Rises and falls in plywood like old subfloor

My old sub floor has lumps and bumps in it.

I have screwed down some 5.5mm plywood but I'm seeing rises and falls in the plywood as well.

Any ideas on how I get a flatter surface.

Going to be putting down solid wood on top of the ply.

Any help greatly appreciated as my wife is giving me grief to get this done asap

 

You need to level it with a flexible self levelling compound.


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Are you going onto old floorboards?

I normally sand the existing floor to remove the cupping in the boards and create a key. Then use a minimum of 9mm ply which is rigid enough not to follow any unevenness, when it's glued down any small voids are filled.

 

Thanks for this. Good options that I need to weigh up.. @merit - using self-leveling compound sounds too messy and more cost. @James - Got the ply free from my neighbors loft so going to try and use it. Sanding the floor could be an option but sounds like a big job.

 

The 9 mm ply method screwed down would be a good method, but if you have already layed 5.5 ply then you need to consider how much your building the floor level up, don't forget you still got the new flooring on top to go, maybe the appropriate latex poured all over and probably wouldn't bring level up so much, good luck .Mick.

 

I have had to pull up the existing subfloor and deal with high and low floor joists, to get it perfect.
Always remember the more weight added to the structure, the more reinforcement must be added, to hold it.