Composite decking stains

[Pocster]

Someone lazy in our household left concrete blocks on the decking for some considerable time . On removing them get these white marks . Tried cleaning them with various things but won’t budge .

This permanent or can be removed ?

 

Some people ! Buy materials ; leave them for a bit and then cause more work . I don’t know ! Tsh !

[Onoff]

It was caused by "concrete"? Yeah, right! 😉

[Onoff]

I'd try a bathroom / kitchen limescale remover. 

[crispy_wafer]

bigger plantpot = what stain 🤣

[Conor]

More likely a chemical reaction between the wet concrete and the boards.

[Pocster]

46 minutes ago, Onoff said:

I'd try a bathroom / kitchen limescale remover. 

Tried that.

[Mr Punter]

Brick acid?  Do a test patch first.

[Pocster]

Just now, Mr Punter said:

Brick acid?  Do a test patch first.

yeah I did think of things like that. But is a visible area so its tricky to "test" a patch......

[Onoff]

What about Pink Stuff? 

 

Been surprised at what that shifts, calcium deposits engrained on glass etc.

[Pocster]

3 minutes ago, Onoff said:

What about Pink Stuff? 

 

Been surprised at what that shifts, calcium deposits engrained on glass etc.

Bit rude mate!

[marshian]

49 minutes ago, Pocster said:

yeah I did think of things like that. But is a visible area so its tricky to "test" a patch......

Put another concrete block in a non visible area so you can test it there?

[Pocster]

1 minute ago, marshian said:

Put another concrete block in a non visible area so you can test it there?

😃. yeah I think those marks were left by blocks that might have been there a bit of time....

Like 1 month ..... or 6...... or perhaps it was a yr or 2 🫠

 

BUT! As a long term experiment which therefore stops me fixing it now its a very plausible test!

[marshian]

2 hours ago, Pocster said:

😃. yeah I think those marks were left by blocks that might have been there a bit of time....

Like 1 month ..... or 6...... or perhaps it was a yr or 2 🫠

 

BUT! As a long term experiment which therefore stops me fixing it now its a very plausible test!

Perfect solution - glad I could help

[Russdl]

Not the same materials, however we had a cast iron seat on our porcelain tiles, when I moved it there were little rust marks where it had been stood. Nothing shifted those rust marks, tried everything…

 

…and then I used a Brillo Pad, and that did it. 
 

May work for you?

[crispy_wafer]

gpt reckons vinegar, or citric acid and leave for 10 minutes to try and dissolve the calcium deposits... Might need a few repeats.