Can You Use Plaster Of Paris Under Tub? Find Out Here!

No, you should not use plaster of Paris under a tub. Plumbing codes require a solid, stable base for the tub, and plaster of Paris is not suitable for this purpose.

Instead, use a mortar bed or foam padding to properly support the tub. Failure to provide adequate support can lead to structural issues and potentially dangerous situations. Proper installation is crucial to ensure the longevity and functionality of your tub.

When it comes to installing a bathtub, it is important to provide a solid foundation to ensure its stability and longevity. Plaster of Paris, although a versatile material, is not suitable for use under a tub. Plumbing codes require a more stable base, such as a mortar bed or foam padding, to provide proper support. This article will explore why plaster of Paris is not recommended, the potential problems it can cause, and alternative options for supporting a bathtub. By understanding the importance of proper installation and the materials required, you can ensure a safe and durable bathtub installation.

Problems With Using Mortar Under Bathtubs

Problems with Using Mortar Under Bathtubs

When it comes to installing bathtubs, using the right materials is crucial. One common practice is using mortar as the base layer under the tub to provide stability and support. However, this approach is not without its drawbacks. In this article, we will discuss the biggest problems that can arise when using mortar under bathtubs, the associated risks and potential issues, as well as plumbing concerns and their consequences.

Biggest Problems Created When Using Mortar Under Bathtubs

While it may seem like mortar is a safe and reliable choice for supporting a bathtub, there are several significant problems that can arise:

  1. Potential for cracking and shifting: The weight of a filled bathtub, coupled with regular use, can put immense pressure on the mortar. Over time, this pressure can lead to cracking, shifting, and instability.
  2. Difficult repairs: If cracks do occur, repairing the mortar can be a challenging and time-consuming task. It often requires removing the entire bathtub and redoing the mortar layer.
  3. Inadequate water drainage: Mortar is not designed to address water drainage issues. Without proper slope and waterproofing measures, water can seep beneath the tub, leading to leaks, mold growth, and structural damage.

Risks and Potential Issues Associated with Mortar Usage

Using mortar under bathtubs comes with various risks and potential issues that homeowners should be aware of. These include:

  • Incompatibility with certain tub materials: Mortar may not be suitable for all types of bathtub materials, such as fiberglass or acrylic. The rough and rigid surface of mortar can cause damage to these more delicate materials.
  • Limited adjustability: Unlike other alternatives, such as adjustable feet or leveling systems, mortar does not provide the flexibility to fine-tune the bathtub’s position and alignment during installation.
  • Additional weight: Applying a layer of mortar adds extra weight to an already heavy fixture like a bathtub. This can put additional stress on the floor structure, potentially leading to structural problems over time.

Plumbing Concerns and Consequences

Using mortar under bathtubs can have unintended consequences for the plumbing system. Here are some potential issues:

  • Difficulty accessing plumbing components: Once the bathtub is installed on a mortar base, accessing the plumbing components for future repairs or maintenance becomes challenging. This can result in increased costs and inconvenience.
  • Leak risks: The lack of proper waterproofing measures with mortar can contribute to water leaks, which can damage not only the subfloor but also the surrounding areas, requiring costly repairs.
  • Increased installation time and complexity: Installing a bathtub with mortar requires careful planning, precise measurements, and skilled labor. It adds to the overall installation time and complexity, potentially leading to delays and higher costs.

In conclusion, while using mortar under bathtubs may have been a common practice in the past, there are evident problems, risks, and plumbing concerns associated with this approach. It is important to explore alternative methods that provide better stability, adjustability, and long-term reliability for your bathtub installation.

Supported Types Of Bathtubs

When it comes to installing a bathtub, proper support is essential to ensure its stability and longevity. Understanding how different types of bathtubs are supported is crucial for a successful installation. In this article, we will discuss the various methods used to support bathtubs, including the overview of how most bathtubs are supported, support board and attachment to wall studs, and the difference between fiberglass and acrylic tubs.

Overview of how most bathtubs are supported

Most bathtubs are supported using a combination of a support board and attachment to wall studs. The support board acts as a stable base for the bathtub, while the attachment to wall studs provides additional support and prevents the tub from shifting or moving.

