Staining beneath window sills

[DeLaCruz]

I am assuming this is caused by metal in the window sills - its a common theme amoungst the estates i am cleaning at the moment. Hypo is not getting it off completely although sometimes it gets a bit off. On one house recently the hypo seemed to initially exaggerate the staining and it ran further down the wall! 

I have oxalic acid already but haven't used it yet - do any of you guys use it regularly and can offer some advice on safest and best way to apply. Is using it while the hypo is still freshly rinsed off the walls a bad idea ? 

I also added a picture of another stain i haven't seem before, the light brown that runs near the bottom of the wall and across the plastic electrical box - hypo didn't touch this either

 

[Pjj]

Always use the oxalic acid before hypo remove rust stains or lead Staines first rinse down thoroughly then apply hypo if needed , hypo will make lead Staines look much worse ,  we apply it using a brush or a hand sprayer , just mist the wall first with water then apply the oxalic , leave to dwell re apply if needed . 

 

[DeLaCruz]

Always use the oxalic acid before hypo remove rust stains or lead Staines first rinse down thoroughly then apply hypo if needed , hypo will make lead Staines look much worse ,  we apply it using a brush or a hand sprayer , just mist the wall first with water then apply the oxalic , leave to dwell re apply if needed . 

nice one thanks for that - yes the lead staining thing was quite a nervous moment haha, got it sorted but wanna be avoiding stuff like that and leaving my jobs sure everything looks tidy. Much appreciated for the advice, looks like ill be using this stuff on the regular for many of these jobs