All recommendations are welcome. In particular how to vibrate a two part mold without it breaking apart. I did not weigh the mix and water, but i suspect i used too much water. Also added about 2% plasticizer.
this post was submitted on 03 Aug 2025
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Haven't vibrated it enough. 100%. But it's interesting because your void distribution is pretty consistent... im guessing you vibrated the mould rather than the mix.
Your problem is not mix consistency, it's entrained air. Mould vibration (esp with a small mould) is not good at removing entrained air.
Try a needle vibrator on your next one. Maybe an old tooth brush?
Edit: don't forget to treat your forms. You want to apply specialised compound to reduce adhesion between concrete and form, so when you strip forms, pockets of uncured mix don't 'pull away' from your piece.
Thank you for the advice. Do you really think a toothbrush will work? ^^ I read somewhere that oil spray (you know for pans and stuff) was good, so i tried that and it seemed to work fine, the form slipped pretty easily.
Pam or similar should be fine as a mould release. A YouTuber we watch, Evan and Katelyn, did an experiment testing different vibration methods for concrete, and they found a personal vibrator (yes, that) was the best for smaller projects like this.
https://m.youtube.com/watch?v=OOFOxDiOgEA&pp=ygUZRXZhbiBhbmQgS2F0ZWx5biBjb25jcmV0ZQ%3D%3D
Both good options. Don't need to be fancy, so long as it works.
Re the vibrator recommendation - that's hilarious but apt. You want something that doesn't move a lot, but oscillates a ton. A vibrator fits those requirements. A mechanical toothbrush could work in a pinch, but you don't want the rotating toothbrush head, it's the motor vibrations (offset? Can't remember) doing the trick.