Can anyone recommend a sealant to paint wall with after stripping current wallpaper to prevent mildew reappearing after repapering?
Need to solve the cause of the mildew, otherwise it will return,could be cause several things leaks,poor ventilation,etc.
You have relsove the problem, then treating the wall achieves nothing as the mildew would form on the paper regardless of wall treatment, if the cause is still present.
If any leaking/ventilation issues have been sorted you shouldn't see it come back. If they haven't, you will. Assuming the cause of the mildew has been resolved then you could add a bit of fungicidal wash to your sugar soap solution when you've done the strip. That will make sure you've killed any spores. It would be wise to do all surfaces, including skirting, architrave etcetera. Flooring too ideally.
Someone on this forum, could have been Astramax, uses Sodium Percarbonate,(safer than bleach) which is very good for mildew, but you do need to rinse the surfaces afterwards.
External wall, solid construction maybe so wall is cold, leading to condensation and mould forming ? May be worth taking a look at Wallrock Thermal Liner, a good, high tech lining paper to prevent this from happening Seems expensive, then you have to use their specific paste, (expensive)but large roll sizes available and it really does work Once dried out, use heavy lining paper say 1400 grade and it's ready to paint (think Wallrock may suggest using their own lining paper (again expensive) but not sure if this is a sales ploy or not ! Worth reading up on though and considering