An important concept is life is to recognize resources and know what uses they can be put to.
There is not waste resource, just a wasted resource opportunity.
So what is in wood ash?
Wood ash makes up 0.34 to 1.8 percent of the weight of dry wood burnt in its production.
So 10kg of wood burnt will produce at least 34 grams of dry wood ash.
Wood ash is a good thermal insulator if it is kept dry, the small air pockets in it allow for it to have this insulating property, once it becomes damp or wet these air spaces collapse and do not return upon drying.
Wood ash is:
about 25-45 % Calcium Carbonate ( CaCO3)
About 10 % potash (K2CO3, KCl , K2SO4)
about 1% Phosphates (PO4¯³)
The temperature and duration of the fire will influence the composition of the wood ash.
For example ta higher temperature will reduce the Calcium carbonate to Calcium oxide and make any resultant Lye more alkaline.
Wood ash is also used in odor control in composting especially if it has a high char content.
By adding water to Wood ash, Lye is produced, an alkaline mixture of Calcium and potassium hydroxides, thought the calcium salts will precipitate as it is not very soluble in alkaline solutions.
Lye is commonly use to reduce acidity in soils
Lye is also used in making Soap
Lye can also be use to clean clothes directly by in doing so you are relying on the oil in the clothes being turned to soap during the washing process.
So it will be a lot slower and you will have to heat your water.