This Instructable gives directions for how to fix a crack in a Jacuzzi jetted bathtub caused by having no support under the tub. The person who installed this bathtub left about a 1 inch area underneath the tub that had no support (e.g. an air pocket). Shown here are steps on how to deal with that air pocket and make the bathtub look brand new. The cost for this repair was about $45. Enjoy.

Step 1: The Crack

This crack was caused by stepping into the bathtub where there was an air pocket. You can see the crack in these images.

Step 2: Drilling the Tub

To gain access to the air pocket you will have to drill a hole in the tub floor. Use a 3/8 inch drill bit.

Step 3: Filling the Air Pocket

Use a foam insulation. I used Great Stuff for gaps greater than 1 inch. Practice applying the foam first on a piece of scrap wood to get a feel for it. Insert the application tube into the air pocket and spray the foam until it fills the entire air pocket. Some foam will expand out of the hole. Wipe this excess foam away every 2 to 3 minutes until it stops expanding.