Render acting strange

[Baldmonkey]

Hi guys just a quick one, did a render about a month ago. Its one of my window customers, anyway she messaged saying will you have a look at the render when you clean the windows next as there is a lot of dust coming off... Normal i thought, you get some.. Anyway i took a picture and there is a lot of dust and risidual render coming off. This will be my 18th render clean and ive not seen this much come off before.. Is this normal or have you any thoughts, thanks

 

[Pjj]

Got any pictures ? Did you hypo it ? Is it the salt from the hypo coming off ?