The shower floor will need to be repaired and have all of it’s grout checked and refilled as necessary. Try to match the colour as best as you can. Most older shower floors were grouted in Grey Cement and yellow tilers sand. Which you can get from a local hardware premixed at about 3 to 1.
Mix the sand and cement with water until it becomes gluggy and holds together. Push it into the grout joints with the heel of your hand.
Make sure you are wearing gloves when you apply the premixed grout to the floor. Cement is the main cause of dermatitis. It will leave your hands very dry and cause your skin to crack. This lets in bacteria that will begin the dermatitis. Wash off the excess grout once it has started to dry on the tile face. Leave for a few hours and then use a dry cloth to remove the remaining dust from the grout. Let the floor dry again overnight before you apply the sealer.
Apply the sealer over the grout joints the same way as it is applied to the wall joints. Brush it in well with alternating strokes in either direction.
Remove as much as you can from the surface of the tiles . Use a damp cloth and rinse it often. Try not to remove any sealer from the grout joints.
Once this is done it has to be left to dry for 30 to 40 minutes before you do the final wash and scrub.
Now is a good time to keep looking over the floor tiles to check if any residue is left on them. If there is any use a damp cloth to remove it.
After the floor has dried sufficiently you can begin to clean off the tiles with water and a scourer. Keep rinsing the floor as you go and make sure that the floor looses it slipperiness. Any feeling of slipperiness indicates that there is still some sealer left on the tiles. Just keep cleaning until it feels non slippery or squeaks when you run your finger over it.
You can use your shower immediately after this process.
All that is left is to apply silicon to the corners.