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Refixing loose patio slab

Discussion in 'Home and Garden' started by Merlin5, 4 Aug 2020.

  1. Merlin5

    Capodecina

    Joined: 17 Aug 2009

    Posts: 16,586

    Location: Finchley Central, London

    I've lifted a patio slab that was rocking when stepped on and also had some broken pointing.

    [​IMG]
    There's loose sand underneath which I've piled to one side and it was covering a bit of a cavity. I'm wondering whether to pat the sand back down and just put some large blobs of sand and cement mix in each corner?


    [​IMG]


    Do I need sharp sand, building sand, or some other type of sand, and would you recommend mixing 4 parts sand to 1 part cement? That's what I've been seeing on YouTube videos. And 3 to 1 for mortar joints? I also want to fill a small hole in my front wall.next to the window frame.
    [​IMG]

    How much sand and cement do you think I should buy? I'm going to go to builders depot they're normally pretty inexpensive.

    I'll need a bucket. And I'll need a trowel but I don't know what size. And should I use a piece of old hose to smooth out new pointing or just fill the gaps around the slab and brush away excess?
     
    Last edited: 4 Aug 2020
  2. sadat

    Gangster

    Joined: 11 May 2020

    Posts: 257

    tbh I don't know about the exact measurement but I will advise you to be careful when working near wet cement and not to get it on yourself or clothes as you can get pretty bad burns.
     
  3. Merlin5

    Capodecina

    Joined: 17 Aug 2009

    Posts: 16,586

    Location: Finchley Central, London

    Burns? Didn't know that.
     
  4. sadat

    Gangster

    Joined: 11 May 2020

    Posts: 257

  5. apg

    Gangster

    Joined: 4 Dec 2013

    Posts: 146

    For underneath the slab mix 4 parts sharp sand to 1 part cement. Compact all of that sand so its nice and flat. Spread the cement mix all over the area where the slab is going to go and as deep as possible. Dont just put blobs in corner. With whats left over you could then poke that into your hole.
     
  6. Merlin5

    Capodecina

    Joined: 17 Aug 2009

    Posts: 16,586

    Location: Finchley Central, London

    Blimey sadat, that's a bit scary. Will marigold washing up gloves do?

    Thanks apg. Good idea to use what's left over for the hole. So, cover over the sandy area too. Not sure what you mean by as deep as possible unless you mean pack the cavity covered by the sand?

    Do you think these will be enough for under the slab, the pointing and the hole in the wall? It doesn't say how many Kg in the sand bag.

    https://www.diy.com/departments/tarmac-sharp-sand-large-bag/5030349012445_BQ.prd

    https://www.diy.com/departments/blue-circle-multipurpose-cement-25kg-bag/35715_BQ.prd?rrec=true
     
  7. apg

    Gangster

    Joined: 4 Dec 2013

    Posts: 146

    I mean when you lay the cement mixture make sure its not just 1mm thin. Try and put a good amount down so the slab can bed in properly.

    Yes a sinngle bag of sharp sand and a single bag of cement will be more than enough.
     
  8. wedrum

    Soldato

    Joined: 11 Aug 2016

    Posts: 5,536

    Location: Cheshire

    Gorilla glue be reet
     
  9. Merlin5

    Capodecina

    Joined: 17 Aug 2009

    Posts: 16,586

    Location: Finchley Central, London

    Awesome, thanks, I'll get those tomorrow.
    I'm also going to buy a 26 litre gorilla tub, it's one of those very flexible mixing buckets that should make it easier to clean away dried cement.
    A gauging trowel and maybe a tuck pointer unless I can find something at home to bed the pointing mortar in place.
     
  10. sadat

    Gangster

    Joined: 11 May 2020

    Posts: 257

    Lol. Definitely.
     
  11. sadat

    Gangster

    Joined: 11 May 2020

    Posts: 257

  12. Merlin5

    Capodecina

    Joined: 17 Aug 2009

    Posts: 16,586

    Location: Finchley Central, London

    Thanks, I'll use my old marigolds. Saw a video where a guy was handling a sand and cement wet mix, although a fairly dry wet mix, with thin nitrile type gloves.
     
  13. sadat

    Gangster

    Joined: 11 May 2020

    Posts: 257

    Yeah nitrile gloves should be fine as well.
     
  14. joelk2

    Soldato

    Joined: 22 Nov 2010

    Posts: 5,490

    I used gloves with no fingers and did my whole patio with cement and didnt get any burns. Constantly had cement on my hands.
     
  15. Zefan

    Don

    Joined: 15 Jan 2006

    Posts: 31,058

    Location: Tosche Station

    Yeah I too have pretty much bathed in the stuff, no problem.
     
  16. sadat

    Gangster

    Joined: 11 May 2020

    Posts: 257

    Yeah I didn't know about this until recently when we did have an incident and then got briefed about it.
     
  17. sadat

    Gangster

    Joined: 11 May 2020

    Posts: 257

    I think it's when you have sensitive skin so you get the burns from a chemical reaction. Here's an extract:
    "Cement can cause caustic injury, resulting in chemical burns of any part of the body it comes in contact with - skin and eyes, mouth and throat if swallowed, and lungs if cement powder is inhaled. Cement is largely made up of calcium oxide. When it reacts with water, it produces highly alkaline (high pH) calcium hydroxide that can reach a pH of 12 or higher within a couple of minutes. This is why dry cement is less caustic than wet cement. Remember that the pH tells us how acidic or alkaline a solution is on a scale of 0 (most acidic) to 14 (most alkaline), with a neutral pH being about 7. So, because the pH of wet cement is so high, it can cause burns."
     
  18. bainbridge

    Mobster

    Joined: 9 Dec 2009

    Posts: 4,231

    Location: Bristol

    Yes cement is caustic when mixed. Some people don't seem to be affected and others are more sensitive. Some people are fine handling it with bare hands for years and then suddenly become sensitive to it.

    I'd glove up to be safe, also I'd refrain from having a sneaky poo in the garden and using a bit of cement bag as loo roll.
     
  19. ChroniC

    Sgarrista

    Joined: 18 Oct 2002

    Posts: 9,466

    Op... Dig out about half and inch of all the old sand and remove any cement from the edges of the other tiles.

    Get one bag cement and one bag builders/sharp sand (no gravel in it) Make up a mix of 1 part cement to 3-4 parts cement. No water...

    Put the new mix down level and flat. (piling in corners creates a vacuum under the slab and will crack it) place the tile on sand and using a small level to make it accurate.

    Using a slightly strong 50/50 mix of sand and cement and pack it into the gaps evenly around the edges.

    You can leave it after that, the moisture in the air with eventually set it in place. However the packing of the sand should make it very strong in place anyway.
     
  20. Merlin5

    Capodecina

    Joined: 17 Aug 2009

    Posts: 16,586

    Location: Finchley Central, London

    So mix one part cement to four parts sand and no water. Then mix 50/50 sand and cement for the pointing, I presume I must add water to that though?
     
    Last edited: 5 Aug 2020