I'm a bricklayer and I specifically do repointing work for 80% of my job. I use a 4.5" angle grinder to grind out the masonry joints. It's very dusty, which is typically why the grinders overheat, but some seem to last slightly longer.

I used to buy cheap Mastercraft Canadian Tire grinders because more expensive grinders like Hitachi and Skil only lasted marginally longer, and getting the in-house brand from Canadian Tire means I can get a walk-in exchange on the spot. They recently switched to palm switches instead of a lock-on switch, so I got cheap Princess Auto grinders for the same walk-in exchange reason because they still have a lock-on switch.

Today, I opened a new-in-box grinder and grinded 1.5 hours before lunch, swapped blades and resumed grinding after lunch. It was 30C, so hot outside, but I still didn't expect it the bearing to lock up in just 45 minutes. The grinder saw just under 2.5 hours of runtime and that was enough to toast it.

I'm looking for a recommendation from any bricklayers or other people who use grinders in dusty hot environments on a grinder that can at least do a work-week at a minimum.

I usually run the grinders for 60 to 90 minutes nearly continuous and I put a heavy strain on them. I know it's hard on the equipment, but I'm an independant contractor pricing work by the job; running it hard earns me more money to the point where time matter more than preserving the grinder... but I'd like for the grinder to last more than a day, 1 a week is pretty reasonable.

I don't know if bringing 2 grinders up on my scaffolding and rotating between them for cooling would be a worthy strategy, but the mastercraft ones usually could do the job. I can't use a palm switch though, because I need to be able to switch my grip and keep it running. I lock it on and grind.

Last few years I keep 2 grinders in the truck, and exchange 1 at night when I burn one, but if the Princess Auto ones won't do a full day's work, I might need to keep 3 or 4 on hand in case I start burning 2 a day when the grinding is heavy. I don't know if any grinders can cope with heat and heavy dust, I don't mind paying for quality, but so far everything just burns out anyways.

Sorry if the post was a little long, just wanted to describe the use-case and my experiences in detail. Thanks in advance for any advice anyone has to offer.