Newly laid patio disappointment

[Evolved]

We have just invested a small fortune into getting our outside space fit for summer which included having a new patio laid.

We chose some lovely 600x600 honed grey sandstone slabs which when they arrived looked superb, the colour was really flat and smooth. The guy we paid to lay them has done lots of fantastic jobs previously and took his time preparing a very solid base with a nice deep bed of MOT and a full bed of mortar to lay them on. He has done a superb job in laying them but we have noticed after a couple of weeks of being down that they're started to darken and go blotchy in areas, which is detracting from the look we wanted.

I've asked the guy that fitted them why and he's not really sure, did a quick search online and not really found any answers, so thought I'd ask here.

Any ideas why they'd do this?

Edited by Evolved on Saturday 21st May 23:16

[MG-FIDO]

Should they have been primed/sealed in some way? Has the cement/adhesive leached into the stone? Hard to say anything without seeing what's happened.

Edited by MG-FIDO on Saturday 21st May 18:11

[INWB]

did he use concrete to set them or use sand? how thick are the slabs?

[HappyMidget]

As above, they probably just need sealing. You can get a large bottle of sealant then just apply with a mop. After a good jetwash first though. I would check with the manufacturers to see what they recommend.

[Evolved]

No they're not seal YET as they've not been pointed and finished yet due to the rain. They've been laid onto a full bed of mortar not a spot bed. The MOT base is around 6" thick and very firm and then it's got around 4" of mortar.

It's raining (again) but I'll try and get some pics once it's dried out to show what's happened. It almost looks as though they're constantly wet in areas but we did have a period where we had sun on them for a couple of days so I know they're not.

[bogie]

Perhaps just the nature of the stone chosen and it needs to dry out ? Are they from a brand name like Bradstone ? if so the stone itself will have a warranty if laid by approved installer

[SAB888]

We always use a sand bed not mortar. Wonder if the slabs aren't drying and it's damp showing through from below.

[Kinkell]

They've been down 4 weeks and not yet pointed. 4" of wet mortar ? This is not a pro job by any industry standards. That said, stone is a natural material and will have its quirks known as character within the trade and will probably be fine.

[Evolved]

Kinkell said:

They've been down 4 weeks and not yet pointed. 4" of wet mortar ? This is not a pro job by any industry standards. That said, stone is a natural material and will have its quirks known as character within the trade and will probably be fine.

Nope didn't say 4 weeks and the pointing is governed by the weather. The job itself was only finished on Thursday but 'some of the flags have been down for around 2 weeks and they've discoloured. Can you explain why 4" of wet mortar is a problem? I'd be more concerned over a thin base but obv looking for advise.

[Evolved]

SAB888 said:

We always use a sand bed not mortar. Wonder if the slabs aren't drying and it's damp showing through from below.

A sand bed for slabs? The block pave he's done is on grit sand and looks great but the patio is on a wet mix of mortar which has now dried obv.

[Evolved]

INWB said:

did he use concrete to set them or use sand? how thick are the slabs?

It was a 4/1 mix of grit and cement for the mortar bed. The slabs are 20mm thick.

[Gingerbread Man]

I believe this is due to voids under the slab. The stone being porous tends to show these areas up. But you say it is laid on a full bed?

To use a link to everyone's favourite paving site - http://www.pavingexpert.com/layflag1.htm

[Kinkell]

Don't quite know why a landscaper would use relatively expensive wet mortar at 4" to achieve a level for laying stone paving but you can ask him. The slabs are now machine cut on the laying side and this means they are less variable in thickness and easier to handle and lay. We used to lay the thickest slab first and use minimum mortar with subsequent slabs brought up to the level with increasing amounts of mortar.
Modern resin pointing can be used in wet conditions once the slabs can be walked on and outlasts traditional pointing.

[dickymint]

Kinkell said:

Modern resin pointing can be used in wet conditions once the slabs can be walked on and outlasts traditional pointing.

In fact it helps if it is raining


https://www.youtube.com/watch?v=T1YwKMeOams

[herewego]

Kinkell said:

Don't quite know why a landscaper would use relatively expensive wet mortar at 4" to achieve a level for laying stone paving but you can ask him. The slabs are now machine cut on the laying side and this means they are less variable in thickness and easier to handle and lay. We used to lay the thickest slab first and use minimum mortar with subsequent slabs brought up to the level with increasing amounts of mortar.
Modern resin pointing can be used in wet conditions once the slabs can be walked on and outlasts traditional pointing.

Could he be trying to compensate for the slabs being only 20mm thick?