This 1973 Washburn 12 string had a few bridge and saddle issues. All the parts were loose fitting and started tilting, then the saddle cracked and collapsed. The bridge was also lifting quite a bit. I could slide paper under it right up to the pins, and also around the edges. That's a lot of glue failure, so this bridge would have to be removed and re-glued.
The first thing to do is to apply heat to weaken the glue bond. I use a heating blanket that covers the bridge, plugged in to a home made timer/temperature controller. I also monitor the temperature with an infrared thermometer:
Working the bridge off after heating:
As I suspected, the top was finished under the bridge. I will have to scrape all the glue and finish off both top and bridge.
This shape of pocket knife works great for scraping. This bridge was curved side to side, following the curve of the top. I didn't want to flatten that completely after all these years, so I hand scraped instead of using the flat belt sander. I did make it flat from front to back.
For the top I use the knife, a razor blade, and a chisel held straight up. I lightly scribe a line in the finish tracing the footprint of the bridge, and carefully scrape just short of it. It took almost an hour of careful scraping to get down to a clean surface, for a good glue bond.
I made a special clamp and caul combo for gluing bridges. The top caul is stiff hardwood with two thumbscrews that act as secondary clamps. With this caul I only need to put one clamp through the sound hole. This inside caul is notched to clear the braces of the Washburn, and slightly curved to match this bridge.
The trial fit. The pins align the bridge, and masking tape marks the edges. This way I can still see the line when the glue starts to squeeze out.
I prefer to use hide glue for gluing bridges. I'll leave it clamped for a day then wait two more days before putting the strings on.
Clean up the bridge pin holes and it's ready for a new bone saddle and strings: