My name is Jonathan Horton and I run JHDS plumbing
Below in this article I will be running through one of the three most common reasons for leaks in the bathroom and ways in which to deal with it, hopefully saving the reader time and money. Before checking or sorting out any of the problems below, take off your panel alongside of bath or under your shower and have a good look with a torch and carry out a few tests like running the shower over the rims of the bath where it meets the wall or spray the shower all-round the enclosure. Then with a combination of a torch and using your hands check for drips and wet patches which will give you some inclination of where the leak is residing.
One of the most common and easily repairable problems is mouldy and cracked damaged grout around your tiles. The ways to check are simply to inspect it thoroughly for hair line cracks, gaps or pin holes. If you manage to eliminate other causes like old silicone sealant and think cracked grouting is the cause then here is how to repair it.
Nip down to local DIY store and pick up some anti-mould-grout of the specified colour to match your bathroom, a grout float, mixing tub and one of the various tools you could use to mix the stuff up.
Before you can think about applying the new grout you have to go about cutting out the bad stuff. To do this I use a 'Bosch 180 E multi tool' with grouting blade. Other cutters like 'Dremmel' also work well but I would strongly advise against a grinder as you l end up losing half the tiles along with the grout. Run the multi cutter along the lines cutting down around 50 percent of infected grout until you see the whiteness of the old grout. You could cut it all of the way out but personally once the blackness has gone and the whites back I personally think its fine to add new better grout too before finishing off with a spray grout sealer. After cutting out all the grout, wipe down with a sponge or wet cloth to remove any dust or debris before applying new grout. Pour some of grout powder into a mixing pot then add TINY amounts of water until it forms a kind of thick paste so that when stuck to trowel should stick when turned upside down. Now you are ready to re grout the affected area. Take your trowel and add a lump of grout onto end of rubber grout float. Start by pushing the mixture into the gaps moving in a diagonal fashion if possible, the remnants that's not made it into the gaps you can sweep up with the float as you go. After fully filling all the gaps, try smoothing off the lines by licking your finger and running it down and across the joins. Now you need to leave to dry for 5 -10 minutes before using your sponge, running at a diagonal angle to wipe down the grout and clean up the joins. After this leave until next day to dry and finish off with a grout spray sealer. A can of spray sealer can be bought from 'Topps tiles' for around 16. To apply just spray over the grout lines and leave to dry, this forms an extra invisible barrier to stop it ever happening again.