NE -

My guess is that it's not the sealant, but another factor.

1) Did you check the expiration date on the tube when you used it before?

2) Did you prep the surface by cleaning it first with acetone or something similar?

3) Did you follow manufacturer's instructions for how long you left it clamped in place before removing support?

4) Was the area super dry when you did the work?

NE,

We put wall brackets to hold the undermount sink.

Vee recommended the sealant they use to hold airplane windshields for wet areas.

This is why I always install brackets or wooden side cabinets mountings to hold the sink in place. With a Client, Bill Mumy from the old Lost In Space show, his wife was going to have $5,000 counter tops and splashes in the new kitchen I designed for them. This is 20 years ago when $5K was a lot of money just for the counted tops.

Because the wife and son where real chef's, knew in time the would crack the metal covered porcelain sink. So on the under side of the counter I drilled holes and inserted Brass threaded bushings. With brackets I glued/caulked the sink in place. Then on the sides of the sink cabinet I installed wooden brackets to hold the sink in place.

Then 10 years later they cracked the sink. The counter guy said he would have to fabricate a new top and splash, around $12,000.

The wife called me and I said I can replace the sink, saving the old counter top. I came, let myself in, turned the alarm off and removed the side wooden supports. Cut the caulking/glue using my osculating tool with a scraper blade and removed the supporting brackets. Why my hyrollic jack I lowed he sink. I had to remove the cabinet door stop between the two cabinet doors. Removed the old sink and installed a new one.

Everyone came home and they were amazed on how I got the old sink out and put the new one in. I had to remind the wife she paid me an extra $100 ten years go so I could remove and replace the since without damaging the counter top of slash.