Cement boards are the backer of choice when it comes to wall-tile applications in areas that are exposed to water and high amounts of moisture. You may be wondering, though, can you put cement board over OSB?
You can put cement board over OSB if you are installing tiles in an area that is exposed to water or high levels of moisture. Cement boards are water-resistant and are not prone to mold or shrink like OSB. Cement boards will also provide a flat, smooth surface for tiles.
Cement boards are excellent to use when installing any type of tile. The strength and smooth, level surface of cement boards make it ideal when working with tiles that are less forgiving, such as glass or onyx.
The most popular reason for using cement boards is their water-resistant properties. Cement board does not have organic materials, like OSB, so it is not prone to mold and will not shrink or decompose.
Whether you are starting a project that is inside or outside, you can have the confidence that your project will not only look great but will withstand any moisture and mold issues and last for years to come.
Cement board is an extremely strong sheet made of cement and fiber-containing cellulose that also has excellent water-resistant capabilities. It is typically sold in 4 x 8 sheets that range between ¼ inch and ½ inch in thickness.
Cement board sheets resemble sheets of drywall but they are much stronger and have water-resistant capabilities that drywall does not have. Cement boards are readily available in big-box home improvement stores and are relatively inexpensive.
When doing your research on cement boards, you no doubt learned that there are two types of cement boards. A close relative to regular cement board is fiber cement board.
Fiber cement boards are very similar to regular cement boards. They, too, contain cement and wood fibers but also have sand as an added ingredient. The addition of sand makes them more brittle so care needs to be taken when using screws too close to the edge of the board.
Should You Put Cement Board Over OSB?
You have educated yourself on what cement board is, and which type of cement board to use, but now you are wondering if you should use it. Should you put cement board over OSB?
You should put cement board over OSB if the OSB is in good condition and is not damp. Damp OSB will lose its structure and not provide the strong support the cement board needs. Apply a thin layer of thin-set over the OSB to provide a waterproof seal before installing the cement board.
A cement board’s ability to withstand exposure to moisture makes it the ideal ingredient when installing tile, especially in a bathroom, as a backsplash, or anywhere else water and moisture are present. Even the ceiling.
OSB is capable of handling some amount of water exposure but it does not provide the level of water and moisture resistance you need. You also need a smooth, level work surface when installing tile. Cement boards provide you with both.
What Tools Do You Need To Put Cement Board Over OSB
Before you start your project, it is important to make sure you have all the correct tools to start and finish the job. What tools do you need to put cement board over OSB?
The tools needed to put cement board over OSB are your standard drywall tools: a T-square to mark your measurements, a drill driver, a utility knife, cement board screws, self-adhesive joint tape, thin-set mortar, a bucket, and a ¼ inch notched trowel.
Unlike regular drywall sheets, cement boards cannot be attached to OSB with standard drywall screws. You will need to use concrete screws or screws that are designed for masonry projects.
Regular drywall screws will eventually corrode, compromising the strength and stability of the cement board. Concrete screws have a specialty corrosion-resistance coating, ensuring the strength and longevity of the cement board.
Do not fasten the screws too deep into the cement board. Going too deep into the cement board will compromise the cement board’s structure. The screws need to be flush with the cement board face.
Cement board sheets can be cut with a utility knife, much like sheets of drywall. However, if you are using large sheets of cement board it is recommended to use a hand saw, circular saw, or multi-tool.
Use a blade that is carbide-tipped and designed to cut masonry products. Masonry blades will last longer and will ensure a cleaner cut.
What Preparations Do You Need To Put Cement Board Over OSB
You have your cement board and all the tools you need. Now you are ready to begin your project. What preparations do you need to put cement board over OSB?
When preparing to put cement board over OSB you first need to make a plan for your installation. Make a rough layout of the area you are covering and of the size of cement board sheets you need. Offset the joints between the cement board sheets and the OSB.
Proper planning and placement of the cement boards are the most crucial step in ensuring your finished project is one you can love and admire for years. The time and patience are worth it.
How To Put Cement Board Over OSB
You have all the tools you need and you are now ready to begin. The following 8 steps will walk you through how to successfully install cement board over OSB.
Step 1: Safety First
Before starting any project, the most important items to have on hand are the ones that will protect you personally. When it comes to working with cement boards, you will need eye protection, a dust mask, and cut-resistant gloves.
Cement boards are similar to drywall boards in that very fine dust is produced when the boards are cut. This dust can be extremely irritating to the eyes.
Copyright protected content owner: ReadyToDIY.com and was initially posted on January 18, 2023.
If you are working in an area that is not well-ventilated, it is best to also wear a dust mask so you do not breathe the dust in. Wear a mask that provides a tight seal around the nose and mouth.
Step 2: Cutting The Cement Board
Cutting the cement board to fit the area you are working in is the best way to make sure not only that you have enough cement board for your project but also to help the project progress smoothly.
Cement boards can be cut with a utility knife. Use a T-square to mark your measurements and ensure you get a straight and clean cut. Make two or three passes with the knife along the measurement line and then snap the waste area of the board.
Step 3: Mixing And Applying The Mortar
Thin-set mortar dries slowly so there is no rush or stress when using it, however, it is best to only mix enough for what you will be using. No specific brand of mortar needs to be used.
Using the smooth side of the ¼ inch trowel, spread enough mortar to cover one cement board sheet at a time. Use the notched side of the trowel to ridge the mortar, leaving parallel ridges of mortar for the cement boards to adhere to.
Copyright article owner is ReadyToDiy.com for this article. This post was first published on January 18, 2023.
Step 4: Place The Cement Boards
While the mortar is still wet, place the cement board where you want it. The mortar dries slowly so if you need to readjust the board, you have the time.
There is no right or wrong way to run the cement boards. The most important thing to remember when laying cement boards is that they should never touch. Always leave a ⅛ inch gap between each sheet.
Once the first cement board is laid, repeat step 1 and cover the next section with mortar.
Step 5: Secure The Cement Boards
Using masonry or cement board screws, attach the cement boards to the OSB every 6 to 8 inches. Do not place screws closer than a half inch from the edge of the boards. Make sure the screw heads are flush with the cement board.
Step 6: Apply Self-Adhesive Joint Tape
Cement board tape is not the same as drywall tape. Cement board tape is a special alkali-resistant tape that will adhere to the mortar. Make sure the tape adheres to the cement board before proceeding to the next step.
Step 7: Fill The Joints
Use the flat side of your trowel to fill the joints between each cement board sheet with mortar. Smooth the mortar out so that it extends a half inch beyond the joint. Unlike drywall mud, the mortar does not need to look nice. It only needs to be flat and smooth.
Step 8: Wait
It is tempting at this point to jump into installing the tile but you need to wait 24 to 48 hours before you begin laying any tile. If the mortar is not dry, the strength of the cement board’s hold will be compromised.
You can put cement board over OSB if the OSB is in good condition and has not been damaged by proper water exposure. Apply a thin layer of mortar over the OSB for the cement board to adhere to. Attach the cement board and OSB with masonry screws every 6 to 8 inches, leaving a ⅛ inch gap.
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ReadyToDIY is the owner of this article. This post was published on January 18, 2023.