Can you install a bathtub without mortar? While it is possible to install a tub without using mortar, it might not be recommended depending on the bathtub type. 

A better question is: should you? In many cases, mortar is an essential part of the process.

Mortar is typically used to support the tub and keep it from moving. 

Your bathtub model should come with a manual that has specific installation instructions. 

  • What does the manual say about supports?
  • Does your tub have decorative feet or a standard base? 
  • Is there any flex on the bottom?

Information about your tub will determine whether or not you need mortar.

Why Is Mortar Used Underneath Bathtubs?

Mortar is typically used when a bathtub is particularly heavy or supporting a large amount of weight. While mortar isn’t used for every bathtub model, it can be a vital way of leveling and stabilizing your tub.

When the bed of mortar is fresh, you can adjust your tub’s level by pressing it deeper into the bed. This allows you to set the model at precisely the right angle for optimum drainage.

Once the mortar dries, it locks the corners of the tub into place. The tub won’t move when you shift your weight, and you’ll also have support while you sit inside.

This support can improve the insulation and prevent flexing, which is when the floor of the tub warps downward.

Another important note is that a mortar bed can help prevent damage. If your bathtub is made from fiberglass or vinyl, these materials might crack and dry as time goes on.

After years of being stressed under the weight, they become damaged. The support from stabilizing mortar helps prevent this.

A mortar bed isn’t always easy to lay, so you might want to skip it if you’re DIYing your bathtub. In fact, you might have heard your plumber say that they don’t prefer mortar beds.

However, stabilizing your bathtub properly will have important benefits down the line.

What Are The Risks Of Not Using Mortar Under The Bathtub?

There are several potential risks that you undertake when you don’t use mortar during your installation. You’ll need to mitigate these risks and double-check in your owner’s manual that the tub is safe.

These are some of the biggest areas of concern:

  • The bathtub will not be held stably in place, so it might move as you do.
  • The bottom of the tub will “flex” without support, leading to warping and bending.
  • The tub will not be installed level — though you can avoid this if you use shims instead of mortar for leveling.
  • Fiberglass and vinyl materials will start breaking down in about a decade because of the extra stress on them.
  • The floor below the tub will become damaged by the moisture or the weight of the feet.

Basically, if you want extra stability and durability, you’ll want to follow this crucial step. Failing to do so might cause your bathtub or floor to become damaged.

If a tub is small, you might use alternative options to stabilize it. For example, some people use wood paneling or gypsum plaster.

These materials need to be cut to the exact shape of the tub, though. Mortar, on the other hand, can be manipulated into the perfect shape until it dries.

It’s Often Best To Use Mortar For Your Bathtub Installation

With a DIY bathtub installation, you probably want things to be as easy as possible. You might wonder whether mortar and concrete are really the best options for your bathtub.

Ultimately, mortar is an important part of the installation process.

The owner’s manual for your tub should have installation instructions. Does it tell you to set the tub in mortar? If so, you should follow those directions.

Keep in mind that a mortar bed might obscure the legs of a tub. If your tub has decorative legs, you may need to come up with a creative solution.

There are occasional cases in which a tub might not need mortar support. Tubs mounted on the floor don’t tend to need it, nor do very stiff tubs.

You might also use materials like gypsum plaster instead of mortar.