How much bulking agent is required?

Friday, 6 January 2012  |  HOTBIN Composting

Bulking Agent Ratios

Bulking agent is required to create an areation chimney.

When composting mainly food waste its reccomended to add 1 part bulking agent to 5 parts food waste. The top 10cm layer of food waste in the HOTBIN should have 4 litres (two measuring jugs or 6 hands full) of bulking agent in. A bin ¾ full of just food waste should have a total of 16 litres (just short of a full carrier bag) of bulking agent added to it over the filling weeks.

This table gives you a rough idea of what that translates to:

  Full food waste container (by volume in litres)
Container Kitchen measuring jug Small plastic kitchen waste caddy Medium kitchen waste caddy Full carrier bag, plastic bucket or large food caddy
  2 litres 5 litres 9 litres 18 litres
Add this many hands full of bulking agent per container 0.5 1-2 3 6
Ratio by volume For every full container of food waste, add one fifth of bulking agent (The volume ratio is 1:5)

Note: The amount of bulking agent that needs adding will depend on the waste mix going into the bin. If other woody waste is being added from the garden, then less bulking agent will be required, a 1:10 ration rather than 1:5.

Do I need to add bulking agent if using paper?

Yes, ALWAYS add bulking agent with food waste. The bulking agent will form a supportive structure that maintains airflow.

Remember: In hot composting, paper fixes wetness and wood chip helps aeration. You cannot balance ‘wet waste’ by adding wood chip bulking agent, nor can you fix ‘poor aeration’ by adding paper.