Best waterproof self leveling screed for 0mm to 5mm concrete base?

Discussion in 'Builders' Talk' started by rogerk101, Dec 1, 2019 at 10:06 PM.

  1. rogerk101

    rogerk101 Well-Known Member

    I'm looking for opinions on the best self leveling screed to use on my slightly wonky concrete garage floor.
    • It should be waterproof to prevent any rising damp getting through
    • It should accommodate 0mm to 5mm (or thereabouts)
    • It will cover an area of 26m2 (4m x 6.5m)
    • It will have 50mm insulation boards on top of it, followed by 18mm/22mm chipboard, followed by tiles
    • No underfloor heating
    • It should provide me with as much working time as possible (I've never done an SLC before, so definitely don't want rapid set)
    I plan to mix it in regular black building buckets using a slurry mixer on my drill, to spread it with a rake or a sponge squeegy, and then to roll it with a spiked roller.

    All guidance welcome. Kiab, that means you! :D
     
  2. KIAB

    KIAB Well-Known Member

    No leveling compound is a dpm.

    How/what you securing chipboard to?

    Would have looked at a suspended floor, then you could use a liquid dpm on floor.
     
  3. rogerk101

    rogerk101 Well-Known Member

    Thanks for responding, Kiab.
    My biggest problem is that I only have 80mm to play with, and I'd like to max out on insulation, e.g 2mm SLC + 50mm insulation + 18mm chipboard + 10mm tiles = 80mm
    I'm fairly sure I addressed whatever damp there was in the floor when I dug out all round the building and installed a really good damp proof and drainage system ... it's been bone dry inside since then ... but I figured there's no harm in a liquid DPM as belts and braces. (I only like doing jobs once!)
    I was hoping that I could use the liquid DPM as an SLC, or to find and SLC that blocked damp. I don't mind doing both as long as it doesn't raise the floor by much more than 2mm higher than the current highest point.

    I was planning on 'floating' the chipboard, i.e. gluing all the T&G boards together with Gorilla glue and having it just sit on the insulation. I'm sure the Goriall glue will expand out and stick the boards to the insulation, which is OK as long as I leave a decent 5mm gap all round the whole surface so the floor doesn't buckle.
    Adding a ton of tiles to the whole lot should keep it flat, and then once furniture is moved in I can't see much movement happening.

    With only 80mm to play with? I guess I could use roof tiling battens (25 x 38) screwed into the concrete base, but that would create new holes in the floor, and risk making damp proofing even more of a challenge.
     
  4. LEH

    LEH Active Member

    Tiling onto a floating chipboard floor is asking for trouble I’m afraid.
     
    KIAB likes this.
  5. KIAB

    KIAB Well-Known Member

    Agree.
     
  6. rogerk101

    rogerk101 Well-Known Member

    I'm trying to get the best insulation possible, so what method/system does the panel suggest?
    The only 'fixtures' I have at the moment are:
    • a level, but slightly wonky concrete slab
    • the floor tiles, which I had left over from another project
    • 80mm maximum height gain
     
  7. rogerk101

    rogerk101 Well-Known Member

    How about this for a proposal?
    • Liquid DPM to damp proof the whole area
    • Rows of 3x2 CLS timber (actual size around 65 x 45) spaced to accommodate 600mm wide 50mm insulation panels between them, and screwed into the concrete subfloor, but with plenty of silicone in each screw fixing to retain the damp proofing
    • 50mm insulation panels between the 3x2s
    • 18mm T&G chipboard flooring glued together and glued and screwed into the 3x2s
    • Tiles with flexible adhesive and flexible grout
     
  8. KIAB

    KIAB Well-Known Member

    Another way,could screw bearers to walls, then fix joists to that rather than fixing them to floor.

    But,as there should around 100mm of concrete before you get to the dpm,so your method for fixing bearers to floor would be ok.
     
    Last edited: Dec 2, 2019 at 9:54 AM
  9. furious_customer

    furious_customer Active Member

    I am guessing that the 80mm restriction is for a doorway?
     
  10. rogerk101

    rogerk101 Well-Known Member

    The span is 4m, so I'd need many intermediary supports off the concrete base if the maximum depth of the 'joists' is to be 80mm minus the 18mm chipboard and the 10mm for tiles.
    Thinking about it, I could stick the 3x2s to the concrete base with some building adhesive rather than screwing them into it. They'll not move much because they'll be held in place by the many screws and the glue that will be fixing the chipboard to the 3x2s.

    Yes, in fact it's more than just a regular doorway, it's a huge trifold door doorway almost the full width of the building. If it were just a standard doorway, I'd probably just make a small recess in front of it. With such a wide doorway, the recess would have to be pretty much the full width of the room.
     
  11. LEH

    LEH Active Member

    Could look into the 22mm no more ply, that’s a structural product that can be tiled directly onto.
     
