I got this basic shampoo recipe off the net:

4 ounces Pure white castile soap
1 quart spring or distilled water

Finely grate the the soap. Bring the water to a simmer and add the
soap. Bring this to a boil until the soap has all dissolved. Pour
into a jar and store until needed. To this base add various oils,
herbal infusions and Essential Oils to create the shampoo best suited
to your needs. Follow with conditioner and rinse well.

I am wanting to make some today, but it seems like it would be pretty
thinned out. Does the soap thicken up after it cools or would I need
to add anything else to it, and if so what.