mix? Is it better relatively dry or should I keep it wetter to make it more workable and flowing?
I use a stiff brush after about 10 hours to brush the outside of the blocks , and then hose down to expose the aggregate finish. Does that technique and time seem about right, or is there a better way?
They arent very strong when I take them out of the formwork, but hopefully they'll acquire more strenght over a few days, or would a different mix be stronger?
I'm going to try adding a bit of soil (!) to the mix in the hope that they'll look a bit older. Might this work?
That tapping technique works really well. Y' can see the level in the mould drop slightly and occasionally the bubbles of air escaping.
I have another question - the variable unpredictable quality of my concrete.
Sometimes the blocks I make turn out good and strong, but my latest batch are pretty chalky, and I don't know why. After 24 hours of a 1:2:4 mix, they're still soft. I appreciate it takes days for concrete to cure properly, but I thought they ought to be stronger than that. I've started adding a bit more water so that it flows more easily into the mould- perhaps that's the problem -would it weaken the product? Or is it just the cooler weather slowing the process down? Perhaps if I add pva it might help?
THe blocks have a 1cm square lip at the front which overhangs the block below - this is the bit that needs to be strong, else it'll snap off.
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