Anything that goes over an existing system can be considered a patch. Any patch is subject to the movement of the original substrate, that said I would be very Leary of installing a harder, denser or more rigid product over a softer or more porous one. I would also steer away from the "Cool Coats" of the roofing industry they don't handle ANY pounding and to me seem pork's enough to aid mold growth.
This is just my humble observation and yours may differ and that's OK.
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2020 Precept 34G,
600w 24v solar, Victron 100/50 -BMV712 LiBim 225 BB 200ah. Stehl Dolly, Safe - T- Plus. More to install
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