Rock N Soil Matte Black Iron Oxide Powder, Concrete Pigment Powder, Grout Colorant, Color Dye for Cement Stucco Plaster Mortar Paint Coating Wood Stain Putty Epoxy Resin - 5 Oz, Black

Why I keep this black pigment in the shop

I keep a small bag of black pigment around for the same reason I keep shims and painter’s tape: it solves problems fast. The Rock N Soil black pigment is one of those simple, dependable materials that can blend a mortar patch, darken grout, or turn a basic concrete pour into something that looks intentional. After using it across a handful of projects—grout color corrections, a cast-concrete planter, a limewash touch-up, and even a small batch of tinted epoxy—I’m confident calling it a versatile, straightforward pigment that behaves the way a good iron oxide should.

What it is and how it behaves

This is a matte black iron oxide powder with a fine 500-mesh grind (about 29 µm). In practice, that fineness matters: it disperses evenly without gritty specks and doesn’t fight the mix. It’s water-dispersible, which makes it easy to add to cementitious materials and waterborne coatings. The finish is opaque and matte, skewing toward a deep charcoal to black depending on dosage and binder color. It’s rated for interior and exterior use, and it plays nicely with other mineral oxides if you want to blend your own shades.

The 5 oz bag is a sensible size for small batches, color tests, grout work, stepping stones, and detail pieces. If you’re coloring a big slab or a long run of precast, you’ll either need multiple bags or to step up to a larger container of pigment.

Mixing and dosage

For concrete, a practical starting point is 1 part pigment to 20 parts concrete by weight. That yields a medium charcoal on gray cement; using white cement will give a cleaner, darker black at the same loading. If you want a deeper shade, increase the dose incrementally. I strongly recommend doing a small test puck (muffin tin or disposable cup molds work great) to judge the dry-down color—cement pastes always look darker wet.

A few mixing tips that have worked well:

• Dry blend first: For cement and grout, whisk the pigment into the dry components before adding water. The pigment disappears into the mix quickly and resists clumping.
• For epoxy/resin: Pre-disperse the pigment into Part A to a smooth paste before adding Part B. Start low; this pigment is strong, and too much can thicken the resin.
• For limewash and paints: Create a small pigment slurry with water, then add to your base. Strain if you’re chasing an ultra-smooth finish.

At moderate loadings I didn’t notice a meaningful impact on set time or strength in concrete. At very high loadings (beyond what I’d use for structural work), expect a small bump in water demand and a touch of stiffness. A splash of plasticizer is more elegant than adding extra water if you need flow.

Color results in different binders

• Gray cement concrete: Expect a handsome charcoal to soft black. If “jet black” is the goal, either push the dose or use white cement for cleaner results.
• Grout and mortar: It excels here. The color blends consistently, and it’s easy to tweak toward darker joints without the patchiness you get from on-surface stains.
• Limewash and plaster: The pigment yields warm, earthy blacks that read natural rather than inky. It integrates well and retains the matte, mineral character of the finish.
• Epoxy and coatings: In clear epoxy, it produces a solid, opaque black. The epoxy’s inherent gloss remains; the pigment itself doesn’t “matte” the surface—your topcoat choice drives sheen.
• Wood fillers and waxes: Great for tuning wood putty to match dark species or ebonized finishes. Because it’s opaque, a little goes a long way.

The black here leans neutral to slightly warm. If you’re used to the blue-leaning “carbon black” look, this iron oxide reads more natural. For many architectural uses—mortar, stucco, terrazzo—that’s a plus.

Durability and weathering

Mineral iron oxides are among the most UV-stable pigments available, and that’s consistent with my experience outside. The color doesn’t chalk or fade the way organic blacks can, and because it’s integral color (mixed into the matrix), it wears far better than topical stains. On exterior concrete that sees traffic, sealing will deepen the color and add some abrasion resistance; without a sealer, expect the surface to lighten a hair as laitance wears away.

Coverage expectations and batch control

The 5 oz size is perfect for small tasks, but it’s easy to overestimate how far it goes if you haven’t worked by weight before. At a 1:20 ratio, 5 oz tints roughly 6.25 lb of concrete mix to a medium-dark tone. That’s ideal for samples, small castings, stair treads, touch-ups, or a section of grout. For a full 60 lb bag of concrete at that same ratio, you’d be in the ballpark of 3 lb of pigment—so plan accordingly.

Batch consistency matters. Weigh your pigment and binder, keep water content consistent, and mix the same way every time. If uniformity across multiple pours is critical, make a standard slurry or pre-blend a larger dry batch so each pour draws from the same color lot.

Cleanliness and handling

It’s a fine black powder—expect it to be messy if you’re casual with it. A dust mask, gloves, and a damp towel nearby go a long way. It cleans with water, but it can tint porous surfaces, so cover what you don’t want colored. I decant the bag into a small, airtight jar with a spoon; it keeps the dust down and makes dosing cleaner.

What I liked

• Reliable dispersion: No speckling or streaks when dry-blended into cement and grout.
• Predictable, buildable color: Easy to scale from charcoal to near-black by weight.
• Versatility: Works across cementitious materials, limewash, epoxy, and fillers without fuss.
• Exterior-ready: Mineral stability and integral color hold up outdoors.

Where it could be better

• Packaging size: The 5 oz bag is great for small projects, but many users will need a larger option for bigger pours.
• “Jet black” expectations: On gray cement, even strong doses land more charcoal than absolute black. That’s normal for iron oxide, but worth noting. Using white cement or a black-tinted sealer closes the gap.

Practical tips

• Always do a test puck and let it cure fully; colors lighten as they dry.
• Weigh pigment and binder—don’t measure by volume if you care about consistency.
• For darker results on gray cement, consider a penetrating sealer or wet-look topcoat to deepen the final appearance.
• If you need very deep black with minimal loading, blend a small amount of carbon black with this iron oxide—but test first; carbon black can alter workability more than oxides.

Who will get the most value

• DIYers and makers casting planters, pavers, terrazzo, or countertops in small runs.
• Tile setters or homeowners adjusting grout and mortar color to match stone or tile.
• Finishers working with limewash, plaster, or stucco who want earthy black tints.
• Woodworkers and repair techs tuning fillers and epoxy for dark finishes.

Final take

The Rock N Soil black pigment has earned a permanent spot on my shelf because it’s consistent, easy to control, and genuinely versatile. It disperses cleanly, builds color predictably, and holds up outdoors—exactly what I want from an iron oxide. The 5 oz size is best suited to small batches and detail work, and if you’re chasing an absolute, ink-like black on gray cement, plan on higher loadings or pairing with white cement. Those caveats aside, it’s a dependable way to get integral, matte black coloration across a wide range of materials.

Recommendation: I recommend this pigment. It’s a reliable, straightforward black iron oxide that delivers consistent results with minimal fuss, especially for small to medium projects where integral color and durability matter. If you need to color large volumes, scale up the quantity or buy a larger size, but for everyday tinting and repairs, this bag does the job well.