6 Best Cover Materials for Composting Toilets [And 3 To Avoid]

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Is there anything worse than a smelly composting toilet? I don’t think so.

Thankfully, cover materials solve that problem.

The best cover material for composting toilets needs to be:

  1. absorbent enough to help control moisture levels
  2. porous enough to allow oxygen into the mixture
  3. good at controlling odours

If you want to skip the (potentially very gross) trial and error phase of finding the best composting material for your toilet, then read on for what ( think are the best (and worst) options.

Best Overall

Coco Coir

Coco coir is great at preventing odors, easy to store, and environmentally friendly.

Also Great

Hemp Stalks

Hemp stalks are super absorbent and great at masking smells. They also break down in compost quickly.

Don’t Forget

Diatomaceous Earth

Diatomaceous Earth is best used alongside another cover material and works wonders at controlling pests.

My Pick For The Best Covering Material For Composting Toilets

My personal favorite composting toilet cover material is coco coir.

It’s very good at preventing odors, and it’s easy to get a consistent supply.

However, the biggest plus for me is the ease of storage. It comes in compressed blocks that can be stored anywhere, making it perfect for anyone with limited space (such as in an RV).

I mix the coco coir with some diatomaceous earth to prevent any bug infestations. I explain more about why diatomaceous earth is so useful later in the article.

If you want something specially formulated for composting toilets, then this peat and hemp mix from Sun-Mar is a good option.

Best Cover Materials For Composting Toilets

I picked these materials because they all do an excellent job at preventing odors and controlling moisture.

But each of them also has other unique advantages and disadvantages to consider.

Coco Coir

Coconut Coir is a natural by-product of the coconut growing industry. It’s made from coconut husks that might otherwise go to waste.

The covering material is widely considered to be an eco-friendly, sustainable alternative to peat moss.

However, there are some environmental concerns. Because most coconuts are grown in Asia coco coir has a relatively high carbon footprint compared to other resources produced in the USA.

It usually comes packaged in highly compressed blocks, which you’ll need to soak in water before use. After soaking, the blocks will expand to around three times their original size, so make sure you use a big enough container!

This makes coco coir a great choice for anyone with limited space because you can store a large quantity of composting material without taking up much room.

Before purchasing coir, take a look at how it was produced. Some producers soak the husks in saltwater. And high salt levels are not good for compost. Others chemically treat their coco coir.

Coco bliss rinses their untreated organic coco coir in freshwater to ensure a low EC/salt level.

They also use smaller blocks than most sellers. This makes it easier to prepare the coir for use.

When I purchased one big block, I found it very hard to break the material up into smaller bits to soak. The smaller bricks are a lot more convenient.

Pros
  • renewable
  • highly compressed for easy storage
Cons
  • high carbon foot print
  • need to prepare for usage

Hemp Stalks

Hemp is a plant that’s grown for use in various applications, including food and textiles. The stalks from this plant make a fantastic cover material – it’s super absorbent and great at masking smells.

One advantage of using hemp is that it’s quick to break down in compost, unlike other carbon-based covering materials that can take a while.

Another significant advantage for hemp is that it’s one of the most renewable plants around and, therefore, a very eco-friendly cover material for your composting toilet.

It grows quickly, doesn’t require any added fertilizers or pesticides, and uses very little water.

Furthermore, it can be grown in a variety of climates. It’s produced all around the world, including the USA.  If you can find US grown hemp, this helps to keep its carbon footprint minimal.

Unfortunately, it can be quite hard to find locally. You can try a local equine shop if you live near one as it’s a common material used for horse bedding. If you do manage to source some, make sure it’s chopped into small pieces before use.

But if you can’t, then you can get hemp animal bedding online. While the product is advertised as pet bedding, it will work well in a composting toilet too.

This hemp bedding from American Hemp is grown in the USA and is less dusty than some of the other options.

Alternatively, you can try this peat and hemp mix from Sun Mar. This mixture is specifically designed to work in a composting toilet.

Pros
  • sustainable
  • breaks down quickly in compost
Cons
  • can be hard to find
  • may need chopping up before use

Peat Moss

Peat moss, otherwise known as sphagnum moss, is another commonly used material in composting toilets. It’s made from the decomposed remains of living organisms found in bogs.

It’s very absorbent, so good at removing excess moisture. And it’s also very good at odor control.

However, some people have noted that peat moss manufacturers have been making their moss finer over the year. This is useful for garden applications, but not so great for a cover material.

This means it can be messy to work with, and it quickly loses its porous nature, which can block air from reaching the mixture.

To get round this, you can add a bulking medium to your peat moss such as wood shavings or coco coir. The ideal ratio would be around 40% peat to 60% bulking material.

Furthermore, it’s lost popularity recently because of environmental controversy around the sustainability of peat moss.

Peat bogs only grow at a rate of around 1 mm a year. This means that after you harvest a peat bog, the damage can take hundreds of years to repair.

