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Levelling floor with Shims

Discussion in 'Floors, Stairs and Lofts' started by MatFinish, 3 Aug 2021.

  1. MatFinish

    MatFinish

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    Ultimately I am aiming for engineered parquet flooring, however my existing floor has a slight bowl shape and the corners to corner is far from level. About 30mm over 4.5 meters.
    Its an 1860 build so I think its no surprise nothing is square and level!
    But I am looking for advice as to the best way to level the floor ready for the parquet installation.

    I have taken the floorboards off. The joists seem to be in good condition. I have had sound insulation installed so that rules out sistering the joists. Attached photo.

    My idea was to add shims on top of the joists, then lay plywood onto these shims to create the new subfloor.
    Could I use plastic levelling shims screwed into the joists at regular intervals for a job like this?


    It seems like a really simple solution compared to cutting shims from wood, or am i missing something?
     

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    Last edited by a moderator: 3 Aug 2021
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  3. KenGMac

    KenGMac

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    MatFinish, good evening.

    Can I suggest you use strips of, hardboard, and if needed? plywood of varying thicknesses?

    Both materials above are quite resistant to being compressed and as such will work, as well as being cheap but effective?

    Ken.
     
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  4. Keithmac

    Keithmac

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    I would have though the floor would bounce if you used plastic packers.

    For me I'd be using long strips of wood to keep as much support from the joists as possible.
     
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  5. Lower

    Lower

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    Why don't you sister the joists with joists that are level?

    Edit: Too late. I see you've already installed the insulation.
     
  6. JobAndKnock

    JobAndKnock

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    As others say, conventionally, you would sister the joists. Doing it that way makes it far faster and easier to get a series of flat, stable surfaces to fix your sub-floors to.

    With the best will in the world, using plastic packers it will be slower and more difficult to get a level "surface" to fix your sub-floor onto. There will also be a lack of continuous support beneath the sub-floor which might lead to dips forming in the plywood as well as making is more likely that you will subsequently get problems with creaking or cracking sounds eminating from the sub-floor due to insuffucient support beneath the plywood. Also if you don't fix through the plywood and the packer stacks you can end up forming hollows where the unsupported screws are as well as there being a chance that the packer stacks come apart and drop out

    This is why joiners sister joists
     
  7. MatFinish

    MatFinish

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    Thank you for the suggestions.
    Unfortunately I had sound proofing put in. I wasn't aware how uneven the joists were until after this was done.
    I really don't want to pull it all out as it was pretty expensive.
    Similar to @KenGMac mentioned, I have seen videos of people making long strips of wood fitted to the top of the joists. It looks very time consuming but is it a viable option?
     
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  9. JobAndKnock

    JobAndKnock

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    If the difference is minimal (e.g up to a 15 to 20 hollow in the middle of the floor) you can take that out by simply installing the plywood sub-floor directly onto the joists (glued to joists with a low expansion PU glue and screwed down) and then screeding with a self levelling compound to level it all up before installing your engineered flooring.

    Similarly you can deal with a floor which slopes to one side or one corner by building a (temporary) plywood dam and doing the same sort of build-up.

    Where the out of level is greater than that you either need an SLC which allows a greater build or you are into cutting tapered shims to fix to the tops of the joists. My experience in older buildings is that the out if level fall often isn't consistent, making cutting tapers which produce a consistently flat sub-floor problematic

    How far out are your joists?
     
    Last edited: 4 Aug 2021
  10. MatFinish

    MatFinish

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    @JobAndKnock There is a maximum difference of 30mm.
    You are also right in thinking the 'off levelness' isn't consistent, this is what made me consider plastic packing shims.
    I don't really want to use a levelling compound, I feel like its not a great long term solution. Must be a real pain for someone needing to do the floor in the future.
     
  11. Notch7

    Notch7

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    you could make plastic shims and plywood strips work - it would be rather time consuming, but doable.

    to make it solid, you could use frame sealant in the gaps.
     
  12. JobAndKnock

    JobAndKnock

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    All you do in the future is to smooth the floor off and put another thin layer of SLC over it if needed. Seen this done time and again on high traffic/load commercial jobs. It really isn't difficult.
     
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  13. Keithmac

    Keithmac

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    You can get 3.6 meter flat roof wedges (timber firrings?). Maybe rip these in half?.

    As said above some form of leveling compound is probably your easiest bet though.
     
  14. Mr Chibs

    Mr Chibs

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    Flexible SLC.
    Not the cheapest way, but probably better than faffing with firring strips.
    Shims etc may lead to creaking.
     
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