Laminate floor installation

Greetings,
I'll be installing a laminate floor over a concrete slab. The installation instructions specify that the subfloor must be level to within 2mm (they don't specify over what gap though).
I just spent some time trying to determine how flat my concrete slab is by placing a piece of string really taut and then measuring the gap between the string and the floor.
On the worst spots, the gap was a little over 2mm, perhaps 2.5mm.
Do I need to worry about this? How much is "too much"? I'm wondering if I'd make things worse by trying to fix these depressions (just a couple of spots in a 15' x 20' room).
Thanks.
-jav
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Javier Henderson wrote:

That's their 'out', if you have a problem. 2 MM is 0.0787 of an inch, or about 5/64". Find a floor in any house that is that level.
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If there is too much gap the planks could seperate where they snap together or become loose as time causes them to wear from movement.
I had a similar problem over vinyl and in a few spots where the traffic was low I doubled up the foam pad under those spots.
So far so good.
Tom

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Hi; Your floor needs to be level. So what does this mean? Take a single board, lay it across the suspect area's (make sure you put the underpad down also) and check for bounce/deflection. if there is very little if any at all, start installing. If you use a beter quality of underpad ie; Quietwalk felt, it will take up these little discrepancies. Trying to level the whole floor perfectly is a waste of time, money, effort and resources. Laminate when combined with a good underpad will make up for this. We install 200,000 sq/ft + per year of laminate and our crews use this as a guide for which underpad to use. If there are bad area's you can always use a floor patch cement, available at most lumber stores, it sets in about 35 minutes. Note; Because this is a basement installation, PLEASE make sure you have a vapour barrier installed or a certified underpad that incorporates an underpad. Cheap white foam sheets do not cut it and will void any relevant warranties.
Cheers and Cia
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From my experience, no.
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