Cement board is a good, reliable backer board that works well on both floors and walls. Keep in mind that most tile setters err on the side of caution and brush a waterproofing membrane on top of cement board when it is in wet areas like showers or tub surrounds.
Insulating behind shower walls improves moisture control, which in turn reduces the chances of mold growth. Apart from retaining heat and minimizing condensation, insulating behind shower walls also provides better acoustics by reducing annoying sounds from outdoors or between rooms. The whole point of this post is to get to this bottom line: Water containment on shower walls is important and a requirement.
Waterproofing on horizontal surfaces is absolutely critical. Contrary to popular belief, ceramic tile and grout, by themselves are not waterproof. Water can penetrate through cement-based grout and work its way through the substrate. To prevent water damage, you must install a waterproof membrane just below the tile bonding mortar as close to the tile as possible. Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions: the inner surface in colder climates and the outer surface in hot, humid climates.
In existing spaces, oil-based paints or vapor-barrier latex paints offer an effective moisture barrier. Ideally, you would remove the torn plastic. When you install a vapor barrier that has wrinkles or raised portions it is more vulnerable to tears. Should I use visqueen or plastic sheeting on the framed basement walls? No you should not, as plastic will prevent moisture from moving through the wall and will lead to mold and damage.
Our best practices are that the old vapor barrier is left in place and the new one is placed over it. The old barrier even if it does not cover the entire crawl space serves to provide some additional moisture blocking and also help protect your new vapor barrier from any rocks or debris on your crawl space floor.
HardieBacker is much more light, and it is also the best selling brand of cement board available. It is much cleaner because it does not have any glass in it. It allows for a smooth job with minimal mess. Use an appropriate waterproof or moisture-resistant backing material behind grouted tile or stone or segmented plastic or fiberglass tub and shower surrounds. Appropriate materials include cement board which has a cementitious core and glass mats on both sides to strengthen the board. You have several options to choose from when choosing a vapor barrier and each affects your waterproofing strategy.
First, you have vapor barriers that are installed behind your tile substrate, common materials that are used due to their availability and cost are, a continuous plastic sheeting with a minimum thickness of 4-mils, lb or 15 felt paper, some building codes require a minimum Grade B building paper to qualify as a vapor resistant barrier. The alternative to a vapor barrier that is installed behind the tile substrate is a liquid or sheet membrane that is applied over or installed on to the tile substrate.
Depending upon your choice of tile substrate, such as a backer board material, some manufacturers will not stress the requirement of a vapor barrier, such as Hardiebacker or Durock, in these cases it is left up to the local building codes and industry standards to determine the best choice. While other manufacturers advise against it, such as DensShield, which has a built-in moisture barrier.
For vapor barriers that are installed behind the tile substrate, the installation is quick and easy but there are some considerations to keep in mind. First, whether you chose a plastic sheeting or lb felt paper, when installing onto the wood studs, it is suggested that you use a minimum amount of staples to minimize any entry points for moisture. Ideally, the plastic sheeting should be one continuous piece, but where two pieces need to be seemed together, a water resistant tape can be used to adhere overlapping edges.
If you choose to install lb felt paper, the horizontal pieces should be continous that start from the bottom up, then overlap each other a minimum of 2 to 4 inches, encouraging moisture to exit into the shower area. Where a seam connects two pieces, there must be a minimum of 6 inches of overlap. A vapor barrier can be applied or installed over the tile substrate using a liquid or sheet membrane. There is a clear advantage of using a liquid membrane, it is relatively easy to apply over the tile substrate, along with the use of a fiber mesh tape, you can secure joints and changes of plane.
A sheet membrane has just as much of an advantage for ease of installation, but you gain the further benefit of continuity of thickness. The seams and joints still need to be covered with a fiber mesh tape but you will be left with a sturdy surface. The industry standard, as well as most local building codes, do not encourage the use of a vapor barrier behind and over the tile substrate.
If moisture reaches your vapor barrier behind the tile substrate it should have the opportunity to evaporate, this process is hindered when a second vapor barrier is applied or installed to the outside of the tile substrate.
In this case, there is less breathability to encourage evaporation, which ultimately could cause mold growth. A standard argument would be that moisture would never reach behind the tile substrate if a liquid membrane is applied or a sheet membrane is installed over the tile substrate. It is important to note that the wet area is inside the shower area, not behind the shower walls, therefore you need protection leading outward, not protection leading inward.
In some cases, you may not have a choice, your local building codes will determine what is or is not required. If you choose to apply a liquid or install a sheet membrane over the tile substrate, you would then be adding a vapor barrier by default.
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