New answers tagged caulk
Backer rod should be compressed in a joint. If it doesn't stay in the joint on it's own, then you need to get a wider piece. They come in varying diameters and you should choose one slightly wider than your gap.
As already stated, this is a problem with the mould and you cannot really correct it. The only thing that i would try, is to chip away the existing silicon and cement around the corners of the ledge and then try to get something which you could use to pry the ledge upwards ever so slightly. What I would use is some expanding foam, you will be surprised ...
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