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Rock Tumbling Grit: Usage, Types, Disposal & Substitutes

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Rock tumblers use various types of grit in the multiple stages of the rock tumbling process to shape, smooth, and polish the stones. Knowing how to use it, what type to use and what substitutes are available can make your life a lot easier. While your rock tumbler may come with some basic instructions, they are unlikely to explain much about grit.

The best and hardest rock tumbling grit is silicon carbide. The coarsest grit is used for shaping, while the finest is used for smoothing. Polishing compounds are used for shine. The grit should never be poured down the drain as it can be set like concrete. Sinterblast can be used as a substitute. 

Here we answer crucial questions about rock tumbling grit such as what it is, what it’s made of, whether it’s toxic if you can reuse it, what kind to use, how best to dispose of it, and what alternatives there are. This information will help you get the best results from your tumbler and improve your understanding of how the tumbling process works.

What Is Rock Tumbling Grit?
What Is Rock Tumbling Grit?

If you are interested in checking out the best tumbling grits you can find them by clicking here (Amazon links).

What Is Rock Tumbling Grit?

When you grind and polish stone by hand, you use sandpaper with grits of different coarseness. Sandpaper has many uses in the DIY sector, but its primary use is to shape and smooth rough edges and surfaces on various items made of wood, stone, or metal.

Rick tumbling grit does essentially the same thing without the hard manual labor of using sandpaper. It comes in different levels of coarseness, just like sandpaper, and at the fine end of the spectrum resembles talcum powder in texture. Rock tumbling grit is in the form of different-sized granules that you add to the tumbler.

It is an abrasive substance that grinds away at the surfaces and edges of the rocks in the tumbler until they are smooth and rounded. Rock tumbling grit is also sometimes referred to as tumbling media. 

What Is Rock Tumbling Grit Made Of?

Rock tumbling grit is usually made of silicon carbide, an artificial abrasive with a hardness of nine or more on the Mohs hardness scale. This is extremely hard as a diamond, for instance, is a ten on the Mohs scale. By contrast, many rough stones such as agates, petrified wood, and jaspers only have a hardness of around seven or less.

Therefore, the silicon carbide is significantly harder than the stones in the tumbler. It breaks into angular particles when crushed, giving it an abrasive edge with sharp points that can dig into the rocks. It is widely used in lapidary work, including gem cutting and rock tumbling, and is relatively inexpensive.  

The stuff you put into the tumbler specifically to polish the rocks in the final stage is usually made of cerium oxide, tin oxide, chrome oxide, or aluminum oxide. It is a form of grit traditionally referred to as a polishing compound and is extremely fine.

TIP: There are some key supplies and equipment you need to ensure your tumbled rocks come out looking smooth and shiny. Check out the article below:
GUIDE: Rock Tumbler Accessories, Equipment & Supplies

Is Rock Tumbler Grit Toxic?

Rock tumbler grit is not toxic, but that doesn’t mean it isn’t harmful. Silicates cause silicosis, a respiratory disease that frequently afflicts miners and others working with stone. Silicon carbide specifically can irritate the nose and eyes on contact.

Prolonged exposure to high levels of silicon carbide can cause pneumoconiosis, a chronic lung disease that reduces lung function and causes coughing, wheezing, and shortness of breath. People with pneumoconiosis also have an increased chance of contracting tuberculosis.

There is also limited evidence that it can cause cancer in animals. It is regulated by the Occupational Health and Safety Act in the US (OSHA) and is on the Hazardous Substances List.

The slurry produced in a tumbler consists of grit, water, and small particles from the tumbled rocks. When it dries out, it becomes silica dust, which can cause silicosis. 

This disease takes many years of exposure to appear because silica dust gradually scars the lungs. After all, it’s abrasive. Silicosis is incurable but entirely preventable using the proper respirator and other simple precautions such as washing the dust from hands and face and using and washing overalls.

BTW: Do you want to know more about rock and mineral identification? The books listed below are the best ones you can find on the internet (Amazon links):

Can You Reuse Rock Tumbler Grit?

The slurry that results from rock tumbling contains rock particles, dirt from the rocks, and even minute pieces of plant material. It is almost impossible to separate the grit from the rest. If the slurry contains bits of rock that are bigger than the grit, they will ruin the next batch of rocks you tumble.

