for resilient sheet or tile isntalaltion, it isnt a requirement, however, the floring wil ltelegraph the inconsistencies in the slab and will show waviness.

for laminate/wood flooring, they are heigh tolerances the floor waviness can not exceed. Check with your manufactuer.

A common tolerance is 1/8" (inch) in 6' (feet), which means that any two points on the slab can not be over one eighth of an in in 6 linear feet in any direction. This can be tested with a level, straight edge, or very straight (perfectly straight) 2"x4" laid on edge.

It can be repaired/prepared two ways.

Instalaltion of a portland-cement-based Self Leveling Compound (SLC):

http://flooringworld.org/floorsearch.php?query=self-leveling+compound

some of the better known brands include:

Ardex Self Leveling Compound (k-15):

http://flooringworld.org/floorsearch.php?query=ardex+self-leveling+compound

Dependable wearflow and skimflow rs/es/lc/lite blended portland blended cements

http://floorprep.com/products.html

the second way is to screed patch and/or use a diamond grinder to grind the highest spots and patch in the low spots using an alluminum masons screed or a very straight 2"x4" on end. Use portland cement based floor patch. The idea here is to ride the screed over the high spots while pouring patch in from of the screed, which fills in the low spots, creating a flat floor without the waviness.

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There are two ways to do any job.

The right way and the wrong way.

Do it right everytime.

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http://flooringworld.org/

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