Just when we thought we have done a nice looking wall with Ayaka...Look again...Oh no! rust spots! How? Why? So sure the highest quality primer had been apply. Actually this is very old concrete wall. Prior to applying Ayaka, it was just emulsion paint, and there was no sign of lye and rust. But because Ayaka is water-based material, when applied onto the wall, the moisture forced the residue from the concrete mix (maybe from sand which had been mixed with some tiny branches. This is one of the most common cases in old Asian construction especially when the mortar mix is not done with clean sand. When this happen, Don't panic. The moral behind this scenario is to always keep some remaining of the J-Wall mixture after application is completed. Don't wash away all the remaining even though it is just less than one teaspoon. Wait for a few days after the wall is completely dry, and see the overall effect. You will never know what would happen. Now, let's fix it.