Thanks. The thing is... there's no way to run such a test. There's an inside to the cabinet under the sink so you can't see whether water is getting behind the sink/cabinet. I guess it's possible that there is a hidden caulking below where I can see it.

If there was a way to -know- I'd love to do nothing.

Thanks again,

---JC

Quote Originally Posted by Mastercarpentry View Post
When I install this kind of backsplash, I lay a healthy bead of silicone under the backsplash to seal it, making sure that none extrudes to where you'd see it in front for appearances sake, and all the professional countertop guys here do exactly the same thing (save for one who epoxies this joint!). So while it may appear that it isn't sealed it very well could be. You can test it by having someone splash water against it while someone is underneath in the cabinets with a light (and a towel just in case) looking for leaks. No leaks = no need for further caulking. If you caulk one done like this anyway, you'll create a dead-air space which if any moisture gets in, will likely grow moldy and odorous so don't just caulk, test it first- then caulk only if it's needed.

(and use silicone)
Phil