Plaster of Paris, also known as Calcium Sulphate Hemihydrate, is a quick-setting plaster made from gypsum. It was named Plaster of Paris because of the wide availability of gypsum in Paris.
This plaster hardens when it’s wet, and it does not shrink or crack once it dries. Plaster of Paris is common in construction projects and medicine because it creates plaster casts for orthopedic care. In today’s article, I will focus more on the uses of Plaster of Paris in the shower, specifically under the tub.
A shaky or squeaky tub is something we have all experienced, whether it’s at a hotel or a friend’s home. The main reason why tubs shake is if there is no bed to offer support.
A bed under a tub doesn’t just offer support. It also prolongs the life of the tub. If you are building a tub and wondering whether you can use Plaster of Paris. Keep on reading to learn more.
Can You Use Plaster of Paris Under a Tub?
Yes, you can use plaster of Paris under a tub. It will offer the needed support and stability, thus preventing the flexing of the tub.
Unlike most products you can use to fill the void between the floor and tub, Plaster of Paris is inexpensive and readily available.
However, there are also a couple of concerns you need to be aware of before you can start applying Plaster of Paris under your tub.
Why Do Tubs Need Support?
Even before we discuss the use of Paris’s plaster under tubs, we must mention why tubs often need support. Many people don’t know this, but tubs don’t have a flat surface.
All tubs are inclined at a specific elevation. The purpose of this inclination is to ensure water drains out effortlessly.
Due to the above reason, tubs need support at the bottom, and that’s where Plaster of Paris comes in handy. It will hold the tub and prevent flexing and squeaking.
Besides Plaster of Paris, a wide range of products can be used to fill this void. We will compare these alternatives later on.
How Much Plaster of Paris is Needed to Support a Tub?
When using Plaster of Paris as support for your tub, you need to ensure you apply an adequate amount that won’t leave a void.
The amount to be used depends on the size of your tub. Most tubs measure from 60 to 72 inches long and 30 to 40 inches wide.
Therefore, a 25kg bag should be enough to complete the job. If some are left behind, you can always store them for future use.
As mentioned earlier, Plaster of Paris has a wide array of uses. You can use it to decorate your ceiling and much more.
How to Apply Plaster of Paris Under a Tub?
Step 1 – Prepare the surrounding deck. If you are installing a tub, there is a good chance you will install tiles and other materials.
Setting Plaster of Paris bed needs to be the last option because once you do, you will need to drop the tub inside the bed.
Step 2 – Install a metal lath over the subfloor. The reason I am advising you to use a metal lath over the subfloor is that Plaster of Paris is very picky about what it will stick to.
If the subfloor is made of wood, some adhesion problems may occur. The metal lath ensures the Plaster of Paris bonds better to your subfloor.
Step 3 – Mix Plaster of Paris with water. The recommended ratio is two parts Plaster of Paris should be mixed with one part of water. Mix the two ingredients until you achieve a thick consistency.
Step 4 – This is where things get real. Plaster of Paris sets quickly. So, don’t waste time and create a bed according to the required measurements. It would be best if you were quick.
Step 5 – Drop in the bathtub and let the Plaster or Paris cure. Please give it a couple of days before using the tub.
Concerns for Using Plaster of Paris Under Bathtub
From the above, it’s clear that Plaster of Paris can offer your tub the stability it needs. However, are there any concerns associated with using this type of plaster under the tub? Well, you need to take note of a couple of things.
1. Plaster of Paris has a Quick Setting Time
The first issue with using Plaster of Paris under your tub is its quick setting time. That means you will have to be fast, or the prepared plaster will start to dry even before you can spread it.
If you are a newbie or usually take your time installing plaster, this option may not be suitable for you. Before you choose Plaster of Paris, you need to know about its quick setting time and evaluate whether you are comfortable with it.
2. Hard to Install on an Already Fixed Tub
If you are building a shower and want to create a support base, then laying Plaster of Paris will be a breeze. But getting Plaster of Paris inside that void will be super difficult if the tub is already installed.
If you are in such a scenario, I recommend expanding foam because it is much easier to use than Plaster of Paris.
3. It May Break Up Over Time
Even though Plaster of Paris has its highlights, such as being inexpensive, lightweight, and readily available, there are some potential drawbacks.
One of them is that it breaks up over time. Plaster of Paris will offer a solid foundation for your bathtub for a while. However, it will crack eventually, especially if you have installed it over the wrong surface.
This, however, doesn’t have to be a big cause for concern. After all, even if you use other alternatives, none of them will last forever.
Do You Need Plaster of Paris for Self-Supporting Tubs?
No. As building materials improve, so should we. Plaster of Paris is a great product. But it won’t be necessary if you had a self-supporting tub in the first place.
Such tabs are covered in fiberglass, and this minimizes flexing. Therefore, if you are yet to buy a tub, look at the self-supporting options. These will minimize the need for using Plaster of Paris.
Plaster of Paris Alternatives
Plaster of Paris can act as a bed for your tub and prevent flexing. But as we have seen, it has some drawbacks. The good news is that you can use a couple of alternatives. Some of them include the following;
• You can build a stable frame. You can build a stable frame on the bottom and sides if you want a long-term solution and no shortcuts. You can create a DIY frame or ask a plumber to build one for you.
• You can use thinset mortar. If you have an issue with how Plaster of Paris sets quickly, you can always use thinset mortar. Mortar takes much longer to cure, giving you a longer working time. Besides that, mortar conforms well to the base of the tub.
• Another alternative to Plaster of Paris that is easier to use is spray foam. Spray foam doesn’t just support the tub. It also offers insulation. Spray foam can also be used on tubs that have already been fitted. Use foam sparingly because it can over-expand and lift the tub out of position.
• Lastly, you can use plywood. Measure and cut a piece of plywood that supports the base of the tub. The problem with plywood is that it won’t adhere to the tub. There may be some occasional squeaking.