Why on laminate flooring over concrete, vapor barrier is a must?

In documentation on laminate flooring is specified that you need a vapor barrier between the laminate and the floor. But I don't understand what are you protecting from whom? If laminate substrate is MDF, it will be damaged by any water that drops on the surface and filters between laminate junctions. Anything between laminate and concrete will be helpless. And the concrete I guess is impermeable.
Can anybody clear my mind on this?
Thanks in advance
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Faustino Dina
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Concrete is not impermeable hence the VB requirement
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This is new for me. I live in an unfinished concrete floor house. I'm considering put a laminate floor or other type of flooring but I never was concerned on the permeability of the concrete. May be the humidity of the basement (the humidity around the house is high 'cause near swamps) is gasing me through the floor? I'm serious about this.
Thanks Faustino
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Humdity is made up of moisture, and if the air you're breating isn't "gassing" you, neither is the humidity in your basement. About the only thing the could "gas" you thru your foundation is radon gas.
Vapor barrier is recommended for laminate flooring to keep moisture off the underside of the flooring, which can make it mold and rot. That's all.
AJS
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Concrete is anything but impermiable. The thing you're potecting is the Laminate from water that can come up throught the concrete.
John
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And how about water that can filter from the laminate surface, for example an accidental drop of water on the surface. My question is: Is the glueless laminate floor junction designed to avoid the water to reach the laminate substrate?
Thanks for your response Faustino
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