One last question. How about cutting the board out to the nearest joist so that the plaster cove remains supported and then re-board it to there? I get the stop bead but might look naff given the cove probably isn’t perfectly straight and a stop bead would only expose this.
I can understand why the lads don't want to get involved due to the hassle.
Its true that m8y boy who did survey can't say for sure if bond is good or not and tbf, guild of master craftsmen is a load of bollox, just like the amount of rough arse fensa registered window fitters.
So unless, the new skim just drops off, and you strip paper off back to the original skim, (no guarantee that'll be sound though), then your only other option is to get your dec to fill and paint, or you go down reboarding route unfortunately as most on here take a lot of pride in their work and don't want the hassle and comeback so that is the only way.
There are a lot of these threads, and a lot of chancer customers,so I wouldn't usually get involved, but I think you're a genuine guy who paid a very fair price and was let down by a couple of chancers. Think you said that the decs original guy he recommended passed the job on, perhaps he was busy, or your DEC is now back pedalling.
Either way, were they told about how much they were getting beforehand?
If so, then they prob were told that its a nice easy number, bit of paper to get off, but a nice little earner, done in half a day etc, to be confronted with welded on paper.
Paper is a PITA, I get the customer to strip, or stripping is on a day rate. It can be a nightmare.
Anyway, I've got a wedding to attend.
Good luck.