Durabond is the best 'build and fill' joint sealer in my opinion. It sets like concrete and isn't easy to sand, but leaves enough room for a top coat or two and you get the best of both worlds. Great for taping corner seams (the wider the better), including adding 90 degree corners over an old fillet when you want a more modern look and don't want to take the old stuff off. If you fill the new cornice so that there is no gap between old and new, it will never fail.