L
LesD
I guess by the lack of replies that it was the wrong question to ask you guys and I think I have found the right answer myself.
I removed the rest of the offending bit of tile and replaced it with a thinner properly glazed piece of white tile. As this bit of white tile will be completely behind the upright channel of the bi-fold door frame it won't be seen and being glazed should have a waterproof face too. I have stuck it in with Keraquick and will use the BAL microflex grout and Silicon sealant where appropriate. A picture is attached.
I removed the rest of the offending bit of tile and replaced it with a thinner properly glazed piece of white tile. As this bit of white tile will be completely behind the upright channel of the bi-fold door frame it won't be seen and being glazed should have a waterproof face too. I have stuck it in with Keraquick and will use the BAL microflex grout and Silicon sealant where appropriate. A picture is attached.