“I needed to grind a slab of 4000 psi, 6 month old concrete soI bought a set of extra soft 40/60 grit Magnatrap inserts for an Edco grinder. They cut great for about 30 minutes but then glazed over and stopped cutting. Then I got a set of extra soft 18/20 grit inserts and had the same thing happen. Brendan at the service line said that they usually suggested wire brushing the cutters or grinding something soft to erode the matrix and expose fresh diamond. The wire brush didn't work at all. Grinding a cinder block worked modestly well on the 18/20, but not at all on the 40/60. Even the 18/20 never did a very good job of removing material. I needed to go down about 1/32" to hit the low spots and never got there after several days of grinding on a 1500 sf slab.
In the end I had to give up on these cutters and resort to hand grinding the low spots with a 4" medium/fine grinding wheel that I also got from eDiamond. It took days and in that time that 4" wheel never glazed over and kept cutting. I'm pretty disappointed that the $100 sets for the big machine never did the job. Maybe they would work well on green or lower psi concrete, but they do not work on 4000 psi.”
