Can You Install Cement Board Over OSB? (Solved)

Known in full as Oriented Strand Board, OSB is an engineered wood panel with versatile uses. It contains rectangular-shaped wood pieces that are attached using heat-cured adhesives.

OSB has got many features. It is resistant to distortion, warping, and deflection. It also has a strength equal to that of plywood. It can be used for structure and non-structural purposes.

Amongst the many uses of OSB, are you considering installing a cement board over it? Keep on reading to find out if that’s possible and if there are any issues you need to be aware of before proceeding.

OSB board

What is a Cement Board?

Before we can look at the possibilities of installing a cement board over OSB, we must define these two. We have already introduced OSB and some of its uses.

Cement boards are sheets containing cement and fibers. The primary use of a cement board is to be used as a tile backing.

A cement board performs exceptionally well as a tile backing since it features excellent water-resistant capabilities. With a tile backer such as a cement board, you are assured of preventing mold growth.

Why Would You Want to Install Cement Board Over OSB?

The main reason you would want to engage in such a project is to create a conducive surface for tile installation.

Installing tiles directly over OSB is tricky because when an oriented strand board becomes damp, it can easily come apart and ruin your tile installation project.

That’s where a cement board comes into the picture. With a cement board on the surface of OSB, tile installation will be pretty straightforward, and you are assured of maximum adhesion.

The theory here is workable. But is it possible to install a cement board over OSB?

Is It Okay to Install a Cement Board Over OSB?

You can install a cement board over OSB, but there are several products you will have to use. First, you will need to layer the thinset over OSB.

Thinset is an adhesive made using a mixture of fine sand, water, and cement. It is a common product used in tile installation. In this scenario, however, the thinset will go over the OSB.

What follows is the cement board, more thinset, and then the tiles can be installed. When you follow this procedure, you are assured of a successful tile installation job that will last for a very long.

As easy as the above procedure may sound, certain issues may pop up. OSB isn’t the ideal surface for tile installation. The use of a thinset and a cement board is more of a DIY trick. If you ask an expert, they will advise you to remove the OSB and leave the wall or floor empty.

This usually isn’t the best option for many homeowners, especially when you consider the losses incurred and the time used up. It’s even worse when all the walls in your home are sitting on OSB.

Is It Advisable to Use Thinset Over OSB?

As you can see from the method recommended above, the thinset comes first before the cement board. That means it will be in direct contact with the OSB.

Most people are usually reluctant about applying thinset over OSB because it contains water. However, OSB is water-resistant. Therefore, the occasional exposure to moisture won’t damage it.

What is considered wrong is installing tiles directly to OSB using a thinset. That will leave the OSB more exposed to moisture.

However, with a cement board in between, you don’t have to worry about the water in the thinset. That will be dealt with when the thinset dries.

The above method is highly recommended for homes or commercial properties where there is OSB on the floor or walls and the owners want to install tiles. As long as you get it right, there’s nothing you should worry about.

What about an Underlayment Membrane?

If you are constantly updated with the latest products in the construction industry, you may have come across underlayment membranes. These are new products that can be installed between the subfloor and the tiles.

The primary role of an underlayment membrane is to absorb the changes in the subfloor, which can affect the tiles on the surface.

Besides the above, an underlayment membrane is also an excellent alternative to a cement backer board. A perfect example of an underlayment membrane that can be used to install tiles over cement board is RedGard or Custom Building Product’s Wonderboard.

You can use either of these to bond tiles over OSB without worrying about damaging either. Please note that you can also use other underlayment membranes as long as they are waterproof.

Won’t the Cement Board Increase the Thickness of the Floor?

That’s bound to happen, especially when you consider the several layers of products that will be added. When installing tiles over a cement board, you need to expect a rise in thickness.

The first culprit to add thickness will be the cement board. Then the tiles will also add some thickness. Unless you are working on one corner of your home, you need not worry about uniformity when tiling an entire room.

Is Removing the OSB the Best Option?

Installing tiles on a floor or wall is much easier if there is nothing in between. Because all you need here is a cement board, and the project will be done.

If you are in a hurry, you can use a thinset to bond the tiles to the wall. The presence of an OSB complicates the procedure.

If you plan on tiling over OSB and don’t want to run into any issues later on, the best thing you can do is remove the OSB. As a result, you will be assured of a flawless project. The tiles won’t crack, nor will the OSB be damaged by moisture.

Even though removing OSB is the best option, it’s impossible for most homeowners. Assuming that your subfloor and walls are covered in OSB. How much time and resources will it take you to pull off such a project?

Most people usually have no other choice than to use a thinset and cement board or a waterproof underlayment membrane.

Cement board

Can I Use Ditra Instead of Cement Board Over OSB?

For those of you who have engaged in tile installation projects in the past, Ditra should be a familiar name. This is an uncoupling membrane that is commonly used for the installation of tiles. Ditra contains polyethylene which acts as a waterproofing membrane.

Ditra has been successfully used over OSB by many homeowners. If you ask any Schluter representative, they will inform you that Ditra is safe to use over OSB for tile installation. Many people have used Ditra over OSB and haven’t run into any issues.

If you want to have more options, here is another product that you can use on this project.

Do I Have to Worry about Leakages When Using Cement Board Over OSB?

Even though tiles can be installed in any room, they are most common in kitchens and bathrooms. There is one thing that these two rooms share – frequent exposure to moisture and water.

Before embarking on such a project, you may be afraid of water leaking through the tiles, and cement board, and reaching the OSB. We all know what happens when OSB is regularly exposed to water and moisture.

If you fit the cement board correctly and make sure that any openings are sealed, you don’t have to worry about moisture reaching the OSB.

Even though cement boards are not waterproof, they are water-resistant. That will also help prevent some moisture from reaching the OSB.

If you doubt the cement board’s ability to repel moisture, you can always use a waterproof underlayment membrane. These are more resistant to water and will ensure the OSB is safe from water damage.

Is It Wrong to Install Tiles Over OSB?

It’s not advisable to install tiles directly over OSB. However, you can be assured of better results when using the thinset and a backer board in between.

The same also applies when you use Ditra or a waterproof underlayment membrane. The topic of whether one can tile over OSB is filled with many contradicting opinions.

It’s essential to seek professional advice and conduct thorough research before following or listening to views shared by friends or colleagues.

There is nothing wrong with installing tiles over OSB as long as you use the recommended products and methods.

Can I Add Plywood Between the Cement Board and OSB?

The use of plywood is another excellent method of shielding OSB from moisture. If you have some, you can layer plywood on top of OSB. Then proceed to apply the thinset, cement board, and tiles on top.

The plywood will be exposed to some moisture from the thinset. But at least the OSB at the end will be moisture-free.

It’s important to remember that the more materials used in tile installation over OSB, the thicker the floor will be. Also, the plywood needs to be screwed into the OSB to avoid movement after installing the tiles.

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