First expose, then beat, next clean. But winter is not good.
Hanging on the balcony, rub, twist, like hand washing clothes. Rub each other. And beat the dust.
Use a vacuum cleaner to suck the dust, pick bulk cement lime by hand, if it isn't ok, try to break them up, and use vacuum cleaner to suck .
If it is alkaline, try white vinegar to neutralize
