u/Raukey

Hello everyone. I hope you're all good
I have a concrete casting problem i never faced before on a tiny relief casting (35x26x2cm). I'm usually making concrete casting but the 2 last time i did it I had some little dry and crumbly zone (1cm²). Maybe it's because of some tiny chunk of concrete not mixing with the rest. My recipe is only concrete and water, with some wire mesh. i normally do this recipe without problem but the 2 last i had this issue.
My mold is a mix of silicone and 3D printed PLA (i already used those material to).
I put a picture of the casting. Do you already got this problem or do you know how to fix this ?