Patio slabs

Discussion in 'Builders' Talk' started by CaraDavies, Sep 6, 2021.

  1. CaraDavies

    CaraDavies New Member

    I’m living on my own and I have recently had patio slabs laid by a builder. There is quite a large surface area laid and I have counted 21 slabs that can be lifted after being laid. Builder flattened the ground with a Wacker plate and laid slabs on a wet mix. The slabs are not rocking but are loose and can be lifted. He has started jointing the slabs but I have asked him of his plans for fixing the loose slabs and he said that he is using glue. He hasn’t used a SBR adhesive. Am I right in asking him to lift the old mortar bed out and relay or will an adhesive work. I checked the one he said he has glued and it can still be lifted. I’m just worried with the amount of slabs that haven’t been laid securely to the mortar bed. Thankfully I haven’t paid the builder. Any advice appreciated as I am a female and want to make sure I have all facts before speaking to him.
  2. Truckcab79

    Truckcab79 Screwfix Select

    The acceptable number of slabs that should be able to be lifted is zero. The pointing will stabilise it long enough for you to pay him and then the movement will break it all up.

    The ‘glue’ he is using if anything is probably a slurry of SBR and cement. Surprised it hasn’t worked to be fair though its not the right way to do it. The fact that it hasn’t stuck would suggest to me that he hasn’t even done that. Are you sure they are on mortar and not just on a sand bed?
    CaraDavies likes this.
  3. CaraDavies

    CaraDavies New Member

    I don’t think he has used the glue (what ever this might be) on the slab as it’s still lifting despite adding Sika compound to joint. He has used Portland limestone cement, sand and stone for the mortar base. Do you think it’s reasonable to ask him to try and use adhesive or to lift old mortar bed and start again?
  4. Truckcab79

    Truckcab79 Screwfix Select

    I’d stop him now and he needs to either start again or walk away without payment. That’s a very difficult conversation to have I appreciate.

    There is no ‘glue’ that sticks slabs back down if they’re not laid properly. They stick to the mortar bed. Do you have pictures of the mortar bed or any pictures of the project during construction?
  5. CaraDavies

    CaraDavies New Member

    I know I was thinking along the same lines. I haven’t taken any photos during construction but I can lift three or four slabs next to each other as they are loose and take pictures of the mortar bed.
  6. Truckcab79

    Truckcab79 Screwfix Select

    Great. Pictures of the slabs he’s trying to lay and pictures of the underside /back of them as well. Thickness of mortar bed if it’s possible to see. You should be looking to find 30-40mm as a minimum and by now I would expect it to be rock hard so might be difficult to determine the thickness.
    Last edited: Sep 6, 2021
    CaraDavies likes this.
  7. CaraDavies

    CaraDavies New Member

  8. CaraDavies

    CaraDavies New Member

    Measured and the mortar base is 20 mm. Tried uploading photo but file too large.
  9. Truckcab79

    Truckcab79 Screwfix Select

    Too thin really. Doesn’t mean it won’t stick but is reflective of the quality of work.

    Theres probably an app that will reduce the res of the photos. Bit long-winded but on the odd occasions when I need to, I email them to myself and certainly on iPhone it allows me to reduce the quality. I then send at ‘medium’ and copy and paste.

    Should have asked earlier but are the slabs lifting with the mortar attached or are they lifting off clean?
    CaraDavies likes this.
  10. koolpc

    koolpc Super Member

    Dont pay him anything. Tell him you want it all dont properly. Make sure you have a witness or someone who can back you up with you..
    CaraDavies likes this.
  11. DIYDave.

    DIYDave. Screwfix Select

    What are the slabs made of ? Cement / Stone / Porcelain ?

