Choosing an abrasive comes down to one question before all others: is your abrasive harder or softer than the substrate? Get that wrong and there is no going back — the surface is marked.
Hardness first, grit size second
This is the most common misconception. Faced with a fragile substrate, the instinct is to reach for a finer grit. But fine garnet is still garnet: it will scratch polished marble every time. You step down in hardness first, and only then in grit size and pressure.
The scale is easy to remember. Garnet is the hardest in the range — the abrasive for metal, for stripping, for taking a surface back to bare. Calcium carbonate and sodium bicarbonate are considerably softer: these are the heritage abrasives, for stone and finished surfaces. Between them, crushed glass and glass beads each have their place.
Sodium bicarbonate is a salt. Absorbed into porous stone, it can swell roughly eightfold as it dries, breaking the stone apart from within. The damage does not show on the day of the job — it shows weeks later, once you have left.
Baking soda is for non-porous surfaces: polished marble, granite, glass, stainless steel, composites. On porous stone, use calcium carbonate.
Grit size governs speed, not quality
Coarse grit removes quickly and leaves a rough surface. Fine grit works slowly and leaves an even one. The trap is assuming fine is always « safer »: on thick paint or mill scale it will remove nothing, and the operator will raise the pressure until the substrate suffers.
The right method is the opposite: the coarsest grit the substrate will take, at the lowest pressure that produces an effect.
Dry or wet
Water suppresses dust, and it is often what makes a job possible at all — in a city centre, on an occupied site, on heritage work. It also softens the abrasive’s action.
But not everywhere: wood and metal are worked dry. One swells, the other rusts.
Testing an area is not a beginner’s precaution
Two stones bearing the same name, from two different quarries, behave differently. Structural timber from 1850 does not behave like the same species laid last year.
So you always start in an inconspicuous corner, at the lowest pressure that produces an effect, and work up gradually. You never work back down from too much pressure — by then the damage is done.
What we supply
Garnet in several grit sizes, calcium carbonate, sodium bicarbonate, glass beads, crushed glass and plant-based media. Delivered across Canada, by the bag or by the pallet.