Loose paving on steps

Discussion in 'Landscaping and Outdoors' started by mikehatt86, Jun 4, 2020.

  1. mikehatt86

    mikehatt86 New Member

    I laid 8 limestone paving slabs around 2 weeks ago and unfortunately most have already come loose and can be lifted up. The pavers don't wobble when walked on so I believe they are level but they have not adhered to the mortar.

    I laid the pavers on a full bed of mortar using a 6:1 mix of Sharp sand and cement as recommended on a number of websites. I cleaned the pavers thoroughly with water to remove debris and then brushed on a diluted waterproof PVA to the back of the slabs before laying.
    As seen in one of the pics the paving was to sit on a brick wall all around edges and then the middle had been filled with a subbase.

    The paving appeared to have set and everything seemed rock solid for about 2 weeks and then I noticed one of the pavers was loose, checked the rest by trying to lift and about 3 others moved.

    What could have gone wrong? It was a very warm day when they were laid, about 25 degrees and the patio is south facing so was getting a lot of sun when drying out. Could this have affected it?
    I've also read up that maybe I should have used an SBR to help the pavers stick?

    What are my options now? Is there any way to rectify without having to remove the whole mortar bed and start over?

    Paving 1.jpg Paving 2.jpg
  2. mikehatt86

    mikehatt86 New Member

    Guys you've helped in the past, any chance you might be able to offer some advice again? @Abrickie & @chillimonster
  3. Kas228

    Kas228 Screwfix Select

    Hi, you have answered your own question. SBR is the answer, one of its uses is to improve adhesion of mortar to pavers slabs etc. I am laying granite slabs soon and been told that SBR is a must due to low porous nature of the natural stone.
    What type of pavers did you use? Never used SBR before on normal man made slabs.
    SBR is about £17-18 per 5 kg pot and for this sort of use is brushed into underside of slab at ratio of 1:5 with cement some need same amount of water. I created a similar thread recently enquiring about SBR, if you look at my profile it will show in recent postings.
    mikehatt86 likes this.
  4. DIYDave.

    DIYDave. Screwfix Select

    Only diy me but you sound like a desperate man o_O

    SBR for sure should have been used over PVA (even being a waterproof variety)

    Cant see how the slabs will get a great bond anyway as only solid surface for mortar bed to stick to is 100mm of brick depth around the edge
    Vast majority of slab your trying to bond with mortar onto sub base which I guess you've just tipped in and compacted ?

    Slabs on top step at least have brick edge front and back so have a little more chance to bond with the mortar whilst lower step only has that 100mm at front edge

    Admittedly, ive never built steps like these but 'think' I would have taken up most of the depth with sub base/mot/ well compacted then laid a solid bed of mortar at least 75mm to bed slabs onto - and SBR to improve the bond

    You may be able to remove the mortar from both bricks and slabs with hammer and cold chisel, have you tried ? Depends what its actually bonded to, sometimes one material but not the other

    By the way, the brickwork, doors and steps at least all look fantastic, I must say …. as does your dog :)

    Wait for the pros in the meantime
  5. Kas228

    Kas228 Screwfix Select

    mikehatt86 likes this.
  6. DIYDave.

    DIYDave. Screwfix Select

    As you mention, SBR usually available as a 5lt only
    If just a few slabs to lay, Wickes sell a handy 1LT size for just over £4
    By the time its diluted that gives you 5lt anyway so a little pot goes a long way ;)
  7. Kas228

    Kas228 Screwfix Select

    Absolutely made for this job
  8. mikehatt86

    mikehatt86 New Member

    Thanks for the advice @DIYDave. & @Kas228.
    Dexter the dog always enjoying watching what i'm up to!

    As you can probably guess I am just a DIY enthusiast. Pretty pleased with my first attempt at brick laying at least! Just the paving not quite gone to plan.
    So sounds like I definitely should have used SBR to get a proper bond to the paving stones, live and learn.

