When you are remodeling a bathroom, there are many steps that you must follow to make sure it is done right.
One of these steps is to make sure that the fixtures you install stay in place for years to come.
For many people, it can be a bit confusing as to whether or not you need to set the tub in place or if its weight will keep it in place.
If you are wondering whether or not you need mortar under a tub, we have all the information you need.
Do I Need Mortar Under Tub?
It is generally recommended to put mortar under a tub as the mortar will help make sure the tub stays level and square for years to come.
Mortar is not challenging to use, and you can pretty easily add this to your installation process when you put in a new tub.
This is something that even a DIY homeowner can do when they are remodeling their bathroom.
There are a few steps you should follow when you put mortar under your tub.
We will go through the simple steps involved in this process so you can get your tub properly installed today.
Steps to Install Mortar Under a Tub
The following steps will give you a basic idea as to how to install mortar under your tub.
It is best to have a friend or family member available to help you with this project.
Since the tub itself has a bit of weight to it, you won’t want to hurt yourself trying to lift and move it into position.
Step 1: Gather Supplies
There are a few things you will need to put together before starting this process.
You are going to need a floor primer to help seal the subfloor before placing the mortar directly on top of it.
You won’t need a large can of this as the area under the tub is quite small.
In addition to the primer, you will need supplies to paint the primer on.
Next, you will need a pencil to mark the shape of the tub.
It’s essential to purchase a thin-set mortar or leveling compound to put down under the tub.
For this project, you will need a five-gallon bucket and also a trowel to mix up the mortar.
As always, you will want to make sure that your finished product is level, so a level is another good tool to have.
You will likely have most of these things around if you are in the middle of a bathroom remodel.
- Five-gallon bucket
- Floor primer
- Thin-set mortar or leveling compound
- A friend or helper
Step 2: Level and Prime Floor
Before putting down the mortar, you are going to want to level the subfloor.
Make sure there are no obvious or glaring issues on the subfloor.
Once you have done this, you will cut the hole for the drain which will line up with the bathtub’s drain.
The subfloor is going to need to be primed.
This priming should be done because it will help with potential moisture issues in the future.
Using a proper floor primer ensures that this paint is the proper formula for keeping the area under the tub dry and stable for years to come.
Make sure that this floor primer is completely dry before you move forward with any other steps.
Step 3: Trace Tub
The next step requires that you put your tub on the floor where you are going to want it to be when the installation is finished.
When the tub is in place, take a pencil and trace around the outside of it.
This is going to help you learn where to put the thin-set mortar without the tub in place.
If you want to try and just measure the tub and draw out where it will be, that is fine.
We like to do it by tracing the outside of the tub so that you get a very accurate representation of where the tub is going to be.
Step 4: Mix Thin-Set
Next, you will take your five-gallon bucket and start to mix up your thin-set.
You can read the back of the package of thin-set to find the exact formula mixture of thin-set to water.
Overall, you will want to fill about one-third of your bucket with the thin-set and then mix from there.
That will allow you enough to set the bottom of the tub correctly.
The consistency of the mortar should be stiff enough that it can stand up at a peak.
The peak will fall down after you let it go, but it should still have enough stiffness and substance to it that it can, in no way, be considered runny.
Once your thin-set is mixed, you are going to want to start working quickly to get it put down.
The mortar takes some time to set, but you still don’t want to drag your feet in this process and end up losing the consistency that you have created.
Step 5: Spread Mortar
Now you will take your trowel and start placing the mortar in small piles around the floor where the new tub will be.
You do not need to spread this mortar out and lay a completely flat floor for the tub to go on.
Instead, you are going to want to leave it in small piles and have the tub compress it when you put it into place.
We recommend the piles to be about two inches high.
They should also be about four to six inches in diameter.
Make three rows of three piles that will sort of frame the bottom area of the tub.
If you are putting in a very large tub, you can think about putting 12 piles in place.
Step 6: Set Tub in Place
Next, you will set the tub in place.
You are going to want to do this while the piles are wet.
If your piles start to dry, they are not going to be as receptive to the tub, and they will end up causing you to have a hard time getting things level.
Place the tub down carefully and evenly so that it covers all of the piles of mortar that you just put in place.
The tub should be close to level as soon as you set it in place.
By setting the piles of mortar as opposed to spreading them around, the tub does a great job of leveling itself.
Next, you will take a level and make sure that the tub is, in fact, level.
An expert tip that we have used is to put the level on the top of the tub when you are checking it.
If you place the level on the bottom of the tub, you will not always get an accurate measurement.
Tubs are designed to help water flow out and drain, so they are not always level.
Make sure the tub is level by measuring the top part, not the bottom of the drain.
Keep in mind that the thin-set mortar is going to need time to dry.
You cannot start to work on the other parts of your tub installation before the thin-set has had time to dry.
Doing so could cause the tub to move and end up causing you issues down the road.
Simply get the tub level and then leave it alone until everything is dry and the mortar is set in place.
How Long Does it Take for Mortar Under a Bathtub to Dry?
The time it takes for the mortar to dry is going to depend entirely on the type of mortar you have purchased and how thickly you put it on.
Traditional mortar is going to take twelve hours or so to set.
If you get a quick-set version, it could be as quick as half an hour.
Most people use the traditional mortar as this is not one of those quick-fix-type projects.
If you are working on replacing mortar under a bathtub, you are probably in the middle of a reasonably sized bathroom remodel.
Can I Use Expanding Foam Under a Bathtub?
Some people like to use expanding foam under a bathtub because of its properties for insulating the water.
With the proper insulation, your tub water will stay warmer, and you may spend a bit less on heating the water up over time.
The problem with the expanding foam is that if you don’t use it properly, it can cause issues for a new tub.
The foam is also not going to lock the tub properly in place the way it would be with the mortar.
You can use some expanding foam if your tub’s design allows for it, however, the mortar is still an important part of this process that needs to be completed.
How Do You Level the Bathtub?
Once your mortar is in place, you will want to make sure that it is completely level.
For those who have dealt with quite a bit of home improvement work, you may know this process well.
Leveling the bathtub is done best by using small shims.
We like to use metal shims when working with a bathtub because of the water’s weight, which can wear down the wood ones over time.
Leveling a bathtub should just take a bit of maneuvering as long as the floor below the tub was level to begin with.
Always make sure that the tub is completely level before moving on to any other steps.
How Many Bags of Mortar Do I Need for a Tub?
For most residential bathtubs, one bag of mortar is going to be enough.
The bag should be about 55 pounds, and you will probably end up having some left over.
If you are putting in a very large tub, it may require a bit more.
Luckily, a bag of mortar is not an expensive thing to purchase.
You will save quite a bit of money completing this project on your own as opposed to having someone do it for you.
Hopefully, you now see that the bathtub will hold up best in the long term with mortar under it.
Although bathtubs are quite heavy and rarely move around independently, they will slide and shift if the mortar is not placed underneath.
This process is relatively straightforward, and the labor can be done within a matter of minutes.
The most important thing is to make sure that the tub is entirely level and the mortar is dry before moving on to the next steps.
If you try and install the drain or start working on tile work around the tub, you may move it a bit and lose the angles that you worked so hard to obtain.