How important is a vapor barrier when laying concrete?

[73super]

I was just curious.. I see people laying concrete floors with and without vapor barriers... How important is it to have one if you have proper drainage?

I seek the wisdom of all you wisenhymers!

Thanks much!

 

[Wardrum]

Wisenhymer #1 checking in. Spend the money and put a thick plastic vaper barrier down. You won't be sorry.

 

[bmwpower]

I would put down one at all costs. Water comes to the surface of a concrete slab via capillary action (small channels in concrete), so it only takes a little bit of water underneath, to allow it to reach the top.

If you're doing epoxy, VCT, etc., it's required.

 

[Steve in Mi]

Right, it is the capillary action that causes the water to be picked up and evidentially rise to the surface of the concrete floor. Capillary action is influenced to a large degree by the exposed surface area and long before poly was being used as a water/moisture barrier the folks that understood the relationship between surface area and capillary action would lay down news paper, tar paper and such to decrease the surface area on the bottom side of the concrete pour. Concrete poured directly on sand for example greatly increases the surface area (lots more capillary sites to **** up water) as each tiny grain of sand makes its mark/dent into the concrete on a microscopic level. Maybe helps to think of it like this - Point A to point B is 10 miles as the crow flies but as you travel the road between A and B there are lots of curves and hills so you may clock 15 miles on the surface.

 

[Steve in Mi]

Maybe my example wasn't so hot. Let me just say I'm in favor of the moisture barrier and 4 or 6 mil would definitely allow for a smoother pour underside (decreased surface area on sand) than a 50 gage Handi-Wrap or the flimsy (1/2 mil) drop cloth material. Now I'll stop.

 

[gotta56forme]

73Super,

I will be having my garage concrete poured over the next couple of weeks. One of things I requested was that we try to make the floor as dry as possible. I was told we would be using the 6mil plastic and that would be great plenty. As I won't be having a lift in my new garage, I don't want the floor to be any colder/damper than need be in our damp Seattle winters.

Scott/Gotta56forme

 

[73super]

Thanks for all the advice.. I'll definitely do it.

 

[Beegs]

Want to see capillary action in action? Take a paper towel and dip it in water and watch the water run up the paper. BTW if your floor guy doesn't want to pour over the barrier, get another floor guy.

 

[carcruse]

Around here the Building Code requires a minimum 6mil vapor barrier

 

[Steve in Mi]

The previous owner of my house appearantly believed in moisture barrier as the whole house is wraped in poly even the basement walls on the outside over the tar has it. It was built in 1961.

 

[z28toz06]

I didn't put plastic down but I layed 2" dow blue board down over the entire surface. I have radiant heat tubing so it was necessary. Do you think I should have placed plastic under that?

How long should I wait before putting an epoxy coating on the floor?

 

[Vicious_Cycle]

I know where the lift is going!

 

[Steve in Mi]

Do you think I should have placed plastic under that?

Right or wrong, I put 6 mil poly under my Dow foam. That was in 1981 maybe it's done differently today.

 

[thefairlaneman]

I was having a house built and to the builders dismay I was there almost every day checking his job, When it came time to pour the slab foundation they had plastic down first. I left before the cement truck came but came back to their surprize only minutes after it was dumped and the SOB workers had removed the plastic and hadnt had a chance to put it out of sight. I knew for sure I couldnt trust them. I soon backed out on the whole friggin deal and forsed them to return my deposit.

 

[threewindaguy]

I'll be pouring concrete within a week and don't really have a definitive answer on the moisture barrier question. I'm out here is sunny Arizona, so I'm not sure the extra money/bother is worth it. Any opinions? Thanks.

 

[bmwpower]

I was having a house built and to the builders dismay I was there almost every day checking his job, When it came time to pour the slab foundation they had plastic down first. I left before the cement truck came but came back to their surprize only minutes after it was dumped and the SOB workers had removed the plastic and hadnt had a chance to put it out of sight. I knew for sure I couldnt trust them. I soon backed out on the whole friggin deal and forsed them to return my deposit.

How'd you back out of the deal when they already started dumping the concrete?

 

[thefarelaneman]

This was just one of many things the crooks did while building my house. I documented everything (video ) and wrote a letter of complaint about each item.For exzample they used a hacket to cut holes in the roof for the vents, Read the blueprints wrong and had the ceiling height in the master bedroom to low by over one foot etc. I demanded my 1000 buck deposit back and said I would see them in court with my letters and video if they didnt cancil the contract so I walked away and found another house already built which I liked better. In fact the house I was building was completed and within a year I saw it on tv TORN APART BY A TORNADO. The subject of inferior contruction was brought up by the news media about this one builder.(KEN LOKEY HOMES.from texas

 

[bigdav160]

I'll be pouring concrete within a week and don't really have a definitive answer on the moisture barrier question. I'm out here is sunny Arizona, so I'm not sure the extra money/bother is worth it. Any opinions? Thanks.

I would answer "yes" for another reason. Your soil is so dry it will **** the moisture out of the slab before it's cured making it weak and brittle.

 

[Couchlump]

I can tell you what did happen when the concrete contractor pulled all of my vapor barrier out before pouring. Eight gallons a day is what my dehumidify takes out of the air in my shop. The contactor said that the concrete would not set up as fast with the vapor barrier in place. I did not care if it took a couple of months to set up as long as it was dry.
Took him to court and lost. The judge said that there wasn't anything in the contract that said that there had to be a vapor barrier in place at the time of pouring the concrete.

 

[Morrisman]

I can't see any reason NOT to put a damp proof membrane down (as we call it in the UK). It costs just a few bucks, is easy to find, easy to lay, and is already there, which means you're not wishing you'd done it afterwards.

If you have ANY moisture level in the soil beneath your concrete it will wick its way up to the surface, and you can forget putting floor paint onto damp concrete.