Is the tile and grout so damaged that cleaning is no longer an option? What about the drain? What condition are the screws in? Have they started to corrode and become impossible to remove?
Shower floors can present some serious issues that can affect the overall condition, performance, and condition. Knowing your options are important in making a wise decision on whether you are planning to repair or replace your entire shower. As a tile contractor in California, offering options to my customers is important to me. Often the overall condition of the shower is good, it's just the lower section such as shower floor that needs attention.
After inspection, with no signs of leaking at the drain or waterproofing under the tile, suggesting a "tile-over-tile" shower floor is a possible option for the customer to consider. It's important to check the drain for any signs of damage. One common issue are the screws that secure the drain screen plate. It's very easy for those stainless steel screws to corrode and become very stubborn to remove. Stripping the head of the screw is usually a result.
If this is your situation, you will need to use an extraction tool bit to remove that stubborn screw. The extraction bit should fit snugly into the hole that was drilled using a high strength drill bit. You need to go slow with this and try to be as precise as possible. The idea is for the extraction bit to grip firmly into the drilled hole. As you begin to turn the bit counter-clockwise, the edges start to bite into the hole. The more you turn, the tighter the grip, which will hopefully cause the screw to break loose. Take your time and turn very slowly with this.
One tip is to apply a penetrating oil at the threads and let soak for 20 minutes. This can really help with breaking the screw loose without damaging the threads on the drain.
If you are successful with the removal of the damaged screw. Use a tool called a "Tap" with the proper thread pitch and diameter to clean out the threads on the drain. It's also a good idea to coat your new screws with either an anti-corrosion lubricant or oil before re-installation.