Despite all this, I’ve still included it in our best list because it’s very easy to get hold of and if used with a bulking material peat moss is one of the best cover materials for composting toilets. In fact, this is what Sun Mar uses in its cover material product – peat mixed with hemp as a bulking agent.

Just make sure your peat moss doesn’t contain any fertilizer. The best peat moss for composting toilets is either Premier peat moss, Hoffman peat moss, or Perfect Plants organic peat moss. They’re all high quality, fertilizer free products.

Pros
  • easy to get hold of
  • ready to use straight away
Cons
  • not the most sustainable
  • can be too fine

Wood Shavings / Sawdust

Wood shavings or coarse sawdust can make a very cheap and convenient composting toilet cover material.

You might be able to find these going free from a local mill or carpenter.

Alternatively, you can buy wood shavings in the form of animal bedding. This often comes somewhat compressed, so it can be easier to store.

Before you use the wood shavings, if you can, I recommend leaving them outside for a while. Somewhere under cover where they’ll get damp, but not soaking, is best.

This will activate the material and allow bacteria to build up, making it a more effective brown material.

If you’ve managed to source fresh wood shavings (not kiln dried), then don’t worry about leaving it as it’ll already be biologically active.

Most shavings are fine to use. However, I don’t recommend using cedarwood shavings. Cedar is naturally rot-resistant, and the shavings will take a long time to break down.

Very fine sawdust is also not a great option.

While it’s a good absorbent, it lacks odor control unless you use a lot of it, and it’s very dusty.

I haven’t tried fine sawdust in a composting toilet, but I did try it as a cat litter and quickly stopped because it was just too messy!

Some people suggested I tried wetting the sawdust slightly to give it a bit of weight, which could work for a composting toilet, but our cat didn’t like this.

Pros
  • cheap (can be free)
  • readily and locally available
Cons
  • slow to compost
  • needs prep before use (for best results)

Chopped Straw

Straw is an agricultural by-product of cereal plants such as barley and wheat.

These crops are produced in abundance, making chopped straw a sustainable and eco-friendly cover material.

You should be able to source straw from any local farmer. However, you may need to chop this straw up before using it.

Ideally, it should be chopped into pieces no longer than 3-4 inches. Any larger and it’ll become less efficient at preventing smells.

Chopping straw can be difficult and gives off a lot of dust.

If this sounds like a lot of effort, then you can buy ready chopped straw or straw meant for animal bedding.

Straw isn’t the most absorbent material on our list. In our experience, it works best when mixed with another more absorbent material like coco coir.

As with wood shavings, it can help the composting process if you leave the straw out for a bit before using it to start the bacterial build-up.

Pros
  • can be locally sourced
  • can be free
  • eco-friendly
Cons
  • may need chopping which can be difficult

Wood Chips

best cover material for composting toilets wood chips

Wood chips can be both good and bad, depending on the size of the chips.

If the chips are small enough, then they’re good at covering up odors and controlling the moisture levels.

However, if the chips are too large, then they’re less available to any bacteria and won’t be compact enough to keep smells from escaping.

If you find yourself with some too big chips, you can still use them, but I recommend mixing them with a finer medium like peat moss. Or you can use a good chipper shredder to reduce their size.

The best type of wood chips to use is semi-composted wood chips.

If you leave the wood chips lying around, they’ll naturally start to break down and compost.

They’ll work just like regular wood chips, but with the added benefit of composting faster at the end because microorganisms are already present.

To get hold of some for free, try asking a local tree surgeon if they have any to give away. Or try Chip Drop, a website that matches arborists with people who want free wood chips.

Pros
  • can be free
  • can be fast to compost
  • locally available
Cons
  • need to be the right size
  • needs to be left before use (for best results)

Diatomaceous Earth

Diatomaceous earth is a naturally occurring sedimentary rock. The rock is continually regenerating, making it a very sustainable material.

Gardeners routinely use the powder form of diatomaceous earth as a form of pest control, and it can also be used in a composting toilet to control gnats and flies.

Because the diatomaceous earth product is a powder, it’s not suitable for use as a cover material on its own. It would get too wet and slimy. But when you combine it with one of the other options I’ve recommended, you’ll have zero pest problems.

You can either sprinkle a little over the toilet after each use or mix it straight in with your other cover materials.

The powder works by sucking oils and fats out of a bugs exoskeleton, causing them to dry out and die. If the powder gets wet, it’s not as effective, so it works best in a separating toilet. 

Diatomaceous earth also has a lot of uses outside pest control. You can even use it in your skincare routine.

If you plan to use the product for multiple things, it’s best to get the food-grade product. But if you’re only going to use it in your composting toilet, then you can get away with the insecticide grade stuff.

Pros
  • prevents bugs
  • has multiple uses
  • eco-friendly, sustainable
Cons
  • not a cover material on its own

What To Avoid as a Composting Toilet Cover Material

While these can be suitable resources for traditional garden compost, they aren’t so great when used as a covering material for composting toilets.

