My Darrier paste is grainy. Zinc oxide 25g Ca carbonate 25g glycerin 25g Aqua Dist 25g

The graininess is not normal. First of all I would suggest you use calcium carbonate light. The graininess I think comes from the ZnO. The glycerin must be properly used to acquire it beforehand. You can optionally add 0.1% Tween 80 to improve humidification. Afterwards, you gradually mix calcium carbonate with the previous mixture under harsh rubbing. To eventually dilute with water. If the whole is too liquid then 1% Aerosil can be added. If a free viscous paste is obtained, the whole can be treated with the ointment grinder or with a zalfmengmachine like e.g. the Unguator or Topitec.