patchy sandstone slabs

[23vc]

Hi
any idea whats happened here and if its likely to go away?
Slabs laid on solid base wettish 1:6 sharp sand / cement On top of existing concrete.
not sure but hoping it's not similar to what you get when you spot bed and it shows through?
Any ideas welcome!

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• 23vc
• 17 Apr 2015
• 1

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[r896neo]

how long have they been down? the problem with laying over a solid concrete base is hat there is nowhere for water to go but up through the flags leaving efflorsence trails and patchs.

If they have been down a long time it looks like something was spilt on them.

a picture from directly above would be useful as that one is not super clear.

 

[23vc]

Cheers for the reply, I laid them about 4 weeks ago. Looked fine when they went down as you can see in this pic

Untitled

• 23vc
• 17 Apr 2015
• 1

Not sure if anythings got on them. I'll try and get a pic from above of later
There was a strip which I wet concreted on the day before laying which I reckon might line up with most of the patches, was that a big mistake, reckon it'll eventually dry out?
Thanks again

 

[r896neo]

if they are only down that long it could still be efflouresence coming out of the mortar. this is especially common on a solid concrete base as the moisture has to come up.

If it still looks funny after 2 months and drier summer weather it may be something else.

Did you use sbr in your bedding by any chance?

 

[23vc]

Thanks mate. Yes I think and hope you're right. It's changed again now and gone white and strange blotches so that's definitely efflouresence.
no didn't use sbr, used a bit of normal plasticiser, ?