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New Indian Sandstone patio

Can anyone help me please? What are these marks on my new patio and will they go away? It was laid at the beginning of April 2021.



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You just wash it off with lots of clean water and a mop. You'll need to do this many times - change the water - it will eventually disappear. Living in a country where everything inside and outside is tiled, it's quite a common occurence.
Just hosing it won't get rid of it.
KT53 - the builder who laid the patio has never seen this before either and I do believe him. I can only think that the frosty nights throughout April have something to do with this. I am going to continue to wash and mop and now we have the first rainfall due since March am hoping that will help to reduce how it looks.
Having spent a large part of my life involved in the building trade, I'd been concerned that a builder who hasn't seen efflorescence before probably hasn't laid many bricks or patios 🙄
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
Dovefromabove our builder identified the problem, but mentioned in his experience, had not seen it appear on Indian Sandstone that he has laid in the past. Thanks for the website it is really informative and the mention of it happening more often when daffodils are out struck a chord as we did indeed have daffs in the garden when the patio was laid!
Will post more photos in coming weeks. Just goes to show we can learn something new each day