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Mixing and pouring the concrete

A project log for Onix - Yet another concrete Lathe

An upgradable, scalable 200$ Lathe for everyone* (*with some basic tools)

moritz-wenzelMoritz Wenzel 10/22/2018 at 20:370 Comments

To get the block easier out of the mold later you can apply a thin coat of vegetable oil or seperating wax on the inside of the mold and the place holder pipes, but be careful not to apply anything on the threaded spacers or the rebar since these parts are supposed to stick to the concrete. 

For the concrete i used a mix (screed concrete) from the hardware store which is not too coarse and worked well for other projects in the past. I also mixed in some glas fibres (AR-Glas, 12mm) i used 20 grams for each 10kg concrete mix, this might sound like nothing but already improves the properties of the concrete and prevents fine cracks during the curing process. 

Besides that i also mixed in some pigments, so it would look cooler, that is totally not necessary but if you want to be creative there are pigments in many cool colors, so if you have a huge block of concrete in your shop, why not making it at least look good. 
I used a 2% ratio of the pigments. so 200g for each 10kg concrete mix.

You will need 37,5kg of concrete mix (I bought 2 bags each 25kg and ended up using exactly one and a half, so just for you as orientation. 

Edit: Please read my advice about the viscosity of the concrete and the recommendation to use special "Concrete Liquifier" here before continuing since i ended up having some holes and gaps in the bottom section of the block. 

I used the amount of water they claimed on the bag with was 2,5 liters of water for 25kg concrete mix. That results in a nice viscosity/consistency maybe a few drops more would be fine too, but you don't want to end up with a soup, that will just weaken your concrete. If you compress the mixture every ~5cm while filling your mold, you will end up with a nice result better than filling the entire mold and then try to compress anything, you will probably end up with air holes and pockets. I added two pieces of rebar inside the concrete to improve tensile strenght.

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