Does Sawdust Do the Same Job as Bulking Agent?

4 April 2017  |  HOTBIN Composting

Does Sawdust do the Same Job as Bulking Agent?

No, unfortunately not. Sawdust is too fine and wood shavings are not thick enough to be a substitute for bulking agent. 

Bulking Agent Creates Air Voids in the HOTBIN
What is Bulking Agent?

Bulking agent is simply wood chippings; in our case we provide partially composted wood chippings which will break down faster than those that aren’t partially composted.

What Does Bulking Agent Do?

The job of bulking agent is to create air pockets within the waste as it is added to the HOTBIN.  These pockets allow air to circulate through the HOTBIN feeding bacteria with oxygen and keeping them composting aerobically. Without these air voids and access to oxygen, bacteria will start composting anaerobically which means a colder bin and often bad odours.

If you decided to use wood shavings or sawdust these would likely block aeration in the bin because the particles are so fine. The results of using both wood chip and sawdust in the HOTBIN is also discussed alongside why the carbon to nitrogen ratio isn't as important in the HOTBIN as it would be in other composting options.

I Don’t Want to Add Bulking Agent

Adding bulking agent is the trade-off for not having to turn and tumble a compost heap.

One of the most common causes for a HOTBIN not getting up to temperature is a lack of bulking agent (air voids) and/or shredded paper. Insufficient bulking agent prevents the contents from being sufficiently aerated whilst a lack of shredded paper can result in the contents becoming overly wet.

If you do not add bulking agent or a suitable alternative the HOTBIN is unlikely to operate as a hot composter. It is important for a bulking agent to have a certain particle size; sawdust for example is so fine it will just simply fill those voids blocking aeration.

Can Sawdust Replace the Job of Paper Instead?

Although sawdust does have some water retention properties, unfortunately they are not sufficient to control the moisture levels in the HOTBIN which is why we recommend shredded paper. The fine nature of sawdust also means that when it becomes wet it has the ability to clump together forming a damp impermeable mass in the HOTBIN.

Struggling to locate enough shredded office paper, here are a couple of alternatives.

Does that Mean I Can’t Add Pet Bedding?

Pet bedding (wood shavings and sawdust) can be added into the HOTBIN but only when it’s hot (40-60°c) and in small quantities mixed with other waste. The key here is to remember not to restrict airflow so don't forget to mix in paper and bulking agent too.