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What Kind of Mortar to Use Under the Bathtub? (Explained)

There are four different types of mortar available on the market. They all have different purposes, and you can use them in different parts of your building or house. Some are good for the interior design; others are great for the exterior joining or piping.

Since mortar is used to join and give an excellent finish to the tiles, walls, and pipes, you can also use it under the bathtub. Bathtubs are specially designed to place in the washroom, and you need to secure them through the mortars or cement mixture.

What kind of mortar to use under the bathtub?

You can use the Regular thin-set mortar under the bathtub. It is an adhesive mortar that will firmly attach to the bathtubs. Thinset mortar is made with adhesive cement, water, sand, and other ingredients. You don’t need to make any manual mortar for your bathtub.

Not all mortars have the same ingredients and same workability. Let’s find out what mortars you can use for bathtubs.

Ready-made Mortar:

Four ready-made types of mortar you can buy from the local cement shop. They are all good for the bathtubs.

Among them, the regular thin-set mortar will be a great fit. It has adhesive ingredients that will stick to the bathtub securely.

Therefore, your priority should be the thin-set mortar. Then you can consider buying the others. Before applying the ready-made mortar, you must prepare the tiles and floor; otherwise, it will be messy and won’t work smoothly.

Home-Made Mortar:

You can also create the mortar at home. You need cement, sand, and water to make it. Here, you can use the adhesive cement to make the mortar perfect for your bathtub.

Add all the ingredients one by one and mix properly. When you add the water, make sure it is minimal. Don’t put excessive moisture into the mixture.

After successfully mixing them all, you can apply them on the floor or the bathroom. Then place the bathtub there.

Mortar vs adhesive for bathtub, which one is better?

You can use both the mortar and adhesive under your bathtub; they both are fine and will firmly stick to the bathtub. 

Mortar is better than adhesive construction. Mortar has cement, sand, and water that work as a natural adhesive material under the bathtub.


The thin-set premixed mortar is better than any other adhesive material. It will stick to the bathtub once it is dry. The premixed thin-set mortar has pretty much every ingredient you will need to place your bathtub securely.

Among them, the cement works like an adhesive material; therefore, you don’t need to use any additional adhesive material under the bathtub.

Mortar can be made at home. If you want to make a budget-friendly mortar, you can buy cement and sand. Put them on the floor and mix them properly. Add some water then you are done making the mortar within a small budget.


Adhesive material is costly, and you cannot rely on it for a long time. If you buy a modern bathtub that doesn’t require any extra mortar to place it, you can use the direct adhesive material to install it in your bathroom.

Most modern bathtubs are easy to install, and they will firmly attach to the floor.

When you have a typical bathtub that needs to have mortar to stick to the tiles, you cannot rely on the adhesive material. If you buy the adhesive construction, it will cost you more. Here the mortar will give you the best solution.

Why put mortar under the tub?

You should put mortar under the tub to make it secure and stick to the tiles as well. More reasons are there.

Stick to the tiles:

The tub needs to stick to the tiles firmly. Otherwise, it will move, and you cannot enjoy taking a shower in it.

Using the tub without putting any mortar under it will be a risky factor. Here the mortar will help the tub to stick to the tiles.

Prevent Moving:

Bathtub has a flat surface. It will move if you don’t use any mortar under it. Besides, the bathtub will not be fixed in a specific bathroom space. To stop or prevent the moving, you should use the mortar under it.

Support the weight:

Bathtub has a massive weight. It will be difficult for the tiles and floor to support the weight properly. 

Therefore, you should use the mortar to support the bathtub’s weight. The mortar will also keep the tiles and floors secure and hold absolute pressure.

Do you need the mortar bed under all bathtubs?

Most bathtubs need the mortar bed under them. It will secure the placement and protect the plastic-made part. Only the modern and self-placed bathtubs will not require any mortar bed.

Acrylic bathtub:

You need the mortar bed under the acrylic bathtub. Here the mortar will fix it and help to stick to the tiles and will not move anywhere.

If you don’t use the mortar under your acrylic bathtub, it will be a mess, and the bathtub may move.

Fiberglass bathtub:

If you have a big fiberglass bathtub, you need the mortar bed under the tub for making it secure and stick to the tiles and floors. Moreover, the mortar will also support the heavyweight of the bathtub.

These are the most common reasons you should use the mortar under the fiberglass bathtub.

Cast iron bathtub:

You don’t need to put any extra mortar under the cast iron bathtub. It will stick to the floors and tiles.

However, the cast iron bathtub only requires the thin-set mortar under it. You can place the thin-set mortar and set the cast iron on it.

How many bags of mortar do you need for a bathtub?

Two bags of mortar will be enough for a single bathtub. You can also place the bathtub on one bag of mortar. Using the 55lb mortar bag for a single bathtub will be better. But two bags are for the big bathtub and safe use.

Typically the weight capacity and the weight of the bathtub will determine how many bags you will need for the bathtub. If you have large bathtubs and more weight, you should go for the two bags of mortar.

If you want to make the mortar at home, you can follow the rules of making 55lb mortar. So, make a list of required cement and sand proportions and then buy them.

After that, mix them well and add water. Remember, you need to cover the entire place where the bathtub you want to install.

Can I use expanding foam under the bathtub?

You can use the expanding foam under the bathtub. It will be safe and will support the bathtub weight as well. It will help you reduce the coldness and flex of your newly installed bathtub. Therefore, you need to use the expanding foam carefully.

If you make any mistake in applying the expanding foam under the bathtub, it will create issues for you. You can use the expanding foam along with the mortar slab. It will make the interior stronger and more suitable.

Improper installation of the expanding foam will destroy the mortar slab as well. And your bathtub will lose its stickiness. Therefore, you must apply the foam according to the user manual.

How to put mortar under a bathtub?

To put mortar under a bathtub, you may follow our tips.

Prepare the floor/tiles:

Before applying the mortar or preparing the mortar, you should prepare the floor first.

You should clean the floor and remove the debris from there. Then, make the place even and dry. It will help the mortar to stick to the bathtub surface firmly.

Make the Mortar/ Buy It:

You can buy the thin-set mortar to use under the bathtub, or you can make the mortar at home to save your budget.

You need to buy some cement, sand and use water. Make a mixture and apply it to the prepared floor.

You can make the mixture in the adjacent room of the bathroom. It will be easier to make the mixture and apply it soon.

The layer of Plastic:

It’s time to place a layer of plastic on the mortar to protect the underside of the tub. Then, install the tub on the mortar and let it stick for 72 hours. You should not use the bathtub at this time.

If you use any concrete with the mixture, you need water to make it strong. It will be better to water the entire mortar if you use concrete or stone. After that, wait for three days and let it dry from the inside.

Final thoughts

Regular thinset mortar has all the ingredients you need to install the bathtub. It will securely stick to the bathtub surface. Besides, it is an adhesive mortar. When you install or put the bathtub on the thin-set mortar, it will stick to it and not move anymore. So, you can use the thinset mortar.