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.
Consider lubricating the inside of the mould so it’ll release better and some reinforcing mesh. eg, cooking oil spray, raw fiber glass.
Out of curiosity, what are you making?
I want to make a drain where this puddle forms, but stock drains from hardwarestores expects more difference in the ground levels. I only have a few centimeters to work with to a french drain around the corner, so i want the outlet to be on the side close to the surface. I have a drain grate that will fit on top of this thing.
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.
The vibration required is pretty serious. If you look into how they make concrete bricks you need a lot of force and control for the frequency to make it effective.
I used this as a basis designing a table to vibrate epoxy-concrete molds for machine tools. You’d want the dildo attached to a hammer drill style vibrator for small scale application. https://i.imgur.com/RcIcqk1.jpeg I used a steel plate here, 2hp Craigslist motor, bicycle tubes, rubber and wood. My plan was for larger molds…
That, and the aggregate ratio also being the two critical parameters. Edit: the whole requirement is also dependent on your needs. You can change a lot if you don’t need serious strength to better target surface finish.
I forgot i had this, will try it though the frequency is probably lower than what you suggest.
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That many voids implies not enough vibration to me
how do you vibrate? do you try to vibrate your whole mold? like using a “concrete vibrating table”?
maybe you can build you a equivalent of a “handheld concrete vibrator” in even smaller, and just put it into the concrete?
Well i just tried holding the bottom of my multicutter onto the mold, probably was not enough. Maybe if i put the entire thing on a plate i can vibrate the whole plate somehow…
I’m no expert but maybe also need some more larger particles in the mix. Is this just cement and sharp sand?
