Caulking a shower pan is an easy do-it-yourself project that won't take long. You most likely have all the tools which are needed. You must keep the shower pan caulked to prevent water from leaking down the shower walls and under the pan, which can cause water damage.
Step 1 - Remove Old Caulking
Remove all of the old caulking. Most likely there are already places where it has lifted, separated, split along the seam. Starting there, just get a firm grip on it and pull. Continue until all of the old caulk has been removed. If there are stubborn areas or little lines of old caulk, remove them by cutting them lightly along the edge with the box knife, being careful to not scratch your tile.
Step 2 - Clean the Area
Once you have removed the old caulking, mix 1-tablespoon of bleach with 1-cup of hot water. Using the small brush, scrub the area to remove mold that may have formed around the caulking. Open a window and run a fan, as the chlorine odor will be strong.
This step is necessary because the new caulk won't stick to a moldy surface. If the mold is not removed, it will continue to grow. Wipe the area with a clean cloth and allow the area to dry.
Step 3 - Prepare the Caulking Gun
Fill the caulking gun. Remove the end cap and save it. Use the box knife to cut the tip at a small angle. Usually the tips are marked with various lines to cut for the proper angle. Choose the line nearest the tip. You will need to take a long nail and insert it in the tip to puncture the inner seal of the caulk on some tubes of caulking.
Step 4 - Start Caulking
Start in the corner and as compress the trigger on the caulking gun, pull the gun slowly toward you, and leave a small round bead of caulking on the seam line between the wall and the pan. Move the gun continuously until you reach the next corner, then stop. Dip your finger in the dishwashing soap to make it slippery so that the caulk won't stick to your hands.
Lightly drag your finger along the caulking, flattening it and leaving an even ribbon of caulk. The key is to not use too much caulk. If too much caulk builds up on your finger before you get to the corner, stop, wipe it off, add more soap, and start where you left off. Continue this way around your shower pan until you are finished.
Touch up uneven areas and allow the entire surface to dry for 24 hours. Replace the cap on the caulk or insert the nail into the tip to keep it open and free of hardening caulk.