Wood Ash

Ash is an absorbent resource and is well known for its odor suppressing properties.

However, it can be extremely messy and difficult to clean up. It’s also not very nice, or healthy, to breathe in ash.

Grass / Leaves

These can be okay when they’re dried and completely free of bugs, but it’s not practical for most people to store lots of dried grass, and it can be very time-consuming to collect and clean.

When these materials are wet, they won’t absorb moisture and don’t control odors.

Grass mixed with urine can also cause a pretty bad smell.

Soil

This is a good material for covering up odors.

However, when it mixes with urine, I found the soil becomes very mud-like and starts to smell.

Be warned – slushy toilet waste is an absolute nightmare to clean up!

What Makes A Good Cover Material?

All compost requires a carbon source. Carbon provides energy to the microorganisms that break down the organic matter. The amount of and type of carbon you use is particularly important if you want fast compost.

Covering materials, or brown materials, are that carbon source in a composting toilet and, therefore, should be carbon-based.

Carbon-rich materials you can use in your garden compost include dry leaves, pine needles, sawdust, paper, cardboard, twigs, straw, and dryer lint.

Some of these are great for composting toilets, and some are not. When picking a good brown material for a composting toilet, moisture and odor control become extra important factors.

Another consideration is how easy the resource is to work with. If it’s too fine, then it can get very messy, especially if you spill some.

I’ve found that the best cover material for composting toilets tends to be a mix of two different things because you get the benefits of both.

You can use a fine material such as peat for controlling odors mixed with a bulkier material to stop it from becoming too compact, which can block air from getting into the mixture.

Sun Mar’s recommended ratio is:

  • 60% organic bulking material (wood shavings, coir, chopped straw, or hemp)
  • 40% peat moss

Using a mixture also means you get a more diverse finished compost in terms of the microbes present. Great if you want to make some compost tea!

Where Can I Get Cover Materials From?

One of the best things about brown materials is that they can be free depending on where you get them. Many of the resources I suggest using are waste products from an already established industry.

The most economical and eco-friendly thing to do is use stuff you already own. However, they don’t always make the best cover materials, and this can get hard in winter when the materials might be scarce.

So, here are three other ways you can source suitable composting materials for your toilet:

Source them yourself from local farms or mills

This is the cheapest option and a great way to utilize local resources. It also helps small businesses make sure leftovers aren’t going to waste.

However, this might not always be possible, depending on where you live.

In our experience, local farms can’t always guarantee a consistent supply or consistent quality.

Buy them online or from local pet or garden stores

Stores might market these products for a different purpose, such as animal bedding, but they’ll often also work perfectly well as a cover material.

While this may be more expensive, you can ensure the supply of this resource, and it’ll generally be the same quality each time.

A downside to both these methods is that they are DIY options.

You may find yourself having to source two different things to mix together to get a perfect consistency.

Buy a pre-formulated mix

If you’re not into doing it yourself and prefer something you know will work out of the box, then you can buy a ready-made mixture that has been specially formulated for use as a cover material for a composting toilet.

This peat and hemp mix from Sun-Mar is the best one I’ve found.

How Much Cover Material Should I Use?

You shouldn’t have to use much brown material, just enough to cover the waste.

If you find yourself having to use a lot at once, this could be a sign it’s not very good at odor control.

It also means your toilet will fill up a lot quicker and need to emptied more frequently, adding to your chores list!

In this situation, I suggest swapping to a bulkier material as these tend to let odors escape, or mix your material with something else with better odor control.

Peat moss and coco coir are particularly good at fending off odors.

A Must-Read For Anyone With A Composting Toilet

If you’re serious about making your composting toilet the best it can be, I highly recommend reading Humanure Handbook by Joseph Jenkins. The book is an absolute goldmine of useful information about everything imaginable to do with composting toilets.

Humanure Handbook

If you want to skip all of the guesswork and potentially unwanted sticky situations, I recommend signing up for a completely free trial of Amazon Kindle Unlimited where the book is available without charge.

The book has a wealth of information and actionable tips on choosing the best cover materials for your exact setup. As well as this, the book covers every topic imaginable surrounding composting toilets and how best to manage them.

If you’re able to digest the book in less than a month, you can cancel your trial without any further costs. Win-win.

Summary

Transitioning to a composting toilet is definitely an adventure and one that calls for experimentation.

Picking a cover material is one of those experiments.

You might have to try a few options on our list before you find a formula that works for you – but don’t give up!

Interested in how to use the compost from your toilet? Check out our guide for some quick and actionable ideas.

About Veronica Fletcher

Veronica has a passion for all things eco-friendly. After growing up on a farm in Ireland, she went on to study Chemistry and Environmental Sciences. Veronica has also volunteered in many sustainability roles, including conservation efforts in Bangladesh and teaching Environmental Sciences to schoolchildren in Kenya.