Is it necessary to remove railings and sand dow existing gel coat on a fiberglass deck to apply a new layer? Can we just re-fiberglass on top of what's there after sanding down current surface of the sundeck (on a house). A contractor is telling me the fiberglass deck needs to be replaced, the current fiberglass decking and underlayment removed due to old water damage. We already corrected the water damage caused by leaky railings years ago and there's no leaks. Is the underlayment still ok?