Great video. Love the fiberglass ribs on that boat - looks hell for stout. The owner does nice work.
Concrete is not a great ballast material. Especially if bilges are allowed to be wet. There are additives that can be added to concrete that help a lot, and my ballast looks healthy. I have three tranches of ballast - front (800 kgs removed), aft (guess around 400 kgs) and center/engine room of around 1200-1500 kgs (guess). The only one I am touching is the forward one, and only so I can do some other work. Lead is about 5x more dense than concrete so can free up some space and get the weight lower, though since my boat is a full keel displacement hull, the bilge is pretty deep so may need a false bottom as in the video. Getting that much lead encased in resin without excessive heating will take several pours. For the other areas, have covered with a half inch of floor leveling compound to make it smooth and let it run down sides where there are some small spaces between the hull and ballast. I may glass over it and wrap into the stringers, but not sure. My boat has a pretty dry hull so I'm not too worried.
Hopefully OP will respond. Curious to know more about his situation. Seems odd, but sometimes yards do odd things. They are often decent at general construction but don't have a strong sense of the quirks of a boat.
1970 Willard 36 Sedan Trawler
Current Location: Ensenada MX