This project was built and designed by Mike Montgomery from Modern Builds.
Mike set out to build a custom terrazzo sit-stand desk using desert jasper, a rare and colorful stone found only in a remote region of Madagascar. He sourced the material from several different suppliers, ranging from bulk bags of rough gravel to pricey polished specimens, in order to compare quality and figure out what he’d recommend to other makers interested in trying the stone for themselves.
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Sourcing and Cutting the Desert Jasper
Desert jasper looks fairly plain on the outside, but Mike found that slicing into the rough stones revealed dramatic streaks of blue-gray, blood red, and earthy brown. Using a basic wet tile saw meant for cutting backsplash tile, he trimmed the irregular stones down and sliced them into thin show slabs, learning along the way that buying rough stone is a gamble since there’s no way to know what the interior will look like until it’s cut open.
Some of the specimens he purchased delivered exactly the color mix he was hoping for, while others leaned more heavily toward blue tones than the earthy hues he wanted. He also compared the cost-effectiveness of cutting his own slabs versus buying pre-cut slabs or finished specimens, concluding that cutting your own is a smart way to save money if you already have the tools for it.
Prepping the Aggregate
Beyond the show slabs, Mike worked through bags of loose desert jasper gravel, cutting many of the larger pieces in half to expose more of the colorful interior and give himself more usable show faces for the pour. Smaller pieces that were too tricky to cut were broken down with a sledgehammer inside a sealed bag, turning the leftover chunks into fine aggregate for the concrete mix.
This aggregate prep step took more effort than expected since the stone turned out to be exceptionally hard, but it paid off with a good range of aggregate sizes, from fine dust to small and medium chunks, all ready to be incorporated into the terrazzo mix.
Building the Mold
To create the desktop, Mike built a simple melamine mold sized for a large sit-stand desktop, using a circular saw and straight edge to break down the panel into a bottom piece and side walls. He pre-drilled and screwed the pieces together with pocket screws that have flat heads, which made them ideal for mold-building instead of typical tapered wood screws.
A heavy coat of paste wax was worked into every seam and corner of the mold to keep it watertight and to ensure the cured concrete would release cleanly. He also cut sections of rebar to reinforce the slab, sizing them to run nearly the full length of the desktop for added strength.
Mixing and Pouring the Terrazzo
Before pouring, Mike arranged his best show slabs and halved gravel pieces face-down in the mold, since the bottom of the mold becomes the top surface of the finished desk. He aimed for a natural, non-gridded layout, clustering some pieces together and spacing others out to keep the pattern from looking too uniform.
The terrazzo mix followed a basic ratio of aggregate, sand, and Portland cement, and he supplemented the desert jasper with white marble chips as a filler that would blend in seamlessly if exposed during grinding. After running short on his first batch, he mixed additional batches to fully fill the mold, packed the aggregate down firmesly, embedded the rebar, and screeded the surface flat before knocking out air bubbles with a few taps from a hammer.
Grinding and Polishing
After letting the slab cure, Mike flipped the mold to reveal the top and began grinding back the surface to expose the aggregate underneath. He experimented with a few different grinding wheels and diamond polishing pads, comparing how aggressively each one removed material and how cleanly they exposed the stone without chipping it out.
One set of pads caused unexpected discoloration on the white concrete, so he switched back to a more familiar set of diamond pads he’d used on previous projects. Progressing through a wide range of grits smoothed out the surface scratches, and switching to a wet polisher for the finer grits made the process faster and helped bring out a deep polish on both the stone and the surrounding concrete.
Slurry Coat, Edges, and Finishing
To fill any remaining voids, Mike applied a wet slurry coat of cement and sand across the entire top, working it into the negative space before letting it cure and grinding it back again. He then shaped and rounded over the edges using an angle grinder fitted with a diamond bit, giving the desktop a clean, finished edge that matched the polished top.
For sealing, he chose a high-gloss lacquer-based sealer instead of the acrylic finishes he’d used on past terrazzo builds, applying several light coats to avoid pooling and to make the color of the stone pop. The finished top was then mounted to a motorized sit-stand base, giving the heavy slab the ability to move from a seated to standing height with the push of a button.
A Standout Addition to the Terrazzo Lineup
This build stands out among Mike’s terrazzo projects thanks to the striking color combination the desert jasper brought to the mix. The blend of cool blue-gray tones with warm earthy hues created a look he compared to a desert landscape, and the extra effort spent sourcing and prepping the stone clearly paid off in the final result.
For anyone interested in trying terrazzo with unique stone types, this project is a good example of how experimenting with different suppliers, cutting techniques, and grinding tools can shape the final outcome just as much as the design itself.
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Matt’s Take
These are my personal thoughts and tips based on my own experience in the shop. This section is not written, reviewed, or endorsed by the original creator of this project.
Terrazzo work like this is one of those projects that looks like pure artistry but is really a science experiment in disguise. Getting a good spread of aggregate sizes, from dust up to chunky pieces, is what gives a terrazzo surface that natural, layered look instead of a flat gridded pattern. If you’re thinking about trying something similar, it’s worth doing a few small test pours in disposable containers first so you can dial in your ratios before committing a full batch to a mold you can’t easily redo.
Cutting stone on a wet tile saw is a great budget-friendly approach, but it’s worth remembering that stone dust, especially from something as hard as jasper, can carry silica. A respirator rated for fine particulates and good ventilation go a long way here, even when you’re cutting wet. The water keeps dust down, but it doesn’t eliminate the risk entirely.
On the mold side, melamine is a smart choice since it’s naturally slick and won’t absorb moisture from the mix, but that heavy paste wax step really is what makes or breaks a clean release. Skimping there can mean a fight getting the slab out later, and concrete doesn’t forgive rough handling once it’s cured.
Grinding and polishing concrete is where patience pays off. Rushing through the grits or skipping steps tends to leave swirl marks that only show up once you’ve already sealed the piece. Working methodically through each grit, wet or dry, is what brings out that glassy, professional-looking shine at the end.