    If cement/stone / these are porous and have sucked the water out the mortar bed, not helped by also being dry and dusty

    If porcelain, the opposite, they’re not porous so the mortar finds it hard to get a grip onto the material

    At least dampening down the slabs if cement/stone will aid adhesion, if porcelain, absolute must to use SBR Priming Slurry on the backs

    Pointing the slabs will hold them firm for a while but that’s relying on a small surface area of the slab only, instead of 100% adhesion from the underside - as well as pointing

    Good advice from Kools above - be prepared for a ‘fight’ and have some backup for yourself - good luck
    CaraDavies and koolpc like this.
  12. Severntrent

    Severntrent Screwfix Select

    If they are not rocking about whats the issue. I laid my patio as well as various garden paths on a grit sand bed and they are still in position. If I wanted to I could lift anyone of them but why would I want to go round doing that.
  13. Offshore

    Offshore Active Member

    I have to admit, I was thinking the same. Not wishing to dismiss the OP's concerns in any way, but I thought it was normal practice to lay slabs on a relatively dry mix with further dry mix dusted in to the cracks and let everything go off over time rather than fix them with mortar in the first instance. The only exception to this, in my own experience, was my driveway where two sets of runners were laid on top of concrete as opposed to mortar, this was to support the weight of a car though, so slightly different to a patio I imagine.
  14. Truckcab79

    Truckcab79 Screwfix Select

    I lay most on a fairly dry mix, with SBR primer regardless of stone type. Regardless they are all firmly bonded the following morning. You won’t be lifting any of them up. If you have a completely uniform slab to lay and it’s for light traffic then by all means lay it on a bed of compacted sharp sand. No mortar required at all.

    Pointing should never be just brushed in. It’s a bodge and if you try a comparison between brushing in until ‘full’ and how much you can get in to a joint before its full if you compact it down until there is no give, then you can see why.

    Ill not comment further unless there are some pictures and it would be good to know what spec if any the client received. If it’s a cheap job then maybe it’s fine.
    koolpc likes this.
  15. CaraDavies

    CaraDavies New Member

    F1820F0E-8796-4D19-9C2A-A5061EDE65F7.jpeg F811FA05-3C6E-4352-B6AF-8B539A2A5D6C.jpeg 7C42F859-E75A-4359-8550-7057575D9F12.jpeg 9C020E9D-1DFB-4F46-8C93-1E985B57229E.jpeg

    Managed to upload. They are a Sandstone tile. Have a look but grateful for your advice?

    Attached Files:

  16. Truckcab79

    Truckcab79 Screwfix Select

    Needs to be done again. There is no adhesion between stone and mortar bed at all. Difficult to say why without seeing him mix the mortar and lay it. You can see from the shape of the bed that it was put down reasonably wet (well, not dry at least). There is no SBR slurry on the back and many people have laid sandstone without it but it’s belt and braces and is daft not to as you’re pretty much guaranteed a good bond with it.

    Mortar isn’t a full bed, which it should be. It’s better than the 5 dabs you often see but I’ve seen worse also. Not a reason it shouldn’t have stuck.

    Your call. If you’re happy that it’s stable and you can agree a very much reduced price then let him point it and walk away. If he’s any good he shouldn’t want it left that way and shouldn’t be making excuses for it. It’s happened, suck it up, learn from it, and do it again would be my approach.
    Last edited: Sep 7, 2021
  17. Truckcab79

    Truckcab79 Screwfix Select

    Just looked at photos again. Don’t know what’s going on with that mortar bed. It looks like the base layer isn’t well compacted? But very difficult to see from one photo. It also looks like the mortar also contains the base stones, which to be fair is how you described it earlier but I assumed that you meant the stones were in the base. This looks like your mortar bed is sand, cement and stones????
  18. DIYDave.

    DIYDave. Screwfix Select

    Picture 2 - if that’s the underside of the slabs, then there’s zero adhesion to the mortar as the slabs are crystal clean

    Picture 4 - slabs should be laid on a full bed, not just square frames of mortar

    The only function the mortar has served here is to level the slabs, there’s no bond and slabs aren’t fully supported

    Ok, might just be foot traffic and not a driveway or expecting a herd of elephants but it don’t make it right in this method

    Have a look at this great site that covers everything to do with groundworks and paving, it’s well respected and factual and a goldmine of quality information. Worth doing some research on ‘best practice’

    The Paving Expert
    CaraDavies likes this.
  19. CaraDavies

    CaraDavies New Member

    Thanks all for your advice. It is really helpful to get some expert advice. Have a great evening all. I will check out the website you refer to ‘The Paving Expert’.

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