What is the best mix to make chalk paint at home?
You will need a good binder, and the cheapest waterproof binder that you can make yourself is casein.

Casein is a milk-based product that you can make by warming  whole milk in a saucepan and adding about 5 drops of lemon juice per liter. You don’t have to get it hot, but it mustn’t be cold. You will see clumps forming, and then remove it from the heat. Pour the entirety through a fine-meshed strainer and reserve the watery part (the whey). I like to let the casein dry for about 24hrs. Do not leave it in the sun, and do not accelerate the drying in the oven.

The next phase is to do what the Germans call “sumpfen”, and that means you soak the chalk for 24 hours in a clean bucket with distilled water before you mix it into the casein. While it is soaking, you can stir it several times to make sure that it is mixed thoroughly. It will settle to the bottom of the bucket. Don’t use too much water, because it isn’t necessary. Just use enough to cover the chalk.

The next day when it is time to paint and your surface is prepared (i.e. no grease spots, sanded down etc.) take one part casein to one part chalk and knead them together like bread. Once the consistency is uniform, put the casein-chalk in a paint pot and slowly add distilled water (even from the chalk bucket) until you get the consistency you want.

It is really a good idea to try out your technique and the paint on a piece of wood similar to the table. When the paint is dry, you can burnish it with a silk pillow, for example.

If you have extra casein, wrap it in plastic and keep it in a dark and cool place, like the fridge.