How a Hot Tub is Built

How a Hot tub Is Built Overview

Video featuring Hot Spring Spas

Hot tubs are generally built in the following steps. Each manufacturer will have slightly different orders and some have additional steps that are unique to their spa models.

Step #1
Building the Shell of the Spa

What is a Hot Tub shell Made of?

An hot tub shell is made from a single sheet of acrylic material. The acrylic is heated until it almost melts. It will visibly sag in the middle.

It is then placed over a mold for the specific spa model being built. Each spa model will have a different mold. Powerful vacuums help suck out any air trapped between the mold and the acrylic sheet, pulling the acrylic to the mold.

This results in a smooth and perfectly formed shell. After the acrylic shell has cooled and hardened (which takes about 3 minutes after being vacuum formed), it’s reinforced with a combination of resin and fiberglass to give it additional strength and waterproofing.

Some acrylic shells are formed through a variant process where a layer of the polymer acrylonitrile butadiene styrene, also known as ABS, is pre-applied to the acrylic sheet before going into the mold. The resulting hot tub shell is durable, energy efficient, and aesthetically pleasing.

If you own an acrylic hot tub, it will withstand normal wear and tear for many years without showing signs of damage. Acrylic hot tubs are produced in a variety of stunning colors and patterns.

Also, acrylic hot tubs retain their heat very well when insulated with a high-quality material.

Acrylic tubs are more expensive than vinyl or plastic tubs. However, their ability to hold in heat translates to better energy efficiency than other hot tubs. This results in a lower electricity bill needed to keep your water hot and relaxing.

While hot tub shells made of other materials have some advantages, hot tubs with acrylic shells are the ideal choice, for those who value quality, performance, and appearance.

To learn about other hot tub shell types check out this page from hot spring spas.

Steps in making a spa’s shell

1. Acrylic sheet cleaning

• • High pressure air is used to remove any dust or particles clinging to the acrylic sheet before it goes into the oven

2. Cleaning of the vacuum mold

• • The mold is wiped down and any particles that wont wipe off are removed using specialty tape.

Cleaning the acrylic sheet

Cleaning the mold

3. Heating the acrylic sheet

• • The sheet is heated to over 400 degrees for 3-5 minutes depending upon the spa model being produced. 

Heater Panels

Heated Acrylic Sheet

4. Vacuum forming the shell

• • See the Adam Savage’s Video below of a small scale vacuum forming process. Please note that Adam Savage is using different materials and equipment than a spa manufacturer, but the heating and forming processes are the same.
  • For a more in depth look the video below from Master Spas shows the spa vacuum forming process.

Small scale example of Vacuum Forming

Hot Tub Vacuum Forming (Ft. Master Spas)

5. Reinforcing the shell – AKA Lamination

• • Shells that are not pre-treated with ABS go through a process called lamination. This two step process waterproofs the shell and  adds structural stability.
    • Lamination – Step 1: a device called a chop gun mixes vinyl-esther resin with fiberglass for enhanced waterproofing.
    • Lamination – Step 2:  Polyester resin is mixed with fiberglass,  again with a chop gun, and added to the bottom of the shell to add strength to the shell.
    • After both materials are added to the shell the fiberglass mixture is rolled smooth getting rid of air pockets that will weaken the shell and cause potential leak risks. 

6. Cutting holes for jets and electronics

• • Holes are then hand cut out of the shell to allow for jets, lights, filters, air valves, and top side control panel.

Step #2
Adding the spa’s frame, plumbing, insulation, & electronics

7. Adding plumbing, pumps, & Insulation

• • Depending on the model being built the number of pumps and jets will vary.
  • A Hot Tub’s insulation will vary by manufacturer. Some prefer full foam insulation. Others will wrap the interior of the spa with a special type of insulation.

8. Adding Electronics, Heaters, & Controls
   

• • Topside controls, Heater, Temperature Sensors, Main Control Board, Speakers, Bluetooth, WiFi, LED Lights.
  • Electronic options vary based on spa models. All spas come with a minimum of a heater, main board, temperature sensors and top side controls.

Step #3
Closing up the Spa & Final Testing

9. Installing the cabinet panels (Skirting)

• • Cabinet panels or skirting are the outside of the spa and can come in a variety of colors or even a false stone finish depending upon the manufacturer’s options. These panels help keep the heat in, the insects and bugs out, and make your spa look great. 

10. Final inspections and testing

The final inspection is an important phase of building a spa as it checks to make sure there are no leaks, deformities, electrical issues, etc. before being drained and shipped out of the factory to later end up at your home. If any issues are found they are repaired and the spa is retested until it is fully ready to be enjoyed in your back yard.