Look at repaircare if you want a better solution. They have a lot of videos showing the process. I get through quite a bit of it repairing these kinds of problems but I have to really like someone to want to do it these days. Working on your knees in the damp is a painful experience.
I filled my own with some epoxy resin cement I had left over in a tin and it's worked a treat for years.
They have started doing Repair Care at Crown Decorating Centres. Otherwise I think Sealants Online is the go to online place recommended upthread, who do the kits for a decent price.
Look at repaircare if you want a better solution. They have a lot of videos showing the process. I get through quite a bit of it repairing these kinds of problems but I have to really like someone to want to do it these days. Working on your knees in the damp is a painful experience.
I filled my own with some epoxy resin cement I had left over in a tin and it's worked a treat for years.