I am finishing my basement. I want to put laminated flooring on part of the basement and 12' vinyl tiles on some. I have noticed a couple of small bumps, or high spots in the concrete. They are barely noticeable when looking at the floor, but are very noticable if you lay a level across them. They are perhaps 4-5 inches around, rising to perhaps 1/4 inches. I tried using my belt sander with a 50 grit belt and it only scored the surface. Can I get a belt that will flatten these bumps? What else can I try?
Basements usually have a pretty high moisture content in the concrete.
Do a cheap moisture test. Tape down one or more 2'x2' sheets of clear plastic (duct tape the whole perimeter of the sheet). Wait a week. If the concrete turns dark and/or beads of moisture build up on the plastic, don't do laminate.
As far as lumps in concrete go, I like a 40lb demolition hammer... If you don't have one, a short-handled sledge hammer (3lb or so) and chisel will do the trick, albeit more slowly. Basically, you chip the lump into a depression and float it level with the rest of the floor with some patch after you're done.