Limestone is one of the most forgiving carving stones available, which is exactly why beginners underestimate it. The softness that makes it approachable also makes it easy to over-cut, and the porosity that gives it a warm, matte finish means it absorbs stains and moisture in ways that can ruin months of work if you are not careful.

I carve limestone regularly, mostly Oamaru stone from New Zealand and various Australian limestones. It is a wonderful material when you understand what it is and what it is not. Here is what I have learned from years of getting it right and getting it wrong.

What Limestone Actually Is

Limestone is a sedimentary rock composed primarily of calcium carbonate, usually from the accumulated remains of marine organisms. Shells, coral fragments, and microscopic foraminifera compressed over millions of years. This biological origin gives limestone its characteristic grain and porosity.

The hardness varies enormously. Oamaru stone is so soft you can carve it with woodworking tools. Indiana limestone, the classic American building stone, requires proper stone chisels and more effort. Portland stone from England is harder again. Knowing where your stone sits on this spectrum determines your entire tool selection.

Choosing Your Block

Look for consistent colour and grain. Hold the block up to light if it is thin enough, or wet a surface to see the internal structure. What you want to avoid are hidden bedding planes, which appear as faint lines running through the stone. These planes represent boundaries between depositional layers, and the stone will split along them under stress.

Tap the block with a steel hammer and listen. A clear, ringing tone means solid stone. A dull thud suggests internal fractures or voids. This is not foolproof, but it catches the obvious problems.

Buy more stone than you need. Limestone is relatively inexpensive compared to marble or granite, and having spare material means you can test your approach before committing to the main block.

Tools and Technique

For soft limestones like Oamaru, riffler rasps, surforms, and even coarse sandpaper remove material efficiently. A coping saw can cut basic profiles. This accessibility is what makes limestone excellent for teaching and for sculptors transitioning from other materials.

For medium-hardness limestones, tungsten carbide-tipped chisels work beautifully. The stone parts cleanly with moderate mallet force. Point chisels for roughing, tooth chisels for shaping, flat chisels for finishing. The classic progression that has not changed in thousands of years.

Keep your chisels sharp. Limestone is soft enough that people neglect their edges, but a dull chisel crushes the surface rather than cutting it, leaving a bruised texture that is visible after finishing. Five minutes on a grinding wheel between sessions saves hours of sanding later.

Common Mistakes

Mistake one: ignoring the bed. Sedimentary stones have a natural bed, the orientation in which they were deposited. Carving against the bed can cause flaking and delamination. For architectural work, stone should be set on its natural bed. For sculpture, understanding the bed orientation helps you predict where the stone might want to split.

Mistake two: rushing the finish. Limestone’s softness makes it tempting to skip sanding grits. Do not. Moving from 80 grit straight to 400 leaves scratches that show up under raking light. Work through 120, 180, 240, 320, and 400. Each stage matters.

Mistake three: leaving limestone unsealed outdoors. Limestone is porous and absorbs water readily. In freeze-thaw climates, this water expands and spalls the surface. Even in Australia’s milder climate, moisture absorption leads to biological growth, staining, and gradual erosion. If your work is going outside, seal it with a breathable stone sealer. Not a surface coating that traps moisture, but a penetrating silane or siloxane sealer that lets vapour escape while repelling liquid water.

Mistake four: underestimating weight. Limestone is lighter than granite or marble, but a half-metre cube still weighs around 170 kilograms. Plan your lifting and moving strategy before you start carving, not after.

Mistake five: working dry. Limestone dust is calcium carbonate, and while it is less hazardous than silica-containing dusts, it still irritates lungs and eyes. Work wet when possible, especially with power tools. When working dry, wear a P2 respirator.

Finishing Options

Limestone accepts several finishes. A rubbed finish using progressively finer grits gives a smooth, matte surface that shows the stone’s fossil content beautifully. A tooled finish, leaving visible chisel marks, suits architectural and monumental work. A polished finish is possible on harder limestones but rarely achieves the mirror gloss of marble.

For indoor work, a light application of beeswax deepens the colour slightly and provides some protection against handling marks. Apply it thinly with a soft cloth and buff gently.

Sourcing in Australia

Australian limestone is available from several quarries. The Gambier limestone from South Australia is a reliable carving stone. Various Queensland limestones appear in the building trade and can sometimes be sourced as offcuts. Oamaru stone from New Zealand ships to Australia regularly through specialist suppliers.

Talk to your local stonemason or monumental mason. They often have offcuts and reject blocks available at reasonable prices. A block that is too fractured for a headstone might be perfectly fine for a sculpture where the fracture line becomes part of the design.