Do You Need A Vapor Barrier Behind Cement Board?

Installing cement boards on your walls requires further thinking about what's best for it. If you are wondering if it is necessary to include a vapor barrier behind your cement board, you've come to the right place. We've done our research, and here's what we have found.

You must consider installing a vapor barrier behind your cement board to prevent moisture from accumulating on your wall, which can cause mold and mildew. If your cement board is already waterproof, you don't have to install a vapor barrier anymore. 

It can further trap moisture if you have a double vapor barrier.

In this article, we will discuss if it is a must to attach a vapor barrier behind your cement board, how to apply it, and what happens if you don't have a vapor barrier. Keep reading to learn these exciting answers.

Is Having Vapor Barrier Behind The Cement Board Necessary?

The walls of the frame house are sheathed with a vapor barrier membrane

Cement boards are known to support your internal and external walls, which can further strengthen the underlying framework. Hence, it is always advisable to use this in place of drywall when constructing new homes. 

Cement boards are frequently utilized mainly due to their resilience and strength, which can effectively withstand various stresses and maintain their shape.

However, its material typically retains moisture, keeping it constantly damp. You can always use vapor barriers behind your cement boards which are breathable materials that can keep moisture out of your cement boards.

Keep in mind that your wall must only have one vapor barrier layer. There are cement boards that are already equipped with waterproofing material. Thus, if you add a vapor barrier behind it, it will just trap the moisture.

How To Install A Vapor Barrier Behind A Cement Board

Unfinished basement with wood framing and insulated walls, Do You Need A Vapor Barrier Behind Cement Board?

Your goal is to keep moisture away from your cement board. In this case, you may need vapor barriers, which are an essential kind of waterproofing.

When you install it correctly, it will surely stop any moisture from passing through your wall. Here is the step-by-step process on how to properly install your vapor barrier:

1. Clean the Area

Professional cleaning of the premises after renovation with industrial vacuum cleaner

Remove any unnecessary materials present in the area that can be a barrier to you when you attach your vapor barrier. Also, clean the entire room using a vacuum cleaner so no dust may adhere to your vapor barrier.

Click here to see this Eureka vacuum cleaner on Amazon.

2. Get the Proper Measurements

Black Numbers of Measuring Tape

Accurately measure the vapor barrier size you need for your wall using a tape measure. It is also better to extend its measurements.

You can remove the excess just by using a cutter. You may also tape any seams that overlap.

Click here to see this cutter on Amazon.

3. Attach Your Vapor Barrier

Roofing construction A roofing contractor is installing a vapor barrier

Moisture can still pass through your wall, depending on the effectiveness of the application. Position your vapor barrier where it can cover the entire surface. Use a staple gun to attach the vapor barrier. 

Click here to see this staple gun on Amazon.

Make sure to staple them on the borders of wall studs so they won't come off. Take note that every 12 to 18 inches, that's where you must staple another stud.

Tape any holes present in your vapor barrier using duct tape. This action can help stop the vapor from penetrating your cement board. Take your time and get it done correctly.

Click here to see this duct tape on Amazon.

4. Mark Your Cement Boards

Place a mark on your cement boards to determine where to attach the screws.

5. Place Your Cement Boards

Make sure to have accurate measurements of your cement boards on where you will place them. The best way to attach your cement boards is by using screws.

Click here to see this set of screws on Amazon.

Using an electric screwdriver, attach your cement boards directly to the studs so they will not wobble and come off.

Click here to see this Hendoct cordless screwdriver on Amazon.

To make sure, you may also use a stud finder to spot the studs. You may use either a regular stud finder or the magnetic stud finder. Either of the two can still detect studs.

Click here to see this stud scanner on Amazon.

Place your stud finder along the surface and move it horizontally. For the regular stud finder, it will beep if it detects a stud.

On the other hand, your magnetic finder locates the stud if it sticks to the surface when you leave it. This adherence is due to its magnetic capability. It detects the metals behind the wall, which are your nails or screws.

Click here to see this Studbuddy magnetic stud finder on Amazon.

You can place your cement boards horizontally or vertically.

What Happens If You Don't Install A Vapor Barrier?

apartment room with mildew and mold problem on the white wall

Understanding moisture is one of the most crucial components of ensuring that buildings do not prematurely degrade. When moisture penetrates your walls, it may lead to the deterioration of building materials. It can form mold and mildew, causing it to rot.

Also, it can damage your studs and cause the nails to come off. The moisture damage will be evident as rusted-out nails and mold growth.

Using a vapor barrier, you can prevent condensation from developing on the inside surfaces. However, moisture may still enter through vapor barrier holes if you don't attach it correctly. That's why sealing the vapor barrier when there is the presence of holes is always crucial.

This concern also goes the same when you install a shower. Regardless of how airtight you believe your shower to be, water vapor may still enter. Moisture can find its way to enter inside, such as through damaged grout.

Condensation happens whenever warm shower steam comes in contact with the cool bathroom air. You must install a vapor barrier to stop the issues like mold, so that moisture cannot anymore penetrate. 

What Material Is The Best Vapor Barrier?

Vapor barrier walls. Construction work on the insulation of the house

The primary purpose of constructing a vapor barrier is to prevent moisture from entering the inside of your wall.

You can shield your walls against moisture by using a polyethylene vapor barrier behind your cement board. It also prevents corrosion and damage from the sun, dust, and water. It can maintain its characteristics even when exposed to chemicals and aggressive organisms.

Click here to see this polyethylene sheeting on Amazon.

Plastic is one of the most significant materials for water resistance and waterproofing. As a result, your wall is incredibly protected against wetness. Polyethylene plastics are often made of thin, film-like material and are available in various sizes.

Polyethylene plastics are considered impermeable and have a rating of 0.1 perms or less. On the other hand, permeable materials are more porous and have higher permeability.

To install it, you can use a staple gun and staple it to the studs. You may also use tape to seal any holes in your polyethylene vapor barrier.

Additionally, you can use oil-based paints as a vapor barrier. This construction technique can also dry out inner walls against moisture. To accomplish this, use a paintbrush to apply your oil-based paints to the studs.

Click here to see this Rust-Oleum oil-based paint on Amazon.

How Thick Should The Vapor Barrier Be?

The thickness of the plastic sheeting increases with the number of mils. The ideal thickness for your vapor barrier is at least 0.006 inches. This thickness can already be a defense against objects with sharp corners and is great for construction.

You might need an even thicker barrier if you're covering material with sharp angles.

In Closing

Unfinished basement with wood framing and insulated walls

A vapor barrier must be robust to resist moisture. Hence, polyethylene plastic best fits as the vapor barrier to your walls. 

You must install vapor barriers properly to prevent moisture buildup in undesirable places that could damage building materials. A successful moisture barrier requires complete air blockage, increasing the wall's efficiency. Always remember to avoid utilizing two vapor barriers for your cement boards.

Knowing about the appropriate construction of a vapor barrier for your home is beneficial, especially if you want to do it yourself. We hope you found the guide for installing a vapor barrier behind your cement board helpful. Before you leave, we also have other posts that might interest you:

Should I Use A Vapor Barrier In My Garage Walls?

Kerdi Board Vs. Cement Board: Uses, Differences, & Considerations For Your Project

How To Fill Gaps Between Tiles [Using Grout, Caulk, Gap Filling Powder, Or White Cement]

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