Glue and level plywood on screed

[Useroftheforce]

Hi - I have a small section of floor that is screed.
small = 1400 X 340 mm.

The front of the screed is 23mm below the desired finish hight. The screed is not level and falls away evenly to a hight at the rear of 35mm below the desired finish hight.

I wonder what the best way to affix a section of 18mm exterior ply to this screed would be.

Most the products I have found come in quantities way oversized for this sort of problem.

So far as I can tell a glue would be insufficient.

It needs to be solidly stuck as it will form a section of an subfloor onto which a solid oak floor will be laid. So drying time is a factor too.

Cheers.

 

[mac391]

Screw batten to the front and back then fill in the middle and cover with 12mm ply. i.e cut or plane a batten down to 11mm (for the 23mm end) and similarly a batten of 20mm (for the 32mm end) and use a string line to get measurements for any bettens inbetween. Lay 12mm ply.