6 Best Silicon Carbide Grits For Stage One Coarse Grinding

There is a distinct, satisfying rhythm to rock tumbling that begins long before a stone reveals its hidden polish. The secret to a professional-grade finish lies entirely in the heavy lifting performed during stage one, where the rough edges are surrendered to the abrasive force of silicon carbide. Selecting the right grit is not merely about brand loyalty; it is the fundamental decision that dictates how much time and effort will be required to transform jagged creek finds into smooth treasures.

08/26/2026 08:32 am GMT

Disclosure: As an Amazon Associate, this site earns from qualifying purchases. Thank you!

Polly Plastics 60/90 Grit: Best Overall Choice

Polly Plastics 60/90 serves as the gold standard for those who want a consistent, predictable breakdown of rough rock. Its uniform particle size ensures that the grinding process remains steady throughout the entire cycle, preventing the dreaded “stalling” that occurs when lower-quality grits break down too quickly.

This grit is the ideal choice for someone running a standard rotary tumbler who values efficiency above all else. It strikes the perfect balance between aggressive cutting power and the structural integrity needed to survive a multi-day grind. If the goal is a reliable, high-performing baseline, look no further than this option.

Lortone 60/90 Coarse Grit: Most Reliable Option

When consistency is the primary objective, Lortone remains the industry benchmark. This grit is specifically formulated to maintain its sharpness over extended run times, making it a favorite for those processing harder stones like agates or quartz.

Relying on Lortone means fewer mechanical surprises and a more predictable slurry density inside the barrel. While it may carry a slightly higher price point, the reduction in wasted time makes it a smart investment for serious hobbyists. Choose this if the current batch contains exceptionally hard material that demands a durable, unwavering abrasive.

National Geographic Stage 1: Best Starter Grit

National Geographic provides a straightforward entry point for beginners who are just starting to curate their first collection of tumbling rough. It is packaged with accessibility in mind, stripping away the complexity of choosing between various grit grades by providing exactly what is needed for the initial cycle.

This option is perfect for those utilizing smaller, entry-level tumblers typically found in starter kits. It is designed to be forgiving and easy to work with, ensuring that the learning curve for stage one remains manageable. For the novice rock hound looking for a stress-free introduction to the craft, this is the most logical starting point.

MJR Tumblers 60/90 Silicon Carbide: Best Bulk

For those who treat rock tumbling as a high-volume activity, MJR Tumblers offers the most practical bulk solution on the market. Buying in larger quantities drastically reduces the cost per pound, allowing for continuous operation without the constant need to restock small, overpriced canisters.

The quality of the silicon carbide remains high even when purchased in larger volumes, ensuring that large batches of stone receive uniform treatment. This is the preferred choice for enthusiasts running multiple barrels simultaneously or processing large, heavy loads of raw material. If the workbench is never empty, this bulk format provides the best value and logistical ease.

Dan&Darci Step 1 Coarse Rock Grit: Top Value

Dan&Darci provides an excellent middle ground, offering a balance of quality and affordability that appeals to budget-conscious adventurers. It performs its primary function of smoothing rough edges effectively without unnecessary additives or complex branding that inflates the cost.

This grit is particularly well-suited for families or casual hobbyists who want to see results without a significant financial commitment. It is robust enough to handle standard tumbling rocks while remaining gentle on the wallet. Opt for this if the intent is to maximize the number of batches completed within a specific budget.

Covington 80 Grit Silicon Carbide: Pro Pick

Covington represents the tactical choice for the advanced tumbler who understands the nuances of grit sizing. By utilizing 80 grit rather than the standard 60/90 blend, the user gains a more aggressive initial cut that is essential for shaping difficult or deeply fractured stones.

This is a professional-grade abrasive designed for those who have mastered the basics and are now looking for precision. It requires careful monitoring to ensure the stones do not break down too quickly, but the control it offers is unmatched. If the objective is to achieve a specific shape or remove deep surface imperfections, this is the precise tool for the job.

How to Match Coarse Grit to Your Rough Stones

Matching grit to rock hardness is a fundamental skill that prevents uneven wear and excessive material loss. Harder stones like jasper or obsidian benefit from the aggressive cutting power of a coarser 60 grit, which helps to round out sharp corners efficiently. Conversely, softer stones require a lighter touch to prevent the material from grinding away entirely before the shape is even established.

• Hardness 7 (Quartz, Agate): Utilize 60 or 80 grit for maximum material removal.
• Hardness 5-6 (Fluorite, Sodalite): Opt for a 90 grit or a lighter charge to prevent structural damage.
• Mixed Batches: Always prioritize the hardness of the softest stone in the barrel to avoid turning that material into useless sludge.

Essential Tips for Achieving the Perfect Slurry

The slurry—a mixture of water, rock dust, and grit—is the actual medium that does the polishing work. A slurry that is too thin will fail to carry the grit against the rock faces, while one that is too thick can impede the tumbling action entirely. Aim for a consistency similar to thick pancake batter or heavy cream to ensure optimal contact.

If the slurry appears too watery during the mid-cycle check, consider adding a small amount of extra grit or a filler like ceramic media. Ceramic media is particularly useful in absorbing the impact of larger stones, protecting them from bruising while helping to maintain the necessary density of the slurry. Always ensure the barrel is filled to the manufacturer’s recommended level to allow for proper movement.

Knowing When to Move from Stage One to Stage Two

The transition from stage one to stage two is perhaps the most critical decision in the entire process. The goal of stage one is to remove all major chips, pits, and saw marks; if these are not removed now, they will persist through every subsequent stage. The stones should appear uniformly frosted and smooth to the touch before the barrel is emptied.

