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I'm cleaning up some mould around the home and I have some substance on my window sills which I'm not quite sure if it's dirt or mould.

I have read about using Vinegar to clean up mould, but an article I was reading awhile back said you shouldn't use Vinegar on certain things as it can eat away at it or something because it's acidic; I thought this may have been metal and/or painted substances but I may be wrong.

I know you shouldn't use it on granite, marble and natural stone, but was wondering if using it on the painted metal window sills is ok or should I use something like diluted Tea Tree Oil instead, or would that be too oily?

FYI I would be using White Vinegar.

Here is a pic of my window sills:

enter image description here

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    $\begingroup$ Why vinegar? Makes no sense except if you have limescale. Use your standard household detergent for hand dishwashing. $\endgroup$
    – Karl
    Jan 12, 2020 at 21:42
  • $\begingroup$ Because if it's mould I would like to kill it; detergent isn't going to do anything in that way. $\endgroup$
    – Brett
    Jan 12, 2020 at 21:45
  • $\begingroup$ Makes no sense, sorry. If you wash it off, it´s gone, dead or not. If you can keep it dry, it will stay clean, if it´s wet often, it will get mouldy again after some time either way. $\endgroup$
    – Karl
    Jan 12, 2020 at 22:49
  • $\begingroup$ You do realise that once you start agitating mould it can start releasing "spores" - I'd say if you're killing it off first then this mitigates this risk; why would you clean with something that doesn't kill mould when you can clean with something that does!? Sure, if the surface gets moist again, mould could come back, but not wiping the surface down with something to kill what's already there would dramatically decrease the chance of it coming back without those conditions. $\endgroup$
    – Brett
    Jan 12, 2020 at 22:57
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    $\begingroup$ There are commercial multi-surface cleaners based on quaternary ammonium surfactants. These surfactants are bactericides and tend to prevent reoccurrence of the infestation simply from the tiny residue after wiping off. None of the items mentioned so far are so aggressive that they will hurt your windowsills. (But you could try new agents on one sill at a time and if it begins to suffer, don't use it on all the rest.) $\endgroup$
    – James Gaidis
    Jan 14, 2020 at 22:18

1 Answer 1

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Avoid aluminum alloys when working with vinegar solutions!

With time, the pH effect of acetic acid can penetrate the protective oxide coating. The exposed Al will even react with water:

2 Al (s) + 6 H2O (l) --> 2 Al(OH)3 + 3 H2 (g)

and with the presence of alloy metals, galvanic corrosion (especially if the 'dirt' is rich in salts that can serve as a good electrolyte) which apparently accelerates the attack on the Aluminum.

To quote a source:

corrosivity environment for aluminium in food industry are foodstuffs with pH 3 – 5, such as fruit juices, jams and acidic canned fruits or hot gravies, sauces as well as dressings, vegetables and fish pickled in brines with 1 –3 % salt [1]. In particular, acetic acid needs to be taken into corrosion consideration, due to its wide usage in food industry (vegetable and fish pickling), and its representative properties among acids and juices in fruits, vegetables and other organic materials that can corrode metals. Although aluminium has a good resistance to acetic acid solution at room temperature, aluminium can corrode in almost any concentration of acetic acid at any temperature if the acid is contaminated with the proper species [2].

Further comments related to the presence of select metals:

Although aluminium has a good resistance to almost all the concentrations of acetic acid at room temperature, care must be taken that the metal is free of other impurities such as iron, copper, tin and lead even in traces [2]. With increasing purity of aluminium, its resistance to acetic acid solution increases, and 99.5% aluminium can be used for the majority of engineering purposes, but components added to its alloy can increase the corrosion of aluminium in acetic acid solution [14]. Since the metal corrosion occurs via electrochemical reactions at the interface between the metal and an electrolyte solution, electrochemical techniques are ideal for the study of corrosion processes.

And importantly, the effect of pH:

It is well known that aluminium resistance is related to the thin and compact layer of naturally formed oxide on aluminium surface, but this oxide layer is stable only in pH range 4-8. Lower or higher pH values caused prominent destroying of protective layer and thus the significant metal dissolution [15].

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    $\begingroup$ The photo depicts a painted aluminum windows sill, not bare aluminum. So, the concern is the resistance of the paint, not that of the aluminum. $\endgroup$
    – joehua
    Jan 16, 2020 at 9:08
  • $\begingroup$ So basically the worse that can happen is it could cause corrosion on the window sill? Would you know if it likely the window sill is aluminium alloy? $\endgroup$
    – Brett
    Jan 16, 2020 at 19:49

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