If you're using Redgard, there's no need for a vapor barrier. Period.

What is better...using redguard or poly sheeting behind the cement board. I am thinking, wouldn't thinset work better at "biting" into cbu? Isn't putting redguard on the cbu kind of like adhering tile to "paint." When the redguard peels, off come the tiles? It just seems using thinset on cbu makes better adhesion? Why stick tiles to a thin layer of waterproof paint?

First, the thinset will "bite" into the Redgard just as well as it would into the CBU. Secondly, although it can go ON like paint, Redgard is anything but, and no, it won't peel off.

As for your first question, the poly behind the cbu is fine. But a surface membrane would be better.

Thanks for the help!!!

We had talked about using Redguard based upon some things from these forums, however we haven't settled on it yet. It sounds like it can be a pain, so I wonder if a poly lining behind the Hardiboard would be better, and then, if I remember correctly, the poly would overlap the tub edge.

Is Redguard better, or just as good as poly linings? Are there drawbacks between using one or the other? Do you use Redguard in someplaces, and poly in others?

Lastly, do you guys think I need to put it in other places outside of the tub area? I have heard of some different opinions on this issue.

Thanks again for making me smart!!

The redgard is better, being that it's a waterproofing instead of just a vapor barrier, but either one will work just as well. About the only time I'll use the Redgard is if the contractor put the CBU up before I got there and didn't use a vapor barrier (and actually, it's not Redgard I use, but Kerdi).

No need for anything outside the tub area. Matter of fact, you don't even need CBU. Sheetrock will suffice.

What about the ceiling over the tub and/or shower...should this be sheetrock or CBU, and is a vapor barrier needed? Do I need a soffit over a tub...not sure how a tiled ceiling would look over tub without a soffit? I guess I just tile over it and use bullnose to finish the edges. Do you tile over bare sheetrock, or should it be primed?

should this be sheetrock Could be or CBU, You could use that, as well, if you wish and is a vapor barrier needed? not on the ceiling.

mowers,

I'm not neccessarily disagreeing with Bill, but I'm looking to differntiate between two things, and possibly expand your horizons in the process:

1) The vapor barrier that acts as part of the thermal envelope of the house, and
2) The vapor barrier/drainage plane that goes into wet walls in showers and tub surrounds.

If the ceiling of the tub/shower is under your attic, and the attic is unfinished and unconditioned, then the bath ceiling is probably part of the thermal envelope of the house.

Now I can't see your house from here, but if the bath ceiling is part of the thermal envelope, then you'd want insulation and a vapor barrier/retarder in that ceiling.

Same with any of the bathroom walls that are exterior walls in the house. They may not need a drainage plane behind the tile if they are not in wet areas, but if they are exterior walls they may need a vapor barrier.

The location of the barrier depends on if you are in a heating or cooling climate.

Anyhow, I'm pobably confusing the issue...but I just want to make sure that you don't forget a vapor barrier for the thermal envelope of your house should you need one.

And like Bill wrote, you don't want two vapor barriers (Redguard and poly, for example) in one wall assembly, or you open up the possibility of moisture getting trapped between the two and not being able to dry.

Mongo

Actually, this is a bathroom that has an attic that is unfinished with insulation, and the long wall of the tub is an exterior wall. So while the long wall of the tub would be getting Redguard already..I guess the question is:

Do I put Reguard along the entire bathroom ceiling?

I am not planning on tiling the ceiling, but was going to put green board accorss the entire ceiling, but that can easily be change to wonderboard or Durock, then coat that with Redguard.

If the attic is insulated, then it has a vapor barrier as well. At least it should!

As such, unless you plan to one day turn your shower into a steam shower, there's no need to redguard the ceiling.

NOPE!!! Only drywall and then blown insulation. Figures! And we have 2 bathrooms on this floor...both without a vapor barrier.

My friend I had talked to had a good question; if we put a vapor barrior (or waterproof membrane) around the tub area, including the ceiling, won't that trap the mositure in the room? What he was saying is that while a whole house vapor barrier use to be the rule...he has been told (from various people) that it has become practice to allow the house to breathe, and not put a barrier around the house.

Your thoughts?

You don't need a vapor barrier for the ceiling-- only the walls. As for trapping the moisture in the room, this is why it's code in every jurisdiction I've ever been in that there either be a vent fan or an "openable" window in the bathroom-- to get rid of the moisture in the air. Now, here's a return question for your friend. Would you rather have the moisture in the room, where it can evaporate into the air and be removed, or would you rather that it get into the wall cavity where it can evaporate, but stay trapped, and cause all kinds of upset and discomfort, creating mold problems?

A vapor barrier protects the warmth and integrity of your home. Below was pasted from the internet. The friend is incorrect in his statement. New homes are very tight due to better barriers and very good sealing windows, but eliminating barriers causes bigger issues. Very tight homes you can leave a window cracked at times. Some newer heating/cooling systems have exchange systems built to pull in fresh air. I personally use poly sheeting as a vapor barrier because it is far superior to faced insulation. Regarding ceilings, check your local building codes, this may vary. But as mentioned below, attics can naturally ventilate as compared with a closed in wall.

Through a process called convection, warm air will always move toward colder air, meaning that during the winter the air inside your home is always trying to escape the house and move toward the cold air outside. Warm air also expands, and therefore has the capacity to hold more moisture than cold air -- moisture that is picked up naturally from inside your house. As the air cools, it contracts and loses some of its capacity, so the moisture is given off to cooler surrounding surfaces.

