Weed seeds and moss algal spores can still fall onto your paving and germinate, but the surface is unattractive for them as it is not longer damp and porous, and so they are less likely to germinate. Equally, should they germinate there is less likelihood of their roots or filaments to be able to get a foothold on the sealed paving. In any event, weeds moss and algae should now be easy to rinse or brush off.