    This weekend will be spent trying to remove the mortar bedding and re-doing it!
  9. Kas228

    Kas228 Screwfix Select

    Would like to hear how you got on with the SBR so keep us updated. Will be doing my own next week
  10. Abrickie

    Abrickie Screwfix Select

    Whilst you are breaking up the mortar it will save you grief in the future if you take out the infill for the bottom step, run a couple of course to pick the back of the slabs up and backfill again, otherwise you risk the 2 middle slab dropping backward and the end ones twisting. And not all SBR is created equally, read the data sheet before you purchase ;)
    WillyEckerslike likes this.
  11. DIYDave.

    DIYDave. Screwfix Select

    Yes, SBR over PVA for sure but still think you need to change construction method

    You’ve got very little contact between solid surface (100mm brick depth I'm guessing), mortar bed and slab

    100mm front and back top step
    Only 100mm at front on lower step
    Extra 100mm at edge slabs

    Can’t see how a thin-ish mortar bed under slab will bond to loose fill ?

    Try and remove mortar with hammer and bolster and/or score with 4” angle grinder to weaken first

    As I said I’m diy myself but would reduce level of sub base, compact well then lay solid bed over complete area of 75-100mm mortar to fully bed slabs onto

    Not sure if this is correct but think that’s how I would do it - rightly or wrongly !
  12. David Steeley

    David Steeley New Member

    Hi, I laid my own patio a couple of years ago using Stonemarket Dorian limestone slabs. I contacted Stonemarket for latest advice regarding bedding mix and they recommended using 5:1 builders sand and cement as the adhesion is better than if using sharp sand. They also said to use a bonding slurry and I used Instamac Pro. Job went very well and no moving slabs including a step.
  13. Kas228

    Kas228 Screwfix Select

    Some recommend using a mixture of building sand and sharp sand for slab laying.
  14. David Steeley

    David Steeley New Member

    Hi, yes I have also been relaying some Stonemarket Millstone flags as a garden path and as coping to a wall. I used a 3:3:1 sharp/builders and cement for this work and used SBR for the slurry. Just to clarify, I have copied in the advice I received from Stonemarket regarding laying limestone flags.


    Thank you for your enquiry. Our recommendation would be that the mortar be made up of 1 part cement to 5 parts building sand.

    We have found that we get a better adhesion using the building sand as opposed to the sharp sand

    With regards to the slurry primer we would recommend the use of a slurry primer, the one we are able to offer is Instarmac Pro Primer slurry. Each bag of this would cover approx. 15m2 when mixed to the manufacturers guidelines.

    I hope that this answers your questions but please contact us if you need any further help.
  15. DIYDave.

    DIYDave. Screwfix Select

    I think apart from the lack of SBR to improve bond, it’s also the construction that’s not helping

    Contact area between brick, mortar and slab is only brick width (100mm ?) front and back at top step, lower step, just 100mm at the front

    How does mortar bond to loose sub base that is covering what, 80% of the slab ?
  16. Kas228

    Kas228 Screwfix Select

    Aren’t most patios/paths etc laid direct on to loose albeit compacted sub base?
    Abrickie likes this.
  17. Jord86

    Jord86 Screwfix Select

    I believe you answered your own queries in your first post by stating you used PVA on the slabs rather than SBR, bedding them on a very hot day, at a guess you didn't dampen the bricks/sub-base before laying and looking at the first picture the infill scalpings are quite uneven with a large bump in the middle of the rise, if you laid mortar directly on that then it wanted to be a pretty large bed especially on the right hand side in order to bring the slabs up to level. If the sub-base was tamped down compact and level, the area dampened first to aid adhesion and a good full bed of compo was used I think it would have stayed put. Try a 4 to 1 mix, being a step with possible high traffic area.

    Nice first attempt though,better than some trades I've seen.
    WillyEckerslike and Abrickie like this.
  18. Abrickie

    Abrickie Screwfix Select

    Er being as the slabs have parted from the mortar but the mortar has got to be chopped off the base, don’t really think the base is an issue is it:rolleyes:
    Jord86 likes this.
  19. Jord86

    Jord86 Screwfix Select

    Depends if you're in a wheelchair or not :cool:

    Abrickie likes this.
  20. Abrickie

    Abrickie Screwfix Select

    His mother in law is hence the steps :D
    Jord86 likes this.

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