I love vapor barriers.
They never rip.
They have such a high R value that they stop the concrete from forming condensation.
They never trap water in between them and the concrete, along with sand and silt that holds moisture.
But of course, there are a few things that I don't understand.
If you put a piece of concrete in a puddle of water, how come the water never works its way up to the top of that piece of concrete?
When there is a crack in a slab that does not have a vapor barrier, and it's raining outside, why doesn't the water come in through that crack?
If you pour a cup of water on top of the concrete, how come the water never goes down through the concrete? just up from the ground to rest on the top of it?
If a slab with a house on it doesn't have a vapor barrier, why does water work it's way up through concrete in the garage/shop, but not inside the house and ruin the carpet?
OK, so I'm not being serious and I already know that nobody will answer my questions if they already believe that water comes up through the ground and through the concrete to rest on top of the concrete. I remodel homes and cut into concrete slabs fairly often. I've seen homes with vapor barriers and I've seen them tore and holes wore through them. I'm sure it's just the homes here in East Texas that has that happen to them, but the funny thing is that they don't have any moisture on top of the concrete. Another personal observation is that when replacing bathtubs, I never find any moisture on top of the concrete, yet there is a big hole under the tubs for the drain. Tubs almost always have pretty big gaps around their drain lines because it's so hard to get it just right when doing the rough in on the plumbing before the slab is poured. This is just another example that proves to me that water isn't coming into buildings from the soil under the building.
I think the vapor barrier has it's place and is actually very important when needed. Somehow it's become a wonder cure for things that don't exist, and it doesn't have anything to do with. The reason for it is to keep moisture IN the concrete when pouring a foundation. Concrete needs to keep it's moisture level for a certain amount of time to cure properly. If you pour concrete over porous or very dry souls, the moisture in the concrete will seep into the soil and out of the concrete. This will make for a weaker pour. The vapor barrier keeps the water in the concrete.
If you need it, then it's a great idea. If you think it's going to stop water from coming up out of the ground and forming puddles or wet areas on top of your concrete, spend the money for piece of mind. It's your money. But it's doesn't actually accomplish this.
Eddie
But from Eddies Post....a vapor barrier doesn't seem like a big deal except when used to slow the curing process....which seems to me to be the biggest advantage. Then too.....just closing the overhead door on my new shed will greatly slow the curing process by keeping the sun off the concrete and by slowing evaporation....probably much like keeping it covered.
