Advice on indian stone patio

Hello,

We have recently had a gazebo fitted with an indian stone patio for the floor. Today we noticed something weird - there is a wet, regular pattern on some of the stones, but they are in part of the gazebo that doesn't get wet. I'm worried that the wet is coming up from the ground and something is not right with how the builder laid them. (I'm not convinced they are of the best quality either). I have attached a photo, so hopefully someone can put my mind at rest or tell me what's wrong.


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Posts

  • B3B3 Posts: 6,375
    It looks like where cement was dolloped before the slabs were laid.

    In London. Keen but lazy.
  • Lizzie27Lizzie27 Bath, SomersetPosts: 1,054
    I would expect that they will dry out soon, have you had a lot rain since they were laid?
  • LantanaLantana Posts: 4,633
    If you mean the grey middle stone in the photo with the circular marks then I’d agree with B3. That was the first thing that came to my mind too, dollops where it was laid. Hopefully it’s all still drying out and despite that area having been under cover there will be residual dampness.
  • plant pauperplant pauper Posts: 5,907
    If it doesn't have a DPC membrane, the dollops of adhesive will be wicking damp up from the ground surely...? No?
  • WaysideWayside Posts: 602
    People like to dollop mortar, but I'd have thought you'd need to lay these on a bed, as usually this type of sandstone is quite thin.  It's a bit of an odd pattern, you'd expect corners and middle if they were dollops.
  • craigwrightcraigwright Posts: 7
    Thanks everyone. Yes, I thought it might be cement, so that could be it. But is it a problem? Will it go away over time? 

    They used some cement mixed with something else to aid drying. I don't know much else about it.

    We have had a lot of rain in the past few days, but this has to be coming from underneath, because this area of the patio is completely dry otherwise. The marks weren't there before it rained and I'm just a bit worried that something's not right underneath.
  • NollieNollie Girona, Catalunya, Northen SpainPosts: 599
    It looks like your builder has used an inappropriate but all too common technique - spot adhesion or dolloping should never be used with any natural stone - you need a full wet mortar bed application. I always use flexible adhesive and back-butter the slabs because it creates a good bond and a cushioned surface to absorb the knocks and footfall.

    Dolloping creates an unstable base for what is often a fragile material. Quality, calibration and grading of Indian SS varies enormously and tbh yours doesn’t look like it’s top grade - I can see areas that are likely to flake off or ‘delaminate’ which is common in the seconds and even lower seconds reject grades.

    Dolloping also creates voids for moisture to collect and the dollops not only wick up moisture, but fine cement particulates and are likely to permanently stain - no amount of scrubbing (don’t use acid cleaner whatever your do!) will remove them if this happens as they are right through the stone.

  • FireFire LondonPosts: 4,125
    edited 13 August
    @Nollie - now here is someone who knows her paving techniques.
  • plant pauperplant pauper Posts: 5,907
    Yip!
    What @Nollie said. 
  • craigwrightcraigwright Posts: 7
    So what should I do about it? I'm getting the feeling that the whole lot needs to come up and be replaced - the builder supplied the stones, so it wasn't like we chose them. 
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