The simplest and best way is that if you have used the cement brush, you can only use the cement brush again, but the cement cannot be mixed with water. Go to the chemical store to buy 35 kilograms of phosphoric acid mixed cement, and mix it according to the ratio of 90 phosphoric acid and 10 cement. After blending, let the cement slag sink and brush it on the iron column with the clear liquid above. Remove the previously brushed cement before brushing, and don't remove the rust on the column. This rust reacts with phosphate cement to produce iron phosphate, which is a good antirust agent.
If the corrosion under the column is serious, phosphoric acid cement solution can be used to adjust the corrosion to a lake shape and brush it to the place with serious corrosion. Brush the cement solution several times after drying.