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Bulking Material For Composting Toilets

Peat moss has long been the recommended bulking material for compost toilet users. Over the last few years, we have discovered that peat moss on its own does not make a good bulking material. Peat moss packagers have been pulverizing it for gardening applications for the past few years, making it very fine, and coarse peat moss is very hard to find. 

Since it is now fine and powdery, it does not allow the compost to be as aerobic as we would like. Fine peat moss will compact and leave very little in the way of porosity in the compost, which slows composting dramatically.

However, peat moss is still required in self-contained units to cover fresh urine odors and absorb moisture, so we cannot dismiss it entirely. We have experimented with a number of different materials to mix with the peat moss, and have finally decided on two as excellent additives. 

The best material we have found so far to mix with the peat moss is dried hemp stalk, chopped into 1" pieces. This is available and pre-mixed from Sun-Mar and is called Compost Sure.

The Compost Sure mixture consists of coarse peat moss and dried hemp stalk. 

The hemp stalk pieces are sharp, and cut into any lumps that may form in the compost, breaking them up for faster composting. In addition, the hemp stalk is the only bulking material that we have found that actively breaks down in the compost while still adding carbon to the compost. 

Since there is less material in the composter, the compost residency time is longer, which contributes to a better quality of finished compost. Because of this advantage, we recommend that all compost toilet owners use this when possible or pre-mix their own. 

Where it is not possible to use Compost Sure bulking material, the ideal homemade bulking material for all composters should incorporate wood shavings.

"Wood Shavings" is a broad term, so we shall define it further here. Any wood may be used except cedar, and the ideal shaving is a light and curly shaving such as the kind that you would get from planing a board. 

These are generally available through your local sawmill, or a friend's workshop. The shavings should be over 1" square in size as smaller shavings tend to pack and slow the composting process. 

If you are making your own bulking material, the ideal ratio of mixture for a self-contained unit or central air flow composting system is 60% wood shavings and 40% peat moss. 

The ideal ratio of mixture for a central flushing system is 75% - 100% wood shavings and 25% - 0% peat moss. The reason that you can get away with 0% peat moss in these systems is that the urine is diluted by the flushing liquid, so it is not as necessary to cover urine odors in these models. There is also an abundance of liquid, making the moisture retention qualities of the peat moss unnecessary. 

If you are still using peat moss on its own, switch now! You will notice a vast improvement in your composting action in a very short period of time. 

If you have been using peat moss alone for quite some time, use 100% wood shavings as your bulking material for a couple of weeks or until the mixture in your drum looks like it is about 60% wood shavings and 40% peat moss - then switch to the homemade mixture mentioned above or Sun-Mar Compost Sure.

Off Grid And Green
Off Grid And Green


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