How to Load a Rock Tumbler: Rocks, Grit, Water and Media
How full to fill a rock tumbler, how much grit per pound, how much water to add, when to use ceramic media, and how to avoid leaks and bruised stones.
Photo: Linas Juozėnas, CC BY 4.0In this guide
Short answer: fill a rotary tumbler barrel about half to two-thirds full with rock, add about 2 level tablespoons of grit per pound of rock, and add water until it’s just below the top of the rocks. If you don’t have enough rock, top up with ceramic media. Close the lid carefully, clean the rim first, and check for leaks before you leave it running.
Quick reference
| What | How much |
|---|---|
| Rock | Barrel about 1/2 to 2/3 full (some manufacturers say up to 3/4) |
| Grit (rotary) | About 2 level tablespoons per pound of rock, each stage |
| Grit (vibratory) | About 1/2 tablespoon per pound |
| Water | Just below the top of the rocks |
| Rock size | About 1/4 to 1 1/2 in (0.5–4 cm), mixed |
The Tumbling Planner works out the grit for your barrel size and the dates for each stage.
How full should the barrel be?
The stones need to roll and slide over each other. That’s what grinds them.
- Too empty: stones fall and crash instead of rolling. You get chips and white bruise marks.
- Too full: stones barely move, and the grinding is slow.
About half to two-thirds full is the common recommendation. Rocks lose size as they tumble, so a barrel that starts at two-thirds may be closer to half by the end of the coarse stage. That’s when ceramic media helps.
How much grit?
About 2 level tablespoons of grit per pound of rock is the standard rule for rotary tumblers, and the same amount is used in each stage. A 3 lb barrel therefore takes about 6 tablespoons per stage.
- More grit doesn’t make it faster. It mostly makes thicker sludge.
- Use fresh grit each stage. Used grit has broken down and lost its cutting power.
How much water?
Add water until it’s just below the top layer of rocks. Water carries the grit between the stones and cushions them.
- Too little: a thick paste that doesn’t grind well and can build up gas pressure.
- Too much: the grit is too diluted to work well.
When to use ceramic media
Ceramic media are small, hard ceramic pieces that you add to the barrel.
- Top up a barrel that doesn’t have enough rock.
- Cushion fragile stones like crystalline quartz.
- Carry grit into crevices and help even out the action.
Media can be reused, but clean it as thoroughly as the rocks between stages.
Close it properly
- Wipe grit off the barrel rim and the lid seal before closing. Grit in the seal is the most common cause of leaks.
- Close the lid firmly.
- Run the tumbler for a few minutes and check for drips.
- Open the barrel every few days during the coarse stage to let any gas out and check on the stones.
Frequently asked questions
How full should a rock tumbler be?
About half to two-thirds full of rock, topped up with ceramic media if needed.
How much grit do I put in a 3 lb tumbler?
About 6 level tablespoons per stage (2 tablespoons per pound).
Should rocks be covered with water?
Almost. Fill to just below the top of the rocks.
Why is my tumbler leaking?
Usually grit on the barrel rim or lid seal, or a worn lid. Clean the seal and rim before closing, and replace worn lids.
Next step: read the full grit schedule or start with rock tumbling for beginners.
