Is it necessary to apply a thin coat of finsh over marbleized finish after it sets, or is the marbleized finsh good to go on its own?

It's fine as is.

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It is fine as it is, AS LONG as you're not using metallic, sometimes (not always!) if the finish is thin the metallic can stay on the surface of the finish, or have an edge sticking out of the finish topcoat. You CANNOT feel this with your hands, but it will allow faster degradation of your finish in the marbling area over time with the outdoor elements help. I suggest adding a clear coat over all metallic marbling, one more thin coat is worth the protection it provides.

DR

It should be fine like it is.

Usually, If I'm happy with it, I leave it alone although I usually marble before I put trim wraps on the ends of the marbled area so when I apply finish on the wraps, I just do the whole thing.

Mike (Southgate, MI)
If I don't want to, I don't have to and nobody can make me (except my wife) cuz I'm RETIRED!!

I do the same as Mike so it ends up with an overcoat anyway.

You might think about a vary thin coat of Perma Gloss to be on the safe side. One thine coat well not add any noticeable weight.

Good Wraps Bob

I do the same as Bob and add a thin coat of PG. I've also tried an automotive clear coat and spar urethane to see how it looks.

how would you compare the auto coat, urethane, and permagloss? I have seen several folks on here talk about urethane for a top coat. I have a can for brush on things, it is pretty amber in color. Does the amber show in the thin spray on application, compared to PG? Thanks.

I think that many are making this a lot more complicated than it is. When you marble, the ONLY difference is that there is a LITTLE pigment added to the finish!! There is absolutely nothing to protect except a coat of epoxy. If you normally use an additional coat over your finish, do so, if you don't then don't. I can't see any possible advantage/reason to use PG. urethane, etc over it. Do you put a coat of urethane over your guide wraps?? When you marble, the finish has been tinted, it can't rub off or flake off.

Mike (Southgate, MI)
If I don't want to, I don't have to and nobody can make me (except my wife) cuz I'm RETIRED!!