Hole in concrete floor

Discussion in 'Getting Started FAQ' started by Si Notaclue, Nov 7, 2017.

  1. Si Notaclue

    Si Notaclue New Member

    Evening all, thanks for reading this.

    Just to be clear, I'm an absolute amateur at DIY, but have bought a flat and it needs a lot of work.

    It's a 40s/50s ex-council block, lots of redbrick and cement etc. There was a raised section in the hallway floor, approx 15mm high by 250mm wide, running diagonally across. Similar situation in the bedroom the two follow the same line, I'm assuming they're connected.

    First thought was to use self leveling compound to raise and level the two floors but a mate advised against, and suggested I chisel out the raised area and back fill/level the hole. So I bought a cold chisel and set to work...

    I found the floor was in several layers. On top, a dark red cement type material (~15mm), underneath that a cement coloured cement type material (~5-15mm, but this was only in places), and below it all, concrete. The middle layer was all broken and dusty in large part.

    Worryingly, I also found an old pipe that must be causing these problems. The pipe looked very old and corroded (had small holes rusted in it), and the building hasn't exploded yet.

    I'm now left with a sizable hole in my hallway floor. Perhaps 60mm deep at its deepest. Approx 750x300mm at surface.

    Was thinking to fill with some kind of cement at the bottom, leave to cure, then self leveling for the top 5 - 10mm. Carpet or, if it's level enough, laminate will be going on top eventually.

    Does this sound reasonable? Anything obviously wrong with the plan?

    Thanks in advance for any advice.
  2. CGN

    CGN Well-Known Member

    Mix some sharp sand or ballast, 5 parts to 1 cement and Chuck it in. Get a trowel or bit of wood to tamp and 'trowel' level with existing floor.
  3. Si Notaclue

    Si Notaclue New Member

    Thanks for replying so quick CGN.

    So - sorry to be a bit dense - mix up some ready mix cement as per instructions on the bag, then add 5x as much sharp sand, and use that to fill the hole? Level off with a trowel? Sounds straight forward!
  4. CGN

    CGN Well-Known Member

    Buy either a bag of sharp sand or a bag of ballast and a bag of cement

    Sharp sand is a coarse sand, ballast is sand mixed with gravel.

    A small garden trowel or spade if you have one is ideal, so all you do is put 5 trowels of sharp sand, or ballast in a bucket, with one trowel of cement. That's the basic ratio, and you'll have to judge quantity's,by how big the hole is. It doesn't have to be really precise like a cake recipe :)

    Mix it together dry, then add water a bit a bit at a time til it binds together, not too wet, not too dry. Brush the hole with some water then put your mix in.
    Tamp it in till full, and the 'fat' will rise to the top and you'll get a smooth finish which you can trowel and blend in to existing.
    KIAB likes this.
  5. WillyEckerslike

    WillyEckerslike Well-Known Member

    CGN has described exactly what is needed however I just want to correct a misconception you have. Cement is only one of the components of the mix and is added to the sand to make mortar or to ballast (sand and gravel) to make concrete. It's a very easy mistake to make not helped by products called 'ready mix cement' which in reality aren't. You can buy all manner of ready mixed products which will or won't do what you need (just add water, or not in some cases) and they will contain cement. You would not need to add anything else. CGN merely gave you the recipe most appropriate to your requirements if you wanted to buy and mix the ingredients separately.

    It's a bit like calling a bag of bread mix ready mixed yeast. I hope that makes sense?
    CGN likes this.
  6. Isitreally

    Isitreally Well-Known Member

    This video gives you the basic idea, but you need Sharp sand and a 5.1 ratio mix.

    CGN, KIAB and WillyEckerslike like this.
  7. KIAB

    KIAB Well-Known Member

    You will find a lot of this disused old electrical steel conduit buried in the floors of a lot of council houses,it starts rusting out,then causes concrete spalling, which gives you the pronounced cracks & raised ridge running across the floor.

    Have remove lots of it over the years in many council houses, ruins carpets, laminate flooring,only option is to remove it.

    Sharp sand is the best thing to use, ballast contains too much large aggregate, & make sure you well dampen the channel before filling, some old concrete soaks up water like a sponge.
    Last edited: Nov 8, 2017
    CGN and WillyEckerslike like this.
  8. Si Notaclue

    Si Notaclue New Member

    Thanks very much for the advice everybody, it's all really helpful. This is the first bit of proper DIY I've taken on and it's really helpful to have access to so much knowledge and experience. You'll probably be hearing much more from me as I continue to try and get this flat sorted out.
    KIAB and CGN like this.
  9. WillyEckerslike

    WillyEckerslike Well-Known Member

    Thank you for the feedback. The number of occasions that forum members give up their time to help someone with a particular issue only to never hear from them again or learn if the problem was resolved is quite disappointing. Good luck with the flat.
    KIAB and CGN like this.
  10. Si Notaclue

    Si Notaclue New Member

    Update: potentially big problem!

    I'm continuing to chisel out the uneven flooring in the bedroom now (finished excavating the hallway, but not filled it yet), but as I'm approaching the wall the concrete is coming up damp. It feels/smells damp. Also, when I pulled the old carpets up a couple of weeks ago I saw that the underlay was discoloured with water damage in that section of the bedroom. Didn't think much of it at the time, being naive. It's not the whole bedroom, just within about 1000/1500mm of the wall.

    I'm currently having a mild panic that this is going to be horrendously expensive to sort out. I can post photos of everything tomorrow, forgot to take my phone there this afternoon. Hopefully there's something I can do myself, rather than paying a builder to come in.

    I'll be very grateful if anybody has any initial thoughts/further questions.

  11. KIAB

    KIAB Well-Known Member

    Photo's will give us a clearer picture.
  12. CGN

    CGN Well-Known Member

    Never panic...its all fixable. People here will help you :)
    WillyEckerslike and KIAB like this.
  13. Si Notaclue

    Si Notaclue New Member

    Sorry for the delay getting these photos up. Here they are: I’ve included a couple of the carpet underlay. I think the carpet was there for probably upwards of 20 years, at a guess.

    Attached Files:

    KIAB likes this.
  14. Si Notaclue

    Si Notaclue New Member

    This is the underlay

    Attached Files:

  15. KIAB

    KIAB Well-Known Member

    I think that water stain is from a previous incident,water being spilt & carpet not being lifted to allow area to dry out.
  16. 2shortplanks

    2shortplanks Member

    Looking at those photos, it looks like the floor has had a channel cut in it and pipes laid in concrete/screed, judging by the way the concrete is cracking out at the end - CH pipes maybe?

Share This Page