Depending on the age of your home and the extent of your bathroom remodeling project you may or may not have to remove the drywall or plaster lath that make up the surfaces for your walls.
If your home was built before 1960 and you will be doing more then just replacing a vanity and toilet then you should probably consider a total remake of your bathroom if the walls and floors have never been opened up.
In older homes it is very possible to find lead pipe in your bathroom along with other pipe that is nearing its life expectancy. Copper pipe will deteriorate from within and eventually cause dozens of tiny pinholes throughout its length. Another problem is calcification or buildup within the pipe of minerals that will reduce its water pressure flow rate. On the other side or waste pipe side of the bathroom Cast Iron pipe can break down over time and depending on the the quality of the pipe and the professionalism of the installer 50 years or longer ago it is not dependable to install thousands of dollars in new fixtures to pipes that can cause you problems.
Another consideration is the electrical service to the bathroom. Although you can install a home run to a whirlpool bath to provide the necessary circuit for the pump and heater you might as well look into what type of electrical products were installed. You definitely want circuits that can accept a GFI outlet and you want them rated high enough to provide all of the electricity you will need for any niceties that you are installing.
For this reason really dated bathrooms can do with a full wall and floor tare out.
After you have installed all your services you will want to seal up your walls correctly so your project will last for many years to come.
Drywall & Concrete Backer Board
There are two standard drywall type materials that you should use in your bathroom.
Whether code in your area demands it or not you should never use any standard drywall in a bathroom. The level of humidity is just too high to depend on standard drywall used in the rest of your home. You should always spend the extra $50 – $100 in materials and upgrade to water resistant materials.
Concrete Backer Board is used any place that direct water contact could occur and in areas where tile will be installed.This material comes in smaller sizes then standard drywall and it comes in two standard versions that you will see at your supplier.
The first is standard concrete board and this material is gray and looks like concrete has been used to form a section of drywall. The second is a higher processed material such as HardiBacker and this material is yellowish in color and very uniform in appearance. Which of these two types of Concrete backer you choose is not as important as using either of them instead of standard drywall.
Concrete backer board used to build shower stalls or bathtub surrounds should always be used in conjunction with vapor barriers and rubber membranes. Copper and Fiberglass Pans are also sometimes used depending on the design.
Water Resistant Drywall / Green Board is sometimes installed instead of concrete backer board around bathtubs but it should only be installed where direct water contact is not normal. When we say direct water contact that means walls that have been tiled too. Grout does and will fail over time and you can also have water seepage around fixtures or any place there is a puncture in the surface.
Green Board should be used on all of the walls including the ceiling in your bathroom. MOST drywall installers will tell you it is only necessary within a few feet of a shower or tub but the cost difference is so insignificant and the benefit higher making the only reason not to use it in a bathroom with a shower or tub a cost cutting measure for the contractor. They know they can get in and out and everything will be fine for a while. The fact is they would use it on every wall in their home so why not yours.
Rot Resistant Fiberglass Faced Drywall is also a higher performing product then the standard paper drywall used throughout your home. The Fiberglass covering on the drywall is designed to reduce the possibility of mold starting. This is a good choice but it is not the best choice in areas where water contact or high humidity is normal.
Installing Concrete Backer Board
You should follow the manufacturer’s directions on the type, placement and number of screw fasteners that your concrete backer board requires. Some people like to use a stainless steel or galvanized screw in water prone areas. This is probably a good idea but manufacturer designed screws are available for this product and should be used when available.
You should use a construction adhesive designed for water contact between the board and the stud to compensate for any gaps and provide a better bond. Install the board with the textured side towards the tile surface or smooth side to the studs.
You want to set the screw just deeper then the face of the board the same way you would with paper faced drywall but do not go through the fiberglass mesh. If you try to counter sink concrete backer board you will find the screw blows out the back and you end up with cracks in the material…. its not pretty so practice a couple before you get started.
Use a Fiberglass Tape not paper tape to cover joints between boards and you will also want to use a thinset mortar to fill the gaps.
Most manufacturers suggest 1/2 inch concrete backer board on walls and 1/4 inch on floors but many contractors will use two layers of concrete backer board to buildup partitions between the toilet and the tub or for shelf areas.
Backer board used on walls can go up alone but on your floor you must have a prepared substrate with plywood or luan as the attaching surface and thinset used as a glue.
On the floor you want to stagger joints when applying a second layer. This will reduce the possibility of water damage if your grout breaks down.
Cutting Cement Backer Board
It is important that you keep the dust to a minimum for health and cleanup reasons.
Cement board can be cut with hand cutters that look similar to a single blade utility knife but the blade has a special carbide tip to hold up to the concrete. If you are only doing a patch then you can get away with a couple cuts by using a heavy utility knife but be careful because they will tend to snap blades.
If you are a contractor that must cut a lot of this material there are special nippers that look like electric drills. I have never had a reason for using this type of cutter but it is defiantly preferred over a carbide diamond blade in a circular saw because of dust.
However if you need to make a plunge cut a 4 inch diamond tile cutting blade in a grinder will work well.
Remember that dust is not only a cleanup issue it is a health concern so whatever method you choose try to make as little of it as you can and wear a dust mask.
Note
I have worked in projects where a drop in steel bathtub was placed against a wall made of standard drywall. The owner of the home had years of trouble with tiles popping off and bubbling of the surface. The worst part of this under designed method is the mold that can build up in the studwalls. This is not the worst situation if the studwall the bath is attached to is a non load bearing wall but if it is supporting your home either on an outside or interior wall the mold will eat the studs and eventually cause catastrophic failure meaning anything from sagging roofs to collapses of walls or second floors.
The fact is if you get a poorly trained contractor that installs the wrong products or even installs the right products the wrong way you can end up with some serious expense that wont normally begin for weeks, months or maybe even a couple years after the bathroom remodel. This can cause you serious distress when trying to find a contractor who is most likely now out of business to sue them because you will end up having to replace everything if you need to do structural work.