Homeowners who want the assurance of protection against water and leaks should consider waterproofing the cement board before installing things like tile or backsplashes.
Cement board is a hardier option than other forms of backing boards but it isn't waterproof. Neither is tile or most other forms of backsplashes. Waterproofing them with a sealant or a membrane under the backer board are two effective ways to keep water from seeping into the walls.
Waterproofing cement boards is a fairly simple do-it-yourself project and isn't expensive either. It may take a little time and should be done during a remodel or construction since you are working behind the tile or backsplash.
What Are Cement Boards?
Cement backer board is a pre-fabricated unit for walls made of cement, silica, fibers like fiberglass, limestone flour, and water. It is an inexpensive way to make things like tiling, countertops, and flooring look better and more durable.
Cement boards reduce the change of rotting behind tile or flooring as well as protects wall studs and floor joists.
Why Do You Need to Waterproof Cement Boards?
The reason you want to waterproof cement boards is that you want to protect studs or joists underneath from all moisture. There are three ways to waterproof cement boards.
Both are effective and the choice of which to use depends on your budget, your time, and your preference.
One thing to note is that you will still need to seal tiles, backsplashes, and other types of things that are on top of the cement board to truly waterproof the area. Most of those things are porous. Even if they aren't, the grout between the tile isn't waterproof and moisture can seep in that way.
What Products Can Be Used to Waterproof Cement Boards?
There are several products for both membranes and liquid sealants that work well.
1. USG DUROCK Liquid Waterproofing Membrane
- Anti-fracture protection up to 1/8 in. (3mm) over shrinkage and other non-structural cracks
- Can be rolled, brushed, troweled, and sprayed
- Fast drying time allows for quick turnaround time
This is a liquid waterproof membrane that goes on the surface smoothly like thick paint. It can be applied with a brush or roller and has excellent reviews from those who have used it.
2. Laticrete Waterproofing Membrane Fabric
- Required for use with HYDRO BARRIER™ in coves, corner and changes of plain for waterproofing applications
- Can be used with HYDRO BAN ®for added strength
- Interior and exterior use
This fabric comes in solid white. It comes in a roll of 6" x 75' material. This membrane is a load-bearing, thin option designed to be used with ceramic tile, brick, and stone. It is a rubber polymer that is self-curing that forms a seamless waterproof, flexible membrane.
Waterproofing Membrane Sheets
1. JBC Concepts Waterproofing Membrane Sheet
- 100% polypropylene non-woven geotextile
- Waterproofing membrane for bathroom, showers, floors, walls, seams, corners, joints, steam rooms and all your wet area application needs
- Minimal build up at seams. Easily cut to form corners
These come in long rolls amounting to 36-inches wide and 80 feet long. Sheets are typically used in bathrooms as they can be used underneath porcelain tile, in the shower, or even underneath heated tile floors. It can also go on mortar under acrylic surround and works comparable to the fabric.
1. Liquid Rubber Waterproof Sealant
- Safe for you, your family, pets and plants
This product can be used on multiple surfaces whether they are indoor or outdoor. It is water-based and comes in black. It is a protective finish for planter boxes, roofs, sheds, basements, concrete, and other places.
Liquid Rubber offers 1000 percent elongation, which means it likely will not have an adhesion failure and is also environmentally friendly with no solvents or toxic odors.
2. Liquid Rubber Color Waterproof Sealant
- Safe for you, your family, pets and plants
- No solvents or VOC (volatile organic compounds)
This product can be used for surface leak repairs in both indoor and outdoor areas. It offers a water-based coating and is easy to apply. It comes in white and also has 1000 percent elongation to prevent adhesion failure.
How to Waterproof a Cement Board
There are simple steps to waterproofing a cement board. The first is in using a membrane. If using a cloth membrane. Some membranes are peel and stick. Those require a primer to be used on the surface before sticking it to the cement board.
While these are somewhat common globally, they aren't as well known in the United States. Most experts will suggest using a fabric membrane in the corners or hard-to-reach spots even if you use a liquid membrane across the rest of the boards.
Here Are the Steps to Install Fabric Membranes.
Here Is How to Install Membrane Sheets.
Here Is How to Apply a Liquid Sealant.
Liquid Sealants are meant to be applied like paint, so they are easy to apply. You just put some in a paint tray and use a roller to apply it evenly to the cement boards. It may go on thick so you may need to put effort into apply it thinner. It may require two coats.
Fully waterproof high-water areas like showers, kitchens, and laundry rooms will save you from many headaches later. It doesn't take much money or time to do it the right way in the beginning and that saves you money over the life of your home.