It is much harder to get the same consistency with reused grit, and most rockhounds don’t believe that reusing grit is worth it. That said, reusing grit won’t damage the tumbler. 

Rockhounds that have tried reusing the grit usually rinse the slurry and allow the water to completely evaporate, leaving just the dry grit and all the particles from the previous load of rocks.

These particles can make reused grit less effective, which means more time in the tumbler for the next batch of rocks and more expenditure on electricity for you.

Also, the grit particles themselves break down in the tumbling process and may not have as many sharp edges and angles as they did previously, which translates to longer tumbling time.

TIP: Check out the detailed guide on reusing rock tumbler grit If you want to know more:
Can Rock Tumbler Grit Be Reused? You Should Know This

What Kind Of Grit To Use In A Rock Tumbler?

The three typically used standard grits for rock tumbling are 60-90 in the beginning, 150-220  in the middle stage, and 500 in the end. If the stones are very hard and larger, you can use 45-70 grit for faster grinding in the initial tumbling stage.

Stage one grit is coarser than that used in any other stage and is used to turn the rough into the size and shape you prefer. Depending on the hardness and size of the rocks, this process can take anywhere from a week to a few months.

In stage two, you use the 150-220 grit to smooth the rocks and remove surface cracks, pits, and large scratches. In this stage, the rough edges are also ground down significantly. The second stage can also take a week or more.

You use the finest grit, 500, to give the stones a polished look in stage three. Minor scratches and indentations are removed in this stage, and it is usually the shortest, from three days to a week. This stage does not shine the rocks but makes them very smooth.    

The final stage is the polishing stage, where you use a polishing compound to shine the rocks. Depending on the nature of the stones and the finish you want, it can take between a week and a month to complete.

In the polishing stage, you have to use plastic pellets together with the polishing compound to stop the rocks from scratching each other as they tumble.

TIP: It is always good to know what rocks can be tumbled together and how long it takes to tumble different types of rocks. Check out these two articles below to know more:
What‌ ‌Rocks‌ ‌Can‌ ‌Be‌ ‌Tumbled‌ ‌Together:‌ ‌Complete‌ ‌List‌ ‌With‌ ‌Tips‌
How Long Does It Take To Tumble Rocks? Values For Various Rocks

Best Rock Tumbling Grit

Best Rock Tumbling Grit
Best Rock Tumbling Grit

You should always buy grit from a reputable source and don’t be tempted to go cheap. Cheap grit resembles popcorn and is softer than better quality grit. It contains material that will break down much faster in the tumbler, meaning you will have to use larger quantities. 

You can always inspect the grit quality with a loupe – the magnifying tool that jewelers and rockhounds use to scrutinize stones closely. Good quality grit looks like tiny shards of crystal with lots and angles and sharp points. Silicon carbide grit is still considered the best rock tumbling grit.

Rock Tumbler Grit And Ceramic Tumbling Filler Media

Polly Plastics sells a highly rated rock tumbler grit kit and ceramic tumbling filler media (Amazon link) recommended by many Amazon customers. It is for single use in a fifteen-pound tumble or five uses in a three-pound tumble and contains a pound of 60-90 silicon carbide grit, a pound of 180-220 silicon carbide grit, and half a pound of 500 grit.

The polish is aluminum oxide, and there are one and a half pounds of non-abrasive ceramic fillers in the kit. It is compatible with all tumbler brands.

Dan & Darci Rock Tumbler Grit Refill Kit

The Dan & Darci Rock Tumbler Grit Refill Kit (Amazon link) is also highly rated by Amazon users. It has a four-step grit set and poly plastic pellets for the polishing stage with clear instructions on how to use it. This kit is also compatible with any rock tumbler.

TIP: Loading your rock tumbler with rocks and grit can be a challenging task. Check out the complete guide on rock tumblers loading in the article below:
Rock Tumbler Loading: How Much Grit & Rocks Do You Put In?

Rock Tumbling Grit Alternatives

Silicon carbide is the best substance for rock tumbling grit, but you can make your own grit if you have the time and patience. You have to use an alternative with a hardness of more than seven on the Mohs scale; otherwise, you will just be wasting electricity by running your tumbler. 

