Vacuum Dewatering ~ if the specification calls for a power float
surface finish vacuum dewatering could be used to shorten the time
delay between tamping the concrete and power floating the
surface. This method is suitable for slabs up to 300 mm thick. The
vacuum should be applied for approximately 3 minutes for every
25 mm depth of concrete which will allow power floating to take
place usually within 20 to 30 minutes of the tamping operation.
The applied vacuum forces out the surplus water by compressing
the slab and this causes a reduction in slab depth of approximately
2% therefore packing strips should be placed on the side forms
before tamping to allow for sufficient surcharge of concrete.
Typical Details~
Large Cast In-situ Ground Floors