Uneven concrete floor - what's the worst that can happen?!

[Glenn]

Hello all, dumb question time

 

Laying a plywood floor over rigid celotex boards, themselves laid on an uneven concrete floor (say max 25/30mm humps and dips). What are the consequences in terms of noise and feel, integity, insulation value etc, if no attempt is made to level the floor by e.g. A bonded screed, or filling individual dips

 

More detail. Converting some sheds next to actual build. The 2 sheds are basically one unit, and will be a workshop and temp acvommodation/storage etc. Both have a typically roughly laid farm building concrete floor. All advice received and much online is built around assumption that end result is always a screeded, insulated floor. It is asserted a level floor is required before insulated boards are laid, but at the same time it is assumed that the screen on top of the boards will take care of levelling.

 

But I'm biased towards a timber floor in any case. My preferred build up would be dpm, insulation, then 2 layers of 12mms ply laid at 90 degrees to each other and screwed together

 

My budget is bookmarked for the actual build, so I am trying to identify the most effective way to achieve a good floor, without long drying time, at a good price, using a method I can DIY. 

 

To work that out I ask myself what would happen if I don't do sometning? What if I just finished and lay the boards, some may have voids, or sit over a hump, will I notice it once the stiff plywood layer is laid and screwed?

 

I planned to use a semi-dry cement/sharp sand mix in any excessive area. should that go over or under the DPM?

 

Thank you for indulging me. Please do shoot holes in my plan.

 

Regards

Glenn

 

 

[PeterW]

Just use dry sharp sand before the DPM and then lay the insulation. It won’t move after that. 

[Russell griffiths]

I’ve  actually just done that. 

what i did was,  find the worst bits and mark on the floor

buy some high build floor level compound and chuck it in the low areas. 

Use eps insulation instead, cheaper and easier to work with. 

Lay the insulation boards down and if you don’t like the amount they rock mark them up and sand out an area on the eps so it sits over the hump better. 

Tounge and groove chipboard all glued together so it acts like one big sheet. 

4x1 timber as a skirting board to pin it all down. 

Garage floor paint to keep out stains. 

 

Worked a treat, just done before lockdown so no pics I’m afraid. 

[Glenn]

Thank you both for your reassurance, much appreciated!

 

the extra weight of the chipboard, worth considering

 

Regards

Glenn

[Hydra]

Currently looking to do the same for a porch conversion - leveller left me with 3mm humps, mostly in the middle - 2 hours of grinding later it's better but any PIR slab on it is going to rock all over the place. 

 

I am a little worried that the sharp sand will move over time? Though I guess with a 100mm PIR slab and floor boards, it "shouldn't ?

 

Do I worry too much  How did yours turn out?

[Mr Punter]

55 minutes ago, Hydra said:

Currently looking to do the same for a porch conversion - leveller left me with 3mm humps, mostly in the middle - 2 hours of grinding later it's better but any PIR slab on it is going to rock all over the place. 

 

I am a little worried that the sharp sand will move over time? Though I guess with a 100mm PIR slab and floor boards, it "shouldn't ?

 

Do I worry too much  How did yours turn out?

 

If the humps are only 3mm you will not notice with the 100mm pir over.  Like The Princess and The Pea!

[Hydra]

I agree it doesn't sound much, though I have a smaller length of PIR I laid down as a tester, admittedly not a very accurate one - it rocked all over the show

 

Been researching and might use some sharp sand just for peace of mind, assuming a dry fit isn't satisfactory.