Sir,
I have house plan for 22.5* 40. Max room size is 11*11. All room corners has columns. My mistri has 30 years of onsite experience in residential construction. I told him to use m15 in column footing and m20 in columns above plinth level. He said for above mentioned grades we need vibrator and concrete mixer which is not economical option for smaller plots having maximum span less than 16 feet. He told me to use 1:2.5:4 through out the columns upto 2 storey building as we needed to mix concrete by hand and if bajri is more then concrete will not get smooth.
1:2.5:4, or 1:3:3 or 1:3:4 is prevailing commonly in our area when I asked some other mistris.
He will be using mixer and vibrator for rcc slab only
What to do sir?