If you are using prusa slicer, ( I am using Orca based on prusa ) there is a setting called "Fuzzy Skin" on the "others" tab that causes the toolhead to "jitter" on the outside wall it is adjustable by a few settings that make it finer or coarser. It almost eliminates layer lines, especially when layer heights are smaller.
In this picture I was not trying to eliminate the layer lines ( I have it set to a fine fuzzy skin ) I was just trying to make it look like the finish of the textured plate it was printed on. It worked very well. The large diameter is 1 3/8" the o ring groove is for a 1" o ring ( for size comparison )
I am not sure how that would affect applying a surface coat or if it would make it harder to pull from the sand. But I think it would be worth a try to print a test piece with the default settings of Fuzzy Skin ( kind of coarse ) and see if it helps you any.
Food for thought
Scott
In this picture I was not trying to eliminate the layer lines ( I have it set to a fine fuzzy skin ) I was just trying to make it look like the finish of the textured plate it was printed on. It worked very well. The large diameter is 1 3/8" the o ring groove is for a 1" o ring ( for size comparison )
I am not sure how that would affect applying a surface coat or if it would make it harder to pull from the sand. But I think it would be worth a try to print a test piece with the default settings of Fuzzy Skin ( kind of coarse ) and see if it helps you any.
Food for thought
Scott