Installing sub-floor over uneven concrete floor

[elimn8or]

Hi, I have a room which is a conversion of an old garage. The concrete floor is about 2" lower at one end. I already tried using self-levelling compound but this ended up cracking. Ive taken that all up now so im back to the original gradient. What my current thinking is to batton the floor at 40cm intervals with 2x1 battons. At the higher ends i was thinking of using a SDS drill to dig channels to sink the battons into. These could be levelled in their channels using a sand/cement hard mix and fastened using the concrete self tapping screws. Obviously as a head down the gradient of the floor suface my batton height will need to increase but still applied to a level suface. Once battoned i would lay 18mm plywood sheets and fasten. This would give me a level sub-floor.

In the end I want to lay a floating floor consisting of fibre-boards for sound insulation and solid oak over it. this ive done before!

Can anyone tell me if ive missed something in creating a level floor surface or if there is a better/more-efficient way of doing it - im all ears.

 

[simoniris]

Is the floor lower because of subsidence - has the concrete cracked around the wall, is it clear that some of the 2 inches of brickwork above the slab used to be hidden by concrete? Are there cracks elsewhere in the slab?
If so you really ought to think about breaking out the whole slab and starting again.
By the time you've chipped channels in it you may just weaken the slab more causing it to move further.
If you break the slab out you could [and should] then put a membrane, insulation & new level reinforced slab in.
You could then loose lay a floating timber framework to fix your oak.

 

[noseall]

simoniris, garage floors are often laid with a deliberate slope, so fret not about subsidence.

have you looked at using firring strips (diminishing strips) to level up the floor?

 

[elimn8or]

Sorry - forgot to mention that the floor has a slope due to its construction - not subsidance

 

[elimn8or]

Additional - I will be making 1" channels at the upper end of the room. As i progress down the room these will get smaller and substituted with bigger batons. Is this a sound idea? Thanks for letting me know about "firring strips (diminishing strips)" - ill check em out after work today

 

[simoniris]

For some reason the image I had in my head was of the low end being opposite end to the garage door - strange the way the mind works!!

If garage is not too long / deep along the fall why not scribe a length of skirting or similar to the floor, trim it and use as a pattern and rip down some 4x2 or similar section timber to make your own furring strips to level the slope? Be quick, quick, quick with a decent circular saw. Cut enough to run at 450ctrs across the fall and noggin them together, fit oak boards directly on top?
Really can't bond with the idea of chipping out the floor on so many levels - why do you want to try to cut concrete?! It's about the worst job in the world!!

 

[elimn8or]

Agreed - i was dreading that part even though i have the tools to do it. I like the idea of making furring strips - i just need to find out what these are.

One last point - the highest part of my old garage floor contains the patio doors. Therefore, i can only go up a maximum of 2" including the new flooring. Therefore i suspect i will have to dig a couple of small trenches to at least lower the upper batons?

 

[simoniris]

What is the thickness of your new floor covering? Presume the 2" you have to play with is from threshold down to existing floor level, so 4" from threshold to lowest point at the other end?
You could still achieve this using 4x2 reg treated timber by ripping it down to 1" @ the top end to 3" at the other. That will give you an inch from the top of your joists to the threshold and remove the 2" fall. If you install the joists at tight enough centres [450mm max] and your floor boards are 18mm thick T&G then you can fit them straight to the joists without the need for counter battens. Only issue with this is that good practice with linear floor coverings is to lay them to the lightsource. If your french doors are the only source of light the boards will be running across them but it's no big deal really. Assuming french doors are at the top of the slope of course - it's those mental images again!!