There have been a bunch of very valuable posts on this. I think it all depends on your local conditions and what you’re trying to achieve. Like Bill, I’m in Florida but in Northwest FL rather than Central. Here we have infrequent frosts, and they’re not sever. No snow of course, but humid and hot summers, Irrigation systems run from about April to November, so almost daily drenching. Also, some of the track can be in intense direct sun, other bits in deep humid shade. I’ve used chicken grit for the past few years (as has Bill). I tried using dilute PVA and it has worked, but as others say it does eventually degrade and wash away. I’ve been using concrete bonding adhesive, both diluted and neat. This does seem to stand the test of time. I lay track mostly on concrete blocks and in most cases the track is not screwed down. I may put in an occasional screw (into a rawlplug or wall anchor set into the block) more to avoid the the track being shifted by a rampant Collie than anything else. I tried an experiment with a block and bit track that was glued to the concrete and ballasted using the bonding adhesive. That test block has been outside for about three years now and has held up well.
Other areas have had different levels of success, but in general it’s doing very well.
Incidentally I don’t have too many issues with grit getting in the points/switches/turnouts. Yes, from time to time, but no worse than bits of twig and other garden detritu.
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