Spots on limestone patio slabs

[JRSmith138]

A few months ago we had a new limestone patio layed by a local company.

I have noticed the after rain there are circular marks left on some of the slabs.

I have queried this and been advised it's the salt in the slabs which can take a few months to come out.

They have said if it doesn't dissappear by Feb they'll come back and take a look.

Does this sound right? I'm concerned it may be caused by some of the slabs only being spotted underneath (you can see above however it isn't on all of them), or perhaps an issue with the Sealant.

I also note that the same thing occurs following recent snowfall.

Any advice would be much appreciated!

 

[yorksbuilder]

Yes it's a giveaway that they didn't use a full bed of mortar under each slab, but rather had a spot bedding approach which results in the damp patches and picture framing effect. Did you see them in action? See this link for more info: https://www.pavingexpert.com/layflag1

 

[motorbiking]

As above, it's the contact with the mortar bed showing through. A give away that they haven't been laid properly.

 

[noseall]

A few months ago we had a new limestone patio layed by a local company.

I have noticed the after rain there are circular marks left on some of the slabs.

View attachment 368010
I have queried this and been advised it's the salt in the slabs which can take a few months to come out.

They have said if it doesn't dissappear by Feb they'll come back and take a look.

Does this sound right? I'm concerned it may be caused by some of the slabs only being spotted underneath (you can see above however it isn't on all of them), or perhaps an issue with the Sealant.

I also note that the same thing occurs following recent snowfall.

View attachment 368011

Any advice would be much appreciated!

Limestone slabs do effloresce unfortunately and is usually harmless.

 

[Cheslea2010]

This is not showing a full mortar bed...yeehaw!

 

[Nwgs2]

A few months ago we had a new limestone patio layed by a local company.

I have noticed the after rain there are circular marks left on some of the slabs.

View attachment 368010
I have queried this and been advised it's the salt in the slabs which can take a few months to come out.

They have said if it doesn't dissappear by Feb they'll come back and take a look.

Does this sound right? I'm concerned it may be caused by some of the slabs only being spotted underneath (you can see above however it isn't on all of them), or perhaps an issue with the Sealant.

I also note that the same thing occurs following recent snowfall.

View attachment 368011

Any advice would be much appreciated!

Have they sealed the flags ?

 

[JRSmith138]

Thanks all for the responses on this, I'll be getting back in contact with the company as during initial discussions they had said they'd use a full bed (unfortunately no did not witness this in person).

To answer the second point, yes it has been sealed.

Assuming only way to resolve this is to have the bed completely re-done?

 

[noseall]

Assuming only way to resolve this is to have the bed completely re-done?

No. It can still effloresce.

 

[Ivor Windybottom]

No. It can still effloresce.

...but evenly or randomly, not in the telltale pattern shown here.

The snow photo is brilliant, almost like an x-ray as there's more retained heat where it's solid. There's fresh air underneath everywhere the snow remains.

It looks like they've put a bed around the edge and a blob in the middle of each. So they are more likely to sink or crack but there are no guarantees either way. It looks like they must be pretty thin slabs for it to be this apparent, more like tiles than slabs.

This is the sort of reason why I DIY almost everything.