Can You Use Mastic On Cement Board? (Explained)

Before any tile installation project, you must gather the tools and products needed. Mastic is one of the products that come in handy in tile installation.

It is a ceramic, glass, and porcelain tile adhesive often used alongside thinset mortar to stick tiles to floors and walls.

On the other hand, cement board is considered the best substrate for tile installation. Tiles adhere better and for longer when installed over a cement board.

If you intend to lay tiles over the cement board, you may be wondering – can I use mastic over the cement board?

This article will explain whether using mastic on cement boards is advisable and share more information about using these products for a successful tile installation job.

Cement board

Can I Apply Mastic on Cement Board?

Cement board is one of the most common substrates for mastic. Mastic is mainly used for tiling on walls and low-traffic floors. Therefore, it can be applied over cement boards such as Durock, Wonderboard, and HardieBacker.

Mastic is even more ideal for use on cement boards in vertical tiling because of its strong adhesive properties. In such a scenario, mastic prevents tiles from gliding or falling off a cement board wall.

Therefore, if you are installing tiles over cement board and would like to increase the level of adhesion. Feel free to use mastic alongside thinset mortar.

Which Side of the Cement Board Should Mastic Be Applied To?

When using cement board as a substrate for tile installation, you are advised to install the cement board with the rough surface facing up.

The rough side of a cement board is the ideal side for you to apply mastic on. The texture helps with adhesion, and it prevents the slipping of tiles.

However, for most cement boards such as Durock, the manufacturers agree that mastic should be applied on either side of the board. But to ensure maximum effectiveness, the rough and textured side is ideal for mastic application.

Can You Use Mastic on Cement Board in Wet Areas?

When installing tiles, you must identify whether that area will be exposed to moisture. Tiles are very poor at keeping moisture away from the substrate.

The good news is that cement boards are water-resistant. Cement boards will hold up their shape regardless of how frequently they are exposed to moisture.

Please note that cement boards are water-resistant and not waterproof. They will let water and water vapor pass through. This is something most DIY builders tend to forget.

The above can’t be said for mastic. If you are using mastic to adhere tiles over a cement board, please avoid using the former product in wet areas. It’s not just mastic. Most tile adhesives don’t do well in high moisture areas.

Mastic will be dissolved by moisture, losing its strength over time. That can lead to tiles falling off, especially if installed vertically on a cement board.

Even though mastic adheres well to cement boards, the combination of these two products shouldn’t be used around wet areas because mastic is weakened by water. Wet areas, in this case, refer to the bathroom or kitchen.

Other than Cement Boards, What Else Can Mastic Be Used On?

Before we move on from the above topic, we need to mention what mastic can or can’t be used. This information is very useful, especially if you consider using mastic in the future.

We have already mentioned that mastic adheres well to cement board. You can also use it on concrete, plywood, and interior drywall. In the latter, however, you should rough up the surface with sandpaper for better adhesion.

Besides the above, mastic should never be used on parquet, particleboard, veneered plywood, and hardwood.

You should also avoid using mastic on high-traffic flooring. Knowing the ideal substrates for mastic is crucial as it ensures you use the product correctly.

Mastic vs. Thinset Mortar – Which is Better for Cement Boards?

In tile installation jobs, thinset mortar is the go-to product for sticking tiles to a cement board. So, is there a difference between mastic and thinset mortar? When should you use mastic instead of thinset mortar? Keep on reading to find out.

Thinset mortar is ideal for most tile installation jobs over cement boards. Compared to mastic, it has a shorter curing time.

However, when installing tiles over a vertical cement board, you will benefit more from the immediate adhesion offered by mastic.

Unlike thinset, mastic grabs onto the tiles, making it better for use in installing tiles over vertical surfaces such as walls.

Another critical difference between mastic and thinset when installing tiles on cement board is that the latter has some leveling properties.

If you have been installing tiles for a while, you are aware that sometimes, you are forced to fill in depressions on the cement board, especially on the edges or seams.

Thinset mortar features ‘build’ properties which make it ideal for such scenarios. Unfortunately, mastic can’t be used to level surfaces. Mastic may have better adhesion for vertical tiles but doesn’t do well in high moisture areas.

We have already explained what may likely happen when mastic is used with a cement board on shower floors, bathtubs, and swimming pools.

With thinset mortar, there is no limit on where you can or can’t use it. It is perfect for dry and wet areas. This is one of the reasons many builders prefer thinset over mastic.

How Long Does Mastic Last on Cement Boards?

When used as a tile adhesive, mastic can last for over a decade on cement boards as long as it’s correctly applied and sealed.

On a dry area, mastic will do just fine. It can even last for more than 15 years on a cement board. Mastic’s number one enemy is water or moisture.

Regular exposure to these elements leads to quick deterioration of the mastic, and if it weakens, the tiles can begin to chip off on their own.

If you are considering using mastic on a cement board, ensure that you don’t do it in a wet area or high-traffic floor. If possible, seal the grout, and the mastic beneath should do its job without interference.

Can You Use Mastic with Cement Board on a Shower Floor?

No. Even if paired with a strong substrate such as cement board, it will cause tiles to delaminate. The shower floors are constantly getting wet.

Even when you use layers of sealant, some moisture will still escape through the tiles and reach the mastic beneath. This is inevitable. For tile installation on shower floors, stick to thinset mortar and cement boards.

Is It a Good Idea to Use Mastic on Cement Board?

Mastic is an old-school tile installation product. But that doesn’t mean it’s no longer useful. Many professional builders still use mastic to stick tiles to cement boards.

You already know the properties of mastic from our above guide. As we wrap up, we would leave you with a professional answer on whether it’s a good idea to use mastic on cement boards.

First, mastic is more beneficial when used on vertically installed cement boards in dry areas. Thanks to its strong adhesive properties, it ensures that tiles don’t fall off during installation on cement boards.

Mastic is easier to spread and doesn’t require mixing before application. As a result, it ensures the quick installation of tiles on cement boards.

However, mastic doesn’t last as long as thinset mortar. Being an organic adhesive, it may facilitate microbial growth inside your walls.

Also, there are risks when it is exposed to moisture. There are two types of mastic; type 1 is more water resistant than type 2. You should lean more towards type 1 mastic if you must use a tile adhesive on cement boards.

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