Jacuzzi Tub – Mortar or Construction Adhesive Base

Should Mortar or Construction Adhesive be used for Jacuzzi Tub Base

By Mark J. Donovan

Jacuzzi tubs have grown in popularity over the years. The pressure jets associated with Jacuzzi tubs provide high velocity streams of heated water and air to the occupants of the tub that provide for a comforting and relaxing bath experience. As a result of their popularity many do it yourself homeowners are installing their own Jacuzzi tubs nowadays. During the installation process the question often arises on whether or not a mortar or construction adhesive should be used in the base.

The short answer is a mortar base is preferred, however always defer to the Jacuzzi tub manufacturer’s directions.

So why is a mortar base preferred over using construction adhesive?

The answer is quite simple. Jacuzzis tubs are made out of fiberglass materials that are fairly rigid, but do flex to some degree. This flexing causes stresses on the Jacuzzi tub as well as creates squeaks. By resting the Jacuzzi tub in a bed of mortar any gaps, or voids, between the subfloor and the base of the Jacuzzi tub are filled. By filling the voids, the Jacuzzi tub is better supported and is less apt for flexing or squeaking.

On the other hand, simply applying a construction adhesive on the bottom surfaces of the support spacer blocks will prevent lateral movement of the tub, but does nothing in regards to offering additional support.

Installing Jacuzzi Tub into a Mortar Bed

To install a Jacuzzi tub into a mortar bed first construct the 2×4 or 2×6 framing for setting the tub into. Make sure in the process of framing the Jacuzzi tub walls to specify an access location for the Jacuzzi tub’s electrical wiring and pump.

Now, pour 2 inches of mortar, such as Quickrete Sand topping mix mortar, into the base of the Jacuzzi tub framed area. Make sure to leave voids in the mortar bed for the Jacuzzi tub pump and support legs. Read the Jacuzzi tub manufacturer’s directions to determine where the mortar voids should be located.

Next, immediately drape a layer of polyethylene plastic over the soft mortar bed.

Then immediately apply construction adhesive to the bottom of the Jacuzzi tub support spacer blocks.

Next, apply silicone adhesive around the top perimeter edge of the framed in area to create a water tight seal with the bottom edge flange of the Jacuzzi tub.

Now place the Jacuzzi tub into the framed in area. Make sure the Jacuzzi tub sits properly on its support spacer blocks.

Connect the electrical wiring and plumbing up to the Jacuzzi tub. You may need to have an electrical inspection completed by the building inspector at this point.

Then install insulation around the Jacuzzi tub area to help retain heat.

Bathroom Remodeling Bid Sheet

Finally install greenboard or cement backerboard to the outside surface areas of the Jacuzzi tub area. Note that if you plan to tile around the Jacuzzi tub it is important to use a cement backerboard as it is meant for wet environments. Greenboard will not hold up to repeated moisture exposure.

For help on your bathroom remodeling project, see my Bathroom Remodeling Bid Sheet. The Bathroom Remodeling Bid Sheet provides a request for quote checklist section that you can provide to prospective bathroom remodeling contractors. It also includes a comprehensive bathroom remodeling cost breakdown table, in Microsoft Excel format, that allows the contractor to include his projected remodeling costs for every phase of the project.

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