# Vapor barriers



## SE18 (Feb 21, 2008)

Should a vapor barrier (sheet of plastic) be installed between the gravel and the concrete when building a concrete subroadbed? I'm planning to lay more track this fall.


The reason I'm asking, is that this weekend I'm building a concrete slab atop which will set a shed for my garden stuff, to clear the garage so I can set up a workshop there to continue building trains. The vapor barrier is recommended between the gravel and the concrete, though I'm not really sure what it is supposed to do (I know it stops moisture but don't know why that is important as I thought moisture is good for curing concrete).


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## Torby (Jan 2, 2008)

Cozad doesn't put one. If anybody know what he's doing with concrete, it'd be him.


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## Trains (Jan 2, 2008)

vapor barrier is for in the house not outside


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## SE18 (Feb 21, 2008)

thanks; 1 less headache


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## John J (Dec 29, 2007)

I don't do it and all my road bed is concrete. On the other hand there isn't much vapor in the desert


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## yardtrain (Feb 18, 2008)

The name says it all "Vapor Barrier. To stop vapors from below the earth to enter through small cracks in the concrete, normal use is in our area is to stop gases like Radon from entering your house thru cracks in your basement floor. See what the building code is in your town regarding storage sheds. But be carefull they may require a building permit. I needed a permit only because it was such a large shed and because it was on a concrete slab instead of building it with a wood floor on pillars with stone under it. If you do not follow their codes and inspections if any apply they can make you tear it down, if they find out about it.


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## SE18 (Feb 21, 2008)

Thanks, yardtrain, 

I may get a load of crusher fines for the sub-base of the concrete slab for the shed so I can use any remaining for RR ballast. I guess that would work just as well as larger gravel. The quarry charges $30 per truck load. They call it "dust." 

My slab will just be 4x6' as the shed is small (Lowe's)


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## yardtrain (Feb 18, 2008)

I don't think you want fines under concrete, maybe they will do a split load.


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## SE18 (Feb 21, 2008)

thanks; they HAVE to do a split load as I drive a Tacoma (they OK'd it)


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