So far im using a blend where castor oil makes up at least 1/3-1/2 of the bottle. I mixed certain essential oils, grapeseed oil, and argan oil. When im using straight castor oil I noticed that a lot goes a long way however it makes my hair feel great. I do a hair mask with it on wash day and apply a really small amount of it on specifically on my ends before brushing my hair out.

In the few days when I first started using it, my hair has felt so much better. Didnt notice build up.

I will say that it's better if you mix it with other carrier oils like jojoba, argan, almond, avocado, rapeseed, apricot, rosehip, coconut, sunflower or olive to make application easier. Gentle heat will also help with making it more fluid and add a few extra benefits. If you're going for essential oils, castor oil is a good carrier oil to dilute them with (as you always should).

As for helping people's hair grow, it has yet to be determined by dermitologists that castor oil by itself helps hair growth, but it certainly helps with moisture.