Vapor Barriers & Underlayment


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Old 07-07-21, 10:04 AM
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Vapor Barriers & Underlayment

I am going to install laminate by Traffic Master from Home Depot in a guest Bedroom over concrete (40 years old). I purchased the underlayment from HD also and was told it was premium and would provide the vapor barrier. The brand is Ultra Seal Floor Muffler. It says it provides superior moisture protection. I just want your advice on whether or not it will act as the vapor barrier? There is no evidence of needing a vapor barrier, but the flooring instructions says to use one. Is there a top and a bottom to this underlayment?
 
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Old 07-07-21, 11:23 AM
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Jameswil,

You can surely research that product on your own. They have a product video on YouTube. That video states a standard for applying floor coverings over concrete. The concrete moisture content must not exceed 3 lbs per 1000 sq ft in 24 hrs.

This number can be verified by a cup test. Here is an example of a test kit you could use: https://www.amazon.com/Moisture-Test.../dp/B0078KMKCG

This simply ensures that you don't cover up a wet floor, or a floor that is too wet. For example, some people may have had flooding... and the concrete looks dry, but is it dry enough? You don't want to out a vapor barrier over it if it isn't dry enough. Or you may have a wet basement. Or a slab foundation that wicks moisture around the perimeter of the room.

Testing will ensure that nothing will go wrong when you apply your vapor barrier. And yes, it is a vapor barrier, provided you install it correctly. And yes, there is a top and a bottom to it, as you would see in the video by the way the film works at the seams.

 
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Old 07-09-21, 05:32 AM
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Why do they want 2" up on the wall where you are going to start? Do you trim this before you start laying flooring?
 
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Old 07-09-21, 06:26 AM
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No, you trim it after you lay the flooring.
 
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Old 07-09-21, 10:11 AM
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If the vapor barrier is going up the wall for 2" how do you use the spacers to maintain the 1/4" gap with the floor and wall? Wouldn't the vapor barrier be in the gap?
 
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Old 07-09-21, 12:00 PM
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You turn it up the wall 2" so it runs up the drywall or baseboard. You press it into the corner so it makes a 90 degree angle. Then you put your spacer block down. Then you put the floor down. After the floor is down, you cut it off. I'm unsure which part of that you don't understand?
 
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Old 07-09-21, 12:13 PM
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What I don't understand is it seems to me that the thickness of the underlayment would be added to the spacer block since it runs up the baseboard and thus the gap would be larger than the desired 1/4 inch. The spacer block would touch the laminate board and the underlayment would touch the back of the spacer block and be in between the baseboard and the spacer block making the gap be the 1/4 inch spacer plus the thickness of the underlayment. Maybe that is alright, but the gap will be something like 3/8 or a little more.
 
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Old 07-09-21, 12:45 PM
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You are splitting hairs. Just follow their directions.
 
 

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