Can You Use Structo-Lite Under Tub? (Explained)

Most tubs need a mortar bed for support. Bathtubs are usually heavy and support a lot of weight. Therefore, you need to create a mortar bed underneath to offer support and also promote some insulation.

The best support for a tub is a typical mortar bed. However, there are instances when you may not have some mortar close by. And you may consider using Structo-Lite as an alternative.

There are a lot of conflicting opinions out there regarding the usage of Structo-Lite under a tub. In the article below, we will be exploring whether it’s okay to use Structo-Lite under a tub and any potential drawbacks you need to be aware of.


What is Structo-Lite?

In figuring out whether it’s okay to use Structo-Lite under a bathtub, the first place we should start is by defining what Structo-Lite is.

It is a basecoat gypsum plaster. Structo-Lite is known for its high insulation properties and lightweight. Structo-Lite conforms to various shapes and designs. Therefore, you can use it anywhere.

Structo-Lite is very easy to use. You only need to mix it with water and apply it by hand or machine. As a gypsum plaster, Structo-Lite can be used in ceilings and walls. It offers fire protection and sound isolation.

Is It Okay to Use Structo-Lite Under Tub?

Structo-Lite can be used to support a bathtub. A lot of contractors and DIYourselfers use it as an alternative to mortar. There are a couple of reasons that make Structo-Lite a suitable material to use under a tub;

Structo-Lite is very easy to shape and has a long working life. Therefore, it will be very easy for you to create suitable support under your tub.

This gypsum plaster offers a considerable amount of insulation. Tubs can get pretty hot especially when one is bathing in hot water. Therefore, Structo-Lite’s insulation property is an added advantage.

It is also lightweight and that will ensure the overall weight of the tub and its support doesn’t exert a lot of pressure on the subfloor.

Are There Any Concerns Associated with Using Structo-Lite Under a Tub?

There is one main drawback of using Structo-Lite as a support for your tub. Gypsum plaster doesn’t fair very well in high moisture areas.

Considering that the bathtub is located in an area that’s constantly getting wet, Structo-Lite may not last very long unless it’s properly sealed.

As you consider using Structo-Lite under your bathtub, you need to be aware of this significant drawback.

How Much Structo-Lite is Needed Under a Tub?

If you make up your mind to use Structo-Lite, you need to use the correct amount. An 80-pound bag of Structo-Lite is enough to create a strong support bed for your tub.

You may even not use the entire bag and you can store it for future use. Most of the time, you will use at least half or three-quarters of the entire bag.

When creating a mortar bed using Structo-Lite, please make sure that it is leveled in all directions. A significant area of the tub must touch the Structo-Lite bed. When laying the tub, push it against the Structo-Lite so that it’s firmly supported.

To prepare Structo-Lite for the creation of tub support, you need to mix it with water. The ideal ratio for mixing Structo-Lite with water is to achieve a peanut butter consistency.

You should avoid applying the Structo-Lite when it’s too stiff as that will make it harder for you to push the tub into position.


Is There Anything Else Needed When Creating a Tub Bed Using Structo-Lite?

There is one more thing that comes in handy when using Structo-Lite as a support bed and that is a sheet of plastic.

Most professional installers use a sheet of plastic between the floor and Structo-Lite and between the Structo-Lite and tub.

Here is why a sheet of plastic comes in handy. If you intend to remove the tub in the future, attaching it directly to the mortar can make it difficult to uninstall. But if there is a layer of plastic sandwiching the Structo-Lite, removal will be easy.

Do All Tubs Need a Structo-Lite Bed?

If you have recently bought a new tub, check if it has wood bracing embedded with fiberglass. Such tubs don’t need extra support.

They can do fine on their own. If you are unsure, confirm with the seller whether that tub requires additional support or not.

Modern bathtubs are designed in some ways to be independent and don’t need any extra support. If you own such a bathtub, it would be a complete waste of time for you to create a support bed with Structo-Lite or even mortar.

Certain tubs come with feet. These feet should be glued to the ground and that’s it. There is also no need for a mortar bed.

Do Tub Manufacturers Recommend Structo-Lite as a Support Bed Material?

Tub manufacturers have varying installation requirements. Some may recommend Structo-Lite. Others may be completely against its use underneath a tub.

A pro tip you should follow is to always check the manufacturer’s instructions before using any support bed material.

If a certain manufacturer is against the use of Structo-Lite, refrain from using that material at all costs. Because it may void the warranty. And in case the unexpected happens, no one will offer you compensation.

What Alternatives Can I Use Instead of Structo-Lite Under a Tub?

The best alternative to use instead of Structo-Lite is the plain old-fashioned mortar. A bed made out of mortar creates adequate support while creating some insulation beneath the tub and floor.

Another alternative that people usually use is expanding foam. However, I would advise you to exercise caution when using expanding foam. It may swell too much and interfere with the stability of the tub.

Another alternative that is recommended is ready-mix concrete. This is a cost-effective solution to use to create a support bed.

A layer of tub snugs down easily on the ready-mix concrete. Even when you use ready-mix concrete, you should use a plastic sheet to prevent the tub from adhering to the concrete.

The best material to use for a tub bed should also be approved by the tub manufacturer. Using something that’s not recommended may void the warranty.

How Long Can Structo-Lite Last Under the Tub?

As long as it’s applied correctly, Structo-Lite can last for years. Structo-Lite prevents the flexing of the bathtub while offering support and insulation. As long as it’s not exposed directly to water, the Structo-Lite can last for very long.

Does Structo-Lite Expand When It Cures?

Structo-Lite should not be confused with expanding foam. It dries to a brittle surface that doesn’t expand when it cures. Since Structo-Lite doesn’t expand when it cures, it will not lift the tub when it dries.

Will the Tub Move Around When You Use Structo-Lite?

Structo-Lite dries into a hard surface. When you fit it correctly, the tub will always remain still even when you seat in the tub. Structo-Lite isn’t like expanding foam which flexes when you add weight to the tub.

Also, you don’t want your bathtub to move around after it has been installed. That’s because the flexing may cause it to crack. Expanding foam also makes the tub feel spongy. Such a weak structure is not ideal for a tub.

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