New surfaces:
Make sure that the surface is free from humidity, remove any efflorescence by brushing.
Old surfaces:
Remove any peeling parts, level out any irregularities, seal any cracks.
Old paintings:
Remove by brushing peeling paints and other contaminants. In case of mould, do a preventive wash with a suitable restorer before brushing.
Wait at least 4 days from the application of the product to fill the tub or swimming pool with water.