Having not seen the craft and the extent of the damage I can only guess that
25 years ago someone thought the way to save it for a while longer was to
encapuslate it in ferrocement.

Today people are taking older craft and coating them in epoxy.

This might increase the longiviety for some period but the initial problem
has only been covered up to resurface later under a new owner.

UNLESS YOU CUT IT OUT AND BURN IT ROT SPORES WILL CONTINUE TO EXIST IN THE
WOOD ONLY TO BEGIN THEIR CYCLE OF DESTRUCTION AT THE FIRST
OPPORTUNITY.!!!!!!!!!! ANY CRACK IN THE COATING IS A MEANS FOR MOISTURE
AND AND A WOODEN BOAT MOVES MAKING CRACKS AND THE COATING ONLY
PREVENTS THE MOISTURE FROM EXCAPING. GET THE POINT.

Terry.