I am thinking about putting down a laminate floor over concrete slab. I realize I need a moisture barrier. I would like to know if I could put down a standard plastic type moisture barrier, then what is called a 2 in 1 barrier over top of that? Is there such a thing as too much moisture barrier? I live in Florida where it is always humid. Will I have a chance of moisture wicking up under the barrier(s)and getting trapped and not letting the slab breathe properly or am I just over thinking the situation?

Where is Home Care Club or Maintenance6 when we need them?? I think one or the other, or both, recommended taping a piece of clear plastic to the floor and after a couple of days, look at it and see if moisture has accumulated under it. If so, then there is moisture penetrating your floor, and you should install a vapor retarder on the slab before you install the laminate flooring.

You can buy 6-mil polyethylene in huge widths (like 20 feet wide) to minimize the number of joints. Whatever joints you do have should be lapped at least 6 inches and taped. The vapor retarder should also be taped to all walls and to all penetrations such as posts, columns, or pipes.

One vapor retarder is enough, and you want to trap moisture in the slab. If you let it "breathe", you may end up with serious mold issues under your laminate flooring.

If you do the test patch and it remains dry under the plastic, then I don't think a vapor retarder is needed, because there may be one already under your floor slab, where it should be, and if your test patch remains dry, the vapor retarder is doing its job.

How old is the house? Anything built in the last 40 years should have a vapor retarder under the floor slab. Earlier than that and it may or may not be there, and if it's 70 years old or so, there won't be one. (See? Us old goat architects are useful for something!) Good luck, and tell us what your test reveals.

Few questions.
Is the slab below grade on the outside of the house?

If the house is older the slab has dried out no issue. If its new cement you need to worry about moisture or those slabs that are below grade can get damp as well.

Richard is right. Only one vapor barrier. If you have more then one you risk trapping moisture between them. Results not good if that happens.However to clear this up we do not count the vapor barrier that should be under your cement floor. I am only talking about one vapor barrier on top of the cement floor. Do not layer them on top of each other. A two and one barrier is a vapor barrier with a foam pad as well. Offers moisture resistance as well as cushions the floor for slight uneveness. Also makes the floor feel softer says some companies.

To properly answer this question however you need to read and follow the manufactures instructions on the flooring your putting down. Every company has their own method of proper install. Some laminates are designed to be placed directly onto the cement floors. Some only on wood sub-floors. Some above grade only, some below as well as above.

My suggestion is to ask the sales person. Purchase the material that the company says will work with their product. If you do your own thing, or make an attempt at making it better and do it wrong. You will end up with no warranty on the floor.

Another question I would have is why laminate? Where are you placing it down? If its in a kitchen or bath. Forget about it. Any moisture or wettnes that gets on top of the floor needs to be picked up quickly. The seams on the laminate floor will suck up the moisture quick. The end result is the long edges of the floor will begin to swell and lift. The end result is a cupping effect on the boards which cannot be corrected. If your really concerned about moisture because of the area in which you reside, then laminate may not be a good choice. Personally I do not like the stuff. It makes the room loud and noisy. As the surface of the floor reflects all sounds.

Why cover the concrete you can turn the concrete into a piece of art for close to same price. Unless 1.you are spending $2 a sq. ft and plan on installing it yourself. 2.your concrete is in horrible condition with cracking and realy rough finish. A decorative concrete specialist in your area would be able to acid stain or dye your floor retaining the strength and durability in which concrete is known for.

There are other factors that come into play taking this rout but the longevity of a acid stained floor is second to none. Just make sure if you decide to go with a Acid stain or concrete overlay type product that they do a vapor test to make sure hydrostatic preasure is within reason.

Also being in the decorative concrete buisness myself I know of a few companies that sell vapor barrier material that can be applied with a paint roller.