We have efflorescence in two areas of our cinder block basement, which is completely below grade. Sloping the grade away from the house is very difficult due to existing driveways and patios. Internal french drains are pricey. I don't think it is a severe moisture problem because no water enters the basement. My crazy thought is to drill 1 in. holes in the top and bottom courses of block so that the holes go into each of the three cores of the block. Hopefully this would allow air to vent up through the cores and dry out the moisture. My main concern in trying this would be if the holes would weaken the blocks causing them to crack. Each area is about 8 ft. wide. Thanks

The areas where the efflorescence is, is it were the patios or driveway meets the house. If so, seal where these items meet the foundation.

Also check to make sure all your downspout leaders are draining away from the foundation. If you have underground gutter drains make sure the aren't blocked or damaged.