My proposed solution to the problem of glossy epoxy is the dust the wet surface of freshly applied epoxy w/ chinchilla bathing dust -which is flour fine grey volcanic dust.
Another possible solution (at least on easily accessible portions of your finished "rock" would be super fine wet/ dry sand paper -maybe 400 grit or finer. Which would de-gloss the shiny surface, but is prolly not so practical over large areas/ craggy areas that area difficult to access.
P.S. The best looking results I've gotten with coloring foam rocks has been using acrylic paints, but I'm not that convinced that such a thin coating of mere paint would hold up well enough (blue and/or pink spots would really displease me when I managed to ding my rock work? The tempts I've done with cement and grout and resulted in the applied materials smoothing out the features of the foam more than I'd like and the super thin layers crack and abrade super easily.
To be forthright, I have not yet played with epoxy coating my foam "rocks" but these are the best laid plans of the mice and man at my house.
Another possible solution (at least on easily accessible portions of your finished "rock" would be super fine wet/ dry sand paper -maybe 400 grit or finer. Which would de-gloss the shiny surface, but is prolly not so practical over large areas/ craggy areas that area difficult to access.
P.S. The best looking results I've gotten with coloring foam rocks has been using acrylic paints, but I'm not that convinced that such a thin coating of mere paint would hold up well enough (blue and/or pink spots would really displease me when I managed to ding my rock work? The tempts I've done with cement and grout and resulted in the applied materials smoothing out the features of the foam more than I'd like and the super thin layers crack and abrade super easily.
To be forthright, I have not yet played with epoxy coating my foam "rocks" but these are the best laid plans of the mice and man at my house.