Chalcedony, quartz, jaspers, agates, carnelians, and petrified wood typically have a hardness of between six and a half and seven Mohs, seven for most. These are commonly collected rocks that you might wish to tumble. Forget about using beach sand; it is simply not hard or uniform enough.

You can try silica sand or sinterblast as alternatives to silicon carbide. The former can usually be obtained from sandblasting companies. The problem is what you save in the cost of the sand you will make up for in electricity costs because silica sand takes a few weeks longer to achieve the same effect as silicon carbide.

If you are polishing soft rocks such as calcite, fluorite, obsidian, or marble, silica sand may work, but it generally isn’t worth it. The other difficulty with silica sand is that the grain size must be uniform. If some sand particles are bigger than others, they will score the rocks with noticeably deeper grooves, defeating the object of tumbling.

Sinterblast is a brown, sintered aluminum oxide grit typically used in sandblasting. It is a better alternative than silica sand as it is harder and reusable but isn’t as hard as silicon carbide.

Other sandblasting media, such as crushed glass, are generally too soft for tumbling rocks, but sintered aluminum oxide works and has been proven in many industrial applications. 

Sinterblast can be used to polish petrified wood, agate, quartz, jasper, and many other stones. The coarse grits are eight, ten, twelve, or sixteen, but the finest goes up to two hundred and forty. It is available in thirty, thirty-six, and sixty grades for rock tumblers. 

Aluminum oxide can irritate the skin and eyes on contact, and inhalation can irritate the lungs, nose, and throat. Repeated exposure could result in lung damage.

Crushed and sintered fine bauxite ore is often used to replace brown fused aluminum oxide, and it has a Mohs scale hardness of nine. It comes in tiny spherical beads made of seventy-five percent aluminum oxide that can be used in rock tumbling, carving, etching, grinding, polishing, and lapidary work.

TIP: Sand is the abrasive material present when rocks are naturally tumbled in nature. So can you use sand as the grit alternative? Find out more in the article below:
Can You Tumble Rocks with Sand? Everything You Need to Know

How To Dispose Of Rock Tumbling Grit

Rock tumbling grit, or more accurately the slurry that contains the grit when you have finished tumbling, can be dumped in your yard away from plants you value. It can suffocate plants if they get too much of it, not because it is toxic but because it blocks their air. 

If you don’t want it to dry out and blow silica dust for you and your family to inhale on a windy day, put a layer of topsoil or garden dirt over it. It won’t harm the soil any more than sand. Do not attempt to dump it on public land, as there are still dumping laws to consider!

An alternative is to put the slurry in a shallow open bucket or similar container and leave it to dry out. When it has been reduced to the consistency of mud, scrape it into a hole in the garden and cover the hole with dirt.

Instead of dumping it in a hole in the garden, you scrape it into a plastic bin liner and put it in the trash. Just remember that if it is too wet, and you have it in large quantities, it will be heavy. You can also put the slurry into a plastic jar, old ice cream container, or something similar and throw it in the trash.

You can also pour the slurry over a gravel driveway as it will settle into the gravel, bind it and reduce the dust that gravel driveways are known for. This won’t work on a brick or concrete driveway.

Some people use the slurry as fertilizer for the garden, but you should dig it into the bed and not spread it too thickly. Also, don’t put it directly on the plant or too close to the stem.

You do not, under any circumstances, want to dump the slurry from your tumbler into the plumbing system! It won’t wash away and will cause blockages that can cost you dearly to clear.

It is almost like cement and can be used as a mortar with gravel to fill in potholes in the yard or cracks and crevices in driveways and stone garden walls.

Conclusion

Knowing how to use rock tumbling grit is essential for getting the best results from your tumbler. Understanding grit types, the various sizes, and the tumbling stages at which to use them will save you time and energy and increase the efficiency of the rock tumbling process.

Disposing of the grit in a manner that doesn’t clog your plumbing or pose a health hazard will save you unnecessary expenses and give you peace of mind.

TIP: Rotary tumblers spin the rocks around as though they are in a washing machine, while vibratory tumblers shake them up at high speed in one place. So which one to choose?
Rotary vs Vibratory Rock Tumbler: Which One To Buy & Use