Do not be tempted to rush this process based on a set number of days. If the stones still exhibit deep craters or jagged edges after a week, wash them thoroughly and reset the barrel for another cycle in stage one. Moving to stage two prematurely results in a matte, dull finish that will never achieve a true, high-gloss shine.

Proper Storage to Keep Your Silicon Carbide Dry

Silicon carbide is hygroscopic, meaning it has a tendency to absorb moisture from the air if left in humid conditions. When grit becomes damp, it clumps together, making it difficult to measure accurately and reducing its abrasive efficiency. Always store grit containers in a cool, dry place, away from the immediate moisture of the tumbling area.

Consider using airtight plastic bins or glass jars with rubber gaskets to keep the grit completely isolated from the environment. Proper storage not only preserves the cutting power of the abrasive but also prevents the creation of “grit cakes” that are a nuisance to break up. A well-organized, dry storage system is the hallmark of a prepared and efficient rock tumbling setup.

Whether you are seeking the perfect shine on a piece of mountain-found quartz or simply looking to enjoy the therapeutic cycle of a rotary tumbler, starting with the right silicon carbide grit is the key to success. By selecting the grade that matches your material and your patience, you ensure that every hour the barrel spins is time well spent. Remember that the best results are rarely the result of a single, lucky run, but rather a commitment to the process and an attention to detail that begins with the very first pound of grit.

Frequently Asked Questions (FAQs)

What does silicon carbide grit do in stage one coarse grinding?

Silicon carbide grit shapes rough stones by rapidly wearing down jagged edges, smoothing pits, and rounding rock corners during stage one coarse grinding. Because silicon carbide rates at a 9 to 9.5 on the Mohs hardness scale, the grains fracture into fresh sharp points continuously during tumbling. This aggressive cutting action levels surface flaws on hard materials like agate and jasper before fine grinding begins. Inspect your rough batch weekly to confirm all sharp corners have fully rounded before moving forward.

What mesh size is coarse silicon carbide grit for tumbling rough rocks?

Coarse silicon carbide grit for tumbling rough rocks typically ranges from 36 to 90 mesh, with 60/90 mesh being the standard industry choice. A 60/90 blend contains particles that pass through a 60-mesh screen but catch on a 90-mesh screen, measuring roughly 177 to 250 microns across. Extremely hard or large rocks over two inches wide often require an extra-coarse 36 or 46 mesh to remove deep matrix rock quickly. Beginners should start with graded 60/90 grit for dependable shaping on standard Mohs 7 stones.

How do you add silicon carbide grit during stage one coarse grinding?

Loading silicon carbide grit requires placing rough rocks into the barrel first, pouring the measured abrasive over the batch, and adding water just below the top layer. Fill the rotary tumbler barrel between two-thirds and three-quarters full of rough stones sorted to similar hardness levels. Measure out your grit according to barrel capacity, seal the barrel lid tightly, and verify the outer rim is dry to prevent slipping on the motor rollers. Always check the barrel pressure every two days during this active gas-releasing phase.

How long does stage one coarse grinding take with silicon carbide grit?

Stage one coarse grinding with silicon carbide grit usually takes between seven and twenty-one days of continuous rotary tumbling. Silicon carbide breaks down into tiny, ineffective mud particles after about seven days, meaning the barrel must be cleaned and recharged with fresh abrasive weekly. Softer materials like obsidian round out in seven to ten days, whereas dense minerals like petrified wood or quartz often require three full weekly cycles. Repeat the weekly coarse run until no chipped faces remain.

Silicon carbide vs aluminum oxide which is better for stage one coarse grinding?

Abrasive testing proves silicon carbide is significantly better than aluminum oxide for stage one coarse grinding because it cuts faster and fractures into sharp edges. Measuring 9.5 on the Mohs scale, silicon carbide grinds hard stones much faster than aluminum oxide, which rates at Mohs 9.0 and tends to round over rather than shatter cleanly. Aluminum oxide works best in prepolish and final polish stages where delicate, burnishing friction is preferred over rapid bulk stock removal. Choose silicon carbide whenever you need to carve down rough jagged rocks.

How much silicon carbide grit do you put in a 3-pound rock tumbler barrel?

Two to four tablespoons of coarse silicon carbide grit is the standard amount needed for a three-pound rock tumbler barrel during stage one. Using roughly two level tablespoons per pound of stone ensures adequate rock-to-grit contact without clogging the slurry. Adding excess grit does not speed up shaping; unground particles simply cushion impacts and waste money. For a standard three-pound batch containing two pounds of rock, four tablespoons of 60/90 silicon carbide provides optimal grinding power for a seven-day run.

Why are rocks still sharp after running silicon carbide coarse grinding grit for a week?

Rough stones remain sharp after a week if the silicon carbide grit broke down completely or if the tumbler barrel was underfilled. Underfilled barrels allow rocks to crash violently without creating the rubbing friction required for abrasion, while overfilled barrels prevent rocks from tumbling over the crest. Silicon carbide also disintegrates into round silt after five to seven days, halting any further shaping. Clean the barrel completely, refill stones to the two-thirds mark, and add fresh coarse grit to restart effective grinding.

Is silicon carbide grit safe to wash down household sink drains after coarse grinding?

Rinsing silicon carbide grit slurry down household sink drains is never safe because the heavy mineral sludge hardens inside plumbing traps like concrete. Water will not dissolve ground silicon carbide or rock flour, causing the dense suspension to settle at the lowest points of household pipes. Always wash coarse-ground stones outside inside a plastic bucket or dump rinse water into a shallow trench in your garden soil. Let the bucket settle overnight, pour the clear surface water onto grass, and throw the thick sediment into household trash.