Support board and attachment to wall studs

The support board is usually made of plywood or a similar sturdy material. It is cut to fit the dimensions of the bathtub and placed on the floor where the tub will be installed. The board should be level and securely attached to the floor. Once the support board is in place, the tub is positioned on top and secured to the board using screws or other appropriate fasteners.

The next step involves attaching the bathtub to the wall studs. Wall studs are the vertical wood or metal framing members that provide structural support to the walls. The tub is positioned against the wall, ensuring that it is centered and aligned correctly. Screws or brackets are then used to secure the tub to the wall studs, creating a sturdy and stable installation.

Difference between fiberglass and acrylic tubs

It’s important to consider the material of the tub when determining the appropriate support method. Fiberglass and acrylic tubs are two common options, and they have some differences in terms of installation requirements.

Fiberglass tubs are lightweight and flexible, making them easier to maneuver and install. They often come with built-in support features, such as structural ribs or a bottom pan that provides stability. When installing a fiberglass tub, it’s essential to follow the manufacturer’s instructions and use the recommended support methods to ensure a secure installation.

On the other hand, acrylic tubs are denser and more rigid compared to fiberglass. They may require additional support to prevent flexing or cracking. The support board and attachment to wall studs method is suitable for acrylic tubs, but it’s essential to check the manufacturer’s guidelines for any specific support requirements.

In conclusion, understanding the different methods of supporting bathtubs is crucial for a successful installation. By utilizing a support board and securing the tub to wall studs, most bathtubs can be installed securely. Additionally, considering the specific support requirements of fiberglass and acrylic tubs will ensure a stable and long-lasting installation. Proper support not only enhances the functionality of the bathtub but also minimizes the risk of damage or accidents. Remember to consult the manufacturer’s guidelines and seek professional assistance if needed when installing a bathtub.

Alternative Materials For Supporting Tubs

Alternative Materials for Supporting Tubs

Pre-planning and Foundation Materials

When it comes to supporting a tub, there are alternative materials that can be used instead of plaster of Paris. Before starting the installation process, it’s important to pre-plan and consider the foundation materials that will provide the necessary support for your tub.

One common alternative to plaster of Paris is a self-leveling compound. This compound is easy to use and can provide a stable base for your tub. However, it is essential to ensure that the floor is properly prepared before applying the self-leveling compound. Any uneven areas or cracks should be addressed before installation.

In addition to self-leveling compounds, cement boards are another option for supporting tubs. These boards are moisture-resistant and can provide a solid foundation. They are commonly used in wet areas such as bathrooms and can withstand the weight of tubs without any issues.

Setting the Unit and Fastening Techniques

Once you have chosen the foundation material, the next step is to set the tub unit and utilize the appropriate fastening techniques. Whether you are working with a fiberglass or acrylic tub, it’s crucial to follow the manufacturer’s instructions and recommended fastening methods.

Some tubs can be secured directly to the floor using screws or brackets, while others may require additional support through wall studs or surrounding walls. It’s important to ensure that the tub is securely fastened to prevent any movement or instability.

Shimming, Furring, Backing, and Bracing Options

To further enhance the stability and support of your tub, you may consider using shimming, furring, backing, or bracing options. These techniques can help eliminate any gaps or unevenness between the tub and the surrounding walls.

Shimming involves using thin, wedge-shaped materials to fill any gaps and create a level surface. Furring strips can be used to build up the walls and provide additional support for the tub.

Backing and bracing techniques involve installing additional materials behind and around the tub to reinforce its stability. This could include adding plywood or metal brackets to distribute the weight evenly and prevent any movement.

Overall, when it comes to supporting tubs, alternative materials such as self-leveling compounds and cement boards can be used instead of plaster of Paris. By pre-planning, choosing the right foundation materials, and utilizing proper fastening techniques, you can ensure a sturdy and durable installation that will stand the test of time.

Can Plaster Of Paris Be Used Under A Tub?

Exploring the use of plaster of Paris

Plaster of Paris is a common material used for various DIY projects, but can it be effectively used under a tub? Let’s dive into the details and explore the use of plaster of Paris as a base for tub installations.