The result of all this is that warm, moisture-laden air is constantly on the move from inside to outside. As it leaves the warm interior of the house and enters the walls, attic, and crawl space, it cools off and gives up its moisture, which in turn can saturate the insulation and framing. The more moisture there is in the air and the more differential there is between the inside and outside temperatures, the worse the problem can become -- in the more extreme cases, the insulation is rendered virtually useless and severe rot can take place in structural members.

It is the purpose of the vapor barrier to prevent that movement or penetration of moisture from one area to another. Placed between the inside of the house and the insulation, the vapor barrier acts as a physical shield to repel the moisture and keep it from entering enclosed cavities where it can do serious damage.

Vapor barriers can be created from a variety of materials. The only requirement is that the material be resistant to moisture, which is indicated by its vapor permeance value, called a "perm" rating. To be an effective vapor barrier, a material needs to have a perm rating of 1.0 or lower. Common vapor barriers used with insulation include plastic sheeting, foil sheeting, and kraft paper that has been treated to achieve the proper perm rating.

Vapor Barriers in the Home

One of the most important vapor barriers in the home is the one between the wall insulation and the interior side of exterior walls. Because wall cavities are sealed and have no means of allowing accumulated moisture to escape, an effective moisture barrier is crucial in preventing warm, wet air from entering the walls.

For wall insulation, foil- or kraft paper-faced insulation is typically used. The insulation is installed between the studs with the vapor barrier facing in toward the house -- the one thing to remember about vapor barriers is that they are always installed between the insulation and heated portion of the house. The "wings" along the edges of the insulation are stapled to the studs to hold the insulation in place -- stapling to the face of the studs instead of the sides creates a more effective vapor barrier.

Another alternative for walls -- which is also commonly used in the enclosed cavities of vaulted ceilings where the pressure of warm air trying to escape is even greater -- is to place unfaced insulation into the cavities between framing members and then cover the insulation on the inside with plastic sheeting. The sheeting is stapled to the face of the studs or joists, and overlapped at all seams to prevent moisture penetration.

In today's construction, separate vapor barriers are typically not used between the home's interior and a ventilated attic. Most attics are insulated with blown fiberglass, which is relatively porous in comparison to the denser batt insulation used in the walls. The attic also has a continuous flow of air through it that is created by the roof and soffit vents, so moisture from inside the house passes through the insulation and is removed from the attic by the air currents. In areas of high humidity where moisture in the attic could still be a problem, a vapor barrier paint can be applied over the inside ceilings.

Another area that typically does not have a vapor barrier is the floor. Most of today's homes are now constructed with subfloors of interlocking tongue-and-groove plywood or other sheet materials -- waterproof resins are used in the making of the sheets, so the subfloor itself becomes an effective vapor barrier that protects the insulation below it. A vapor barrier is used, however over the ground under the house. Typically a layer of 6-mil plastic (1 mil = 1/1000 of an inch) that is laid directly on the dirt floor of the crawl space, the moisture barrier prevents ground moisture from entering the enclosed crawl space and wetting the insulation or the framing.

The misguided use of tight poly vapor barriers has caused untold millions of dollars of damage to North American homes.

One of the leading experts on moisture in homes on this continent, Dr. Joe Lstiburek, has succesfully campaigned for the removal of mandatory barriers from US Codes.

All the standard bumpf, as quoted above, concentrates on the importance of keeping moisture from entering the walls from the inside in the winter. What it overlooks is what happens in summer, when the air is moving from the hot humid exterior to the typically air conditioned interior--and gets trapped on the other side of the tight poly.

worthy-- are you talking about the exterior walls of the home, or are you talking about wet areas? If this is about wet areas, you're way off base. As for the exterior shell, I don't know enough about it to comment one way or the other.

Thank you tom_p for that read...that makes perfect sense. What my friend and I were talking about I think is what worthy was saying...about whole house wraps. I think that exterior wall vapor barriers are what are in "debate," where wet areas NEED a vapor barrier.

I have been talking to other friends that are GC and home builders in my area (Washington DC) and they basically said what bill_vincent & tom_p are saying:

Put waterproof stuff around the tub, don't worry about the ceiling (in my particular case because of the blown insulation & the attic which is open to the outside). Since we do have a exhaust fan that is enough for when someone is in the shower. The waterproofing Redguard will be perfect around the tub and under the tiles.

Since we are putting in a cast iron tub we don't really need Kerdi since we are not doing a "custom" tube with tiles. It was their opinion that Redguard is all we really need and Kerdi would be overkill and like bill says can be hard to install if you have never down it before.

This is my first bathroom, and what I find intersting is how much thought needs to go into this, to really do this correct because of how bad the consequence would be with water damage.

I mean, when I redid my kitchen, that was fairly straighforward, and I think the hardest part for me was making sure tiles couldn't crack based upon my floor, and to seal the grout :).

But this has been a really insteresting topic, waterproofing & vapor barrier istallation.

A whole house wrap allows the house to breath, while keeping moisture out. It is made to function properly. It is like gortex.

"All the standard bumpf, as quoted above..." Not quite so...

And...that is the purpose of a vapor barrier...to prevent air movement..if air cannot move, it will not move into the house, or visa vera. Without it, air will migrate through the wall cavity.

My GC just told me that the code changed in Florida and therefore he isn't going to put a vapor barrier on the exterior wall of the tub or shower, but only on the interior walls that line the tub and shower. Is that correct? So, should Redguard be used on all exterior and interior walls that surround the tub and shower?

I guess Florida must be the only place in the country that it's okay to go without the vapor barrier, then. If you go to John BRidge's forum, there are quite a few tile contractors in there from all over Florida. I think if you go in and ask them, they'll back up my sarcasm.

That said, if he's not going to install the vapor barrier, then yes-- I'd Redgard all the surfaces in the tub and shower enclosures.