We often get asked the question of which grit should I use. We stock two types of grit, relcaimed aluminium oxide and sintered aluminium oxide. Sintered aluminium oxide (or FastBlast) is heat treated aluminium oxide which looks like small ball bearings. These ball bearings are denser than the reclaimed oxide which means that they blast more granite out each time they hit the stone compared to normal reclaimed oxide (which is why they call it FastBlast). The other advantage of FastBlast is its extended life over reclaimed oxide. When the sintered oxide strikes the stone it chips small particles off the side of the ball rather than splitting into 2 roughly equal parts like the reclaimed oxide.
Once you have decided on what type of grit to use the next question is how coarse the grit needs to be. The larger particles in the grit are capable of creating a flat bottom to blasted surfaces, the smaller particles are capable of getting into the corner of letters and they also smooth the blasted surface. Grit is always blended from a variety of different size particles, 40/70 grit has a mix of particles from grade 40 up to grade 70. The larger the grade number, the smaller the particles (much like polishing discs). For general lettering we would recommend 40/70 FastBlast. The larger particles in this blend create a flat profile to the bottom of letters whilst the smaller particles are small enough to reach the corners in most serifs. If you are blasting photoblast stencils then we would recommend using 180-220 reclaimed aluminium oxide.
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