  12. rogerk101

    rogerk101 Well-Known Member

    Thanks for the suggestion.
    My floor is 26 square metres.
    I was not familiar with NoMorePly, so I did a quick Google search, which suggested it would cost over £900 if I were to use the 22mm thick 2400mm x 500mm boards! If I shopped around I could probably get that down to £800.
    22mm waterproof chipboard costs £8 per sheet of 2400mm x 600mm, which works out at £144. (With good support provided by the joists plus rigid insulation, 18mm chipboard would probably be fine, and it's even cheaper.)
    I've tiled directly onto 22mm waterproof chipboard in 5 bathrooms and 1 kitchen and all are still good many years on.
     
  13. LEH

    LEH Active Member

    It is ridiculously expensive. Getting rid of the floating setup will at least be better.
     
  14. rogerk101

    rogerk101 Well-Known Member

    Can you help me understand why?
    If all of the boards of waterproof chipboard are glued together with a good dollop of Gorilla glue in the T&Gs, and all of the tiles are glued to the chipboard using flexible tile adhesive and grouted with flexible grout, in what way would that be different from if the chipboard boards were glued and screwed into joists?
    I'm certainly now leaning towards the joists/battens glued and screwed into the concrete subfloor and the chipboard glued and screwed into the joists/battens, but I'm still curious about why you and Kiab both think that tiling onto a floating floor would be such a bad idea.
     
  15. LEH

    LEH Active Member

    Floating floors - too much deflection, even for a 'flexible' adhesive.
     
    rogerk101 likes this.
  16. rogerk101

    rogerk101 Well-Known Member

    Ok. Thanks for clarifying your concern. I too had that concern, which is why I was planning to use a good self leveling screed to reduce the amount unevenness which in turn should reduce the amount of deflection. However, I guess even the best laid SLC is not going to be perfectly flat, and even if it is really close to being flat, the insulation probably won't be uniformly thick and the chipboard as a floater might buckle/warp slightly, etc. etc.
    I'm now completely convinced that the battens fixed firmly to the concrete and the chipboard fixed firmly to the battens is the right way to go. Even if it's not completely flat, at least it's not going to move much more than that the flexible adhesive can cope with.
    Huge thanks for the advice, LEH and KIAB ... really helpful ... between the two of you, you've probably saved me many a grey hair down the line. Mind you, if it doesn't work out, at least I have you two to blame!
     
  17. Multiskillmaster

    Multiskillmaster New Member

    Self level the floor with any old water based diy merchant stuff...then either shallow joists...at 300 centres, insulate between...use a laser to pack all joists with window packers as required (fix down to remove any crowning)... sticks like **** to stick packers to floor and joists to stop them vibrating loose...p5 glued and screwed 15mm WBP, no self level required if you did joists right!... or floating floor on rigid floor grade celotex (what depth you need)22mm P5 sheets, pva all joints...tile regs suggest 15 mm WBP ply screwed to p5 at 100-150 centres.Bostik primer the floor and then bostik self levelling with fibre reinforcement..check floor is flat with laser...this should ensure you get a even bed of flexible tile adhesive with a notched trowel. Flexible mapei grout..bobs ya uncle
     
  18. rogerk101

    rogerk101 Well-Known Member

    Many thanks for this detailed write-up of the two options. I have a few questions ...

    You seem to be suggesting either the LEH/KIAB approach (joists fixed to concrete base, P5 fixed to joists, WBP fixed to P5) or a new variant of my original floating approach (floating insulation, floating P5, WBP screwed and glued to P5, then SLC on top of this)? With the second approach, why would the SLC on top be better than on the bottom (i.e. directly on the concrete base)?
    For both approaches, do you really think I'd need 22mm P5 and 15mm WBP rather than just the waterproof grade 22mm T&G chipboard?
     
  19. Jimbo

    Jimbo Well-Known Member

    how about (top down)

    18 mm ply, screwed and glued and staggered over...
    18 mm ply, floating on
    celotex, laid directly on
    DPM

    Or you could use two coats of Black Jack and a SLC instead of the DPM if the bumps are too much to be taken up by the celotex.

    I can't see the advantage in mixing materials at the top at this would surely create thermal stress.
     
    rogerk101 likes this.
  20. Multiskillmaster

    Multiskillmaster New Member

    Any way you choose to do it, if it’s carried out correctly is good..what is easiest for you?
    I don’t know the severity of the uneven sub floor. Always best to correct it at the base...but then maybe you are in the realms multiple layers or mixing SLC with sharp sand to get the depths you need to level the floor out.
    The bostik is a great layer to tile on, no only a flexible reinforced layer but stuck fast and takes out the final imperfections.
    Jimbo is right you could use black jack, but it’s messy and would require 3 coats...rather than cut and lay a sheet of DPM..
    All chipboard is water resistant, not waterproof (impermeable to water)...leave a bit outside and that becomes apparent.
    Always 22 mm for floating, and new for me..18 to match in with existing floor boards..closer centres etc.. and yes for tiling 15mm ply is regs. It’s for stability, I do a lot of wet rooms and flex is eliminated by this method.
     

Share This Page