Thanks snoops, and for the info about Nutrak.
When I first read that some sealants were water soluble it did make me wonder how they would work in wet conditions but presumably the plug itself, when it forms and dries, is not water soluble.
I have only just started with the Silca so no significant mess as yet, what little there was seemed to roll up and come off OK. Getting it on clothes would be a different matter I guess.
When I added the Silca at first, it seemed to take a bit longer than I had hoped to seal an existing hole (I used a previously tubed tyre) but fingers crossed. It is quite clumpy in the bottle, I am still not sure if I have mixed it as thoroughly as I’d like. No way would it go through a valve, even with the stem out. Got it in and tyre reseated without fuss though, using an Airshot.
Let’s see how it goes...