Rock Tumbling Grit: Your Questions Answered

If you've been searching around for answers on rock tumbling grit, you've probably noticed the same handful of questions keep coming up. I get asked these all the time too, so I thought it was about time I put the answers in one place. No waffle, just straight answers with a bit more detail underneath if you want it.

What can I use as grit in a rock tumbler?

You should always use purpose-made rock tumbling grit, either silicon carbide or aluminium oxide. This is because proper tumbling grit is manufactured to a consistent grain size for exactly this job, which is why it's worth using from the start.

I know the upfront cost for rock tumbling grit can look a bit steep initially, but it goes further than you'd expect. You only need a small amount per batch, so a single small tub typically covers several tumbles. If you'd rather not buy each stage separately, our grit bundles have all four stages ready to go in one go, which tends to work out better value overall.

What kind of grit to use in a rock tumbler?

The short answer: use silicon carbide grit for the coarse and medium stages, and a polish (like cerium oxide, aluminium oxide or pumice powder) for the final stage.

Rock tumbling is done in stages, and each stage needs a different type and grade of abrasive:

Coarse grit (stage 1) – shapes and rounds your rough rocks, knocking off any sharp edges
Medium grit (stage 2) – smooths out the scratches left by the coarse stage
Fine grit (stage 3) – refines the surface further, getting it ready for polish
Polish (stage 4) – this is where the shine actually happens, using a much finer compound rather than a grit as such

Some people also like to run a pre-polish stage, using a very fine silicon carbide such as F600 or F1200. Our Complete Grit Bundle comes with four grades of silicon carbide for this exact reason. 

Using the wrong grit at the wrong stage is one of the most common reasons rocks come out dull rather than glossy. If you want more detail on how each stage builds on the last, it's worth reading our full guide to the rock tumbling process.

How much grit do I put in a rock tumbler?

As a general rule, use around 1–2 tablespoons of grit per pound (roughly 450g) of rocks in your barrel. 

Too little grit and your rocks won't grind evenly, since there isn't enough abrasive doing the work. Too much, and you risk the opposite problem; the grit can't move freely around the barrel, which slows everything down and can even lead to uneven results. 

Can I reuse grit from a rock tumbler?

Absolutely not. once a batch of grit has done its job, it breaks down and loses its cutting power, so it needs to be disposed of rather than reused for the next stage.

This does get asked by beginners, because it feels wasteful to throw grit away after just one cycle, but grit is designed to wear down as it works. This means that by the end of a stage, the particles have broken into much finer pieces than when you started, which is actually part of why it's so important not to carry it over into the next stage (more on that below). Always start each new stage with a fresh batch, and give your rocks and barrel a proper clean in between. Check out our guide on grit contamination for tips on this.

Can you put too much grit in a rock tumbler?

Yes, overloading the barrel with grit can actually slow down your results and, in some cases, contribute to dull or scratched stones.

It may logical that more grit would mean faster grinding, but tumbling relies on your rocks and the abrasive tumbling freely against each other as the barrel rotates. If there's too much grit relative to the amount of water and rock, that movement gets restricted, and the grinding action becomes far less effective. Stick to the recommended ratios above rather than guessing on the generous side.