Porous nature and lack of waterproofing

One of the main concerns with using plaster of Paris under a tub is its porous nature and lack of waterproofing capabilities. Plaster of Paris tends to absorb moisture, making it unsuitable for wet environments such as showers. This could potentially lead to water damage and mold growth over time.

Comparing plaster of Paris to thinset for shower installations

When it comes to shower installations, it is crucial to choose a material that provides proper waterproofing and durability. Thinset, a cement-based adhesive, is commonly used for setting tiles in wet areas such as showers. Compared to plaster of Paris, thinset offers superior waterproofing properties and is specifically designed for high-moisture environments.

While plaster of Paris may be suitable for non-wet areas outside the shower, it is best to dig it out and use thinset as the base material if you’re planning to install a tub in a shower. This ensures that you have a reliable and long-lasting foundation for your tub installation.

Overall, it is important to consider the specific requirements and characteristics of the materials you use when installing a tub. Opting for a suitable product, such as thinset, will help ensure a sturdy and water-resistant installation that can withstand the demands of a shower environment.

Leveling The Floor Under A Bathtub

Importance of Leveling the Floor for Proper Installation

When it comes to installing a bathtub, one crucial step that often gets overlooked is leveling the floor underneath. Properly leveling the floor is essential for a successful and long-lasting installation. Here’s why:

  • Ensures proper weight distribution: If the floor is uneven, the weight of the bathtub may be unevenly distributed, leading to stress on certain areas. This can result in cracks or damage to the tub over time.
  • Prevents water pooling: An uneven floor can cause water to pool around the base of the tub, leading to potential water damage and mold growth. Leveling the floor helps ensure proper drainage and prevents these issues.
  • Creates a stable base: A level floor provides a solid and stable base for the tub. This helps prevent any movement or shifting of the tub, which can lead to leaks or damage to the surrounding tiles.

Techniques for Leveling the Floor Under a Bathtub

Now that we understand the importance of leveling the floor, let’s explore some techniques that can be used to achieve a level base:

  1. Self-leveling compound: Self-leveling compounds are a popular choice for leveling floors under bathtubs. These compounds are easy to use and can correct minor unevenness in the floor surface.
  2. Shims: Shims are thin wedges that can be placed underneath the tub to level it. They are particularly useful for correcting small gaps or unevenness.
  3. Sand mix mortar: Sand mix mortar can be used to create a smooth and level surface for the tub. This method requires careful mixing and application to ensure a level result.
  4. Professional help: For larger or more complex leveling issues, it may be best to seek professional assistance. A contractor or plumber can assess the situation and recommend the best leveling technique for your specific needs.

Remember, each bathroom and tub installation is unique, so it’s important to choose the leveling technique that is most suitable for your specific situation. By taking the time to properly level the floor, you can ensure a stable and secure base for your bathtub, which will contribute to the longevity and functionality of your bathroom.

Frequently Asked Questions Of Can You Use Plaster Of Paris Under Tub

What Do You Put Underneath A Bathtub?

Plaster of Paris is not typically used under a bathtub. It is porous and not waterproof, so it may not provide adequate support. Other materials like mortar or foam are commonly used for stability.

Can You Use Plaster Of Paris In The Shower?

No, it is not recommended to use plaster of Paris in the shower. Plaster of Paris is porous and not waterproof, making it unsuitable for wet environments. It is best to use a waterproof material like thinset for shower installations.

How Do You Level A Floor Under A Bathtub?

To level a floor under a bathtub, you can use plaster of Paris. Before using it, make sure the tub is properly supported and any necessary repairs are done. Spread an even layer of plaster of Paris and level it with a trowel.

Allow it to dry completely before installing the bathtub.


To conclude, using plaster of Paris under a tub has its drawbacks. It is porous and not waterproof, making it unsuitable for shower areas. If used outside the shower, it can be primed to avoid re-wetting during tile setting. However, for optimal results, it is recommended to dig out the plaster and use thinset instead.

Plaster of Paris may not be necessary with newer building materials available. It’s important to prioritize using suitable materials to ensure the longevity and stability of your tub installation.

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