What Should Be Under Tub Should I Have Concrete Under My Bathtub? This Home Is 5 Years Old And I've Had Many Problems With It.?

Should I have concrete under my bathtub? This home is 5 years old and I've had many problems with it.? - what should be under tub

First, my house is on a concrete slab and I am one of the outer wall fiberglass tanks meeting with the ground. A few weeks ago I noticed that the water in my bathtub emerging and thought I realized that the problem was that the flight had a leak. Yesterday I decided to tackle the problem and open to the plaster wall on the other side of the trough. To my horror, was in the plaster mold and an ant along the pipes. Even in my bathtub, there was no concrete. From what I can tell, there was nothing but sand on Earth. This is normal!? I ran the water and could not see the leak is a leak so I'm back to square 1 and will probably open the entire wall. My questions are many, if cXAMPLES under my bathtub? Can not be damaged mold / mildew? Does my warranty cover housing is it? It could be worse?