I am going to fit seagull spikes to my ridge tiles and chimney once the current family have disappeared. I've put up with them for many years but now they are dropping shellfish onto my flat roof from a height to break them open, enough is enough. The recommended adhesive for these is silicone, applied to a cleaned surface which is no problem. However, would I be advised to seal the surface of the ridge tiles and brick with something like